HOWTO - fp2-dev/platform/external/fio - Gitiles

 Table of contents
 -----------------

 1. Overview
 2. How fio works
 3. Running fio
 4. Job file format
 5. Detailed list of parameters
 6. Normal output
 7. Terse output
 8. Trace file format
 9. CPU idleness profiling

 1.0 Overview and history
 ------------------------
 fio was originally written to save me the hassle of writing special test
 case programs when I wanted to test a specific workload, either for
 performance reasons or to find/reproduce a bug. The process of writing
 such a test app can be tiresome, especially if you have to do it often.
 Hence I needed a tool that would be able to simulate a given io workload
 without resorting to writing a tailored test case again and again.

 A test work load is difficult to define, though. There can be any number
 of processes or threads involved, and they can each be using their own
 way of generating io. You could have someone dirtying large amounts of
 memory in an memory mapped file, or maybe several threads issuing
 reads using asynchronous io. fio needed to be flexible enough to
 simulate both of these cases, and many more.

 2.0 How fio works
 -----------------
 The first step in getting fio to simulate a desired io workload, is
 writing a job file describing that specific setup. A job file may contain
 any number of threads and/or files - the typical contents of the job file
 is a global section defining shared parameters, and one or more job
 sections describing the jobs involved. When run, fio parses this file
 and sets everything up as described. If we break down a job from top to
 bottom, it contains the following basic parameters:

 	IO type		Defines the io pattern issued to the file(s).
 			We may only be reading sequentially from this
 			file(s), or we may be writing randomly. Or even
 			mixing reads and writes, sequentially or randomly.

 	Block size	In how large chunks are we issuing io? This may be
 			a single value, or it may describe a range of
 			block sizes.

 	IO size		How much data are we going to be reading/writing.

 	IO engine	How do we issue io? We could be memory mapping the
 			file, we could be using regular read/write, we
 			could be using splice, async io, syslet, or even
 			SG (SCSI generic sg).

 	IO depth	If the io engine is async, how large a queuing
 			depth do we want to maintain?

 	IO type		Should we be doing buffered io, or direct/raw io?

 	Num files	How many files are we spreading the workload over.

 	Num threads	How many threads or processes should we spread
 			this workload over.

 The above are the basic parameters defined for a workload, in addition
 there's a multitude of parameters that modify other aspects of how this
 job behaves.


 3.0 Running fio
 ---------------
 See the README file for command line parameters, there are only a few
 of them.

 Running fio is normally the easiest part - you just give it the job file
 (or job files) as parameters:

 $ fio job_file

 and it will start doing what the job_file tells it to do. You can give
 more than one job file on the command line, fio will serialize the running
 of those files. Internally that is the same as using the 'stonewall'
 parameter described in the parameter section.

 If the job file contains only one job, you may as well just give the
 parameters on the command line. The command line parameters are identical
 to the job parameters, with a few extra that control global parameters
 (see README). For example, for the job file parameter iodepth=2, the
 mirror command line option would be --iodepth 2 or --iodepth=2. You can
 also use the command line for giving more than one job entry. For each
 --name option that fio sees, it will start a new job with that name.
 Command line entries following a --name entry will apply to that job,
 until there are no more entries or a new --name entry is seen. This is
 similar to the job file options, where each option applies to the current
 job until a new [] job entry is seen.

 fio does not need to run as root, except if the files or devices specified
 in the job section requires that. Some other options may also be restricted,
 such as memory locking, io scheduler switching, and decreasing the nice value.


 4.0 Job file format
 -------------------
 As previously described, fio accepts one or more job files describing
 what it is supposed to do. The job file format is the classic ini file,
 where the names enclosed in [] brackets define the job name. You are free
 to use any ascii name you want, except 'global' which has special meaning.
 A global section sets defaults for the jobs described in that file. A job
 may override a global section parameter, and a job file may even have
 several global sections if so desired. A job is only affected by a global
 section residing above it. If the first character in a line is a ';' or a
 '#', the entire line is discarded as a comment.

 So let's look at a really simple job file that defines two processes, each
 randomly reading from a 128MB file.

 ; -- start job file --
 [global]
 rw=randread
 size=128m

 [job1]

 [job2]

 ; -- end job file --

 As you can see, the job file sections themselves are empty as all the
 described parameters are shared. As no filename= option is given, fio
 makes up a filename for each of the jobs as it sees fit. On the command
 line, this job would look as follows:

 $ fio --name=global --rw=randread --size=128m --name=job1 --name=job2


 Let's look at an example that has a number of processes writing randomly
 to files.

 ; -- start job file --
 [random-writers]
 ioengine=libaio
 iodepth=4
 rw=randwrite
 bs=32k
 direct=0
 size=64m
 numjobs=4

 ; -- end job file --

 Here we have no global section, as we only have one job defined anyway.
 We want to use async io here, with a depth of 4 for each file. We also
 increased the buffer size used to 32KB and define numjobs to 4 to
 fork 4 identical jobs. The result is 4 processes each randomly writing
 to their own 64MB file. Instead of using the above job file, you could
 have given the parameters on the command line. For this case, you would
 specify:

 $ fio --name=random-writers --ioengine=libaio --iodepth=4 --rw=randwrite --bs=32k --direct=0 --size=64m --numjobs=4

 When fio is utilized as a basis of any reasonably large test suite, it might be
 desirable to share a set of standardized settings across multiple job files.
 Instead of copy/pasting such settings, any section may pull in an external
 .fio file with 'include filename' directive, as in the following example:

 ; -- start job file including.fio --
 [global]
 filename=/tmp/test
 filesize=1m
 include glob-include.fio

 [test]
 rw=randread
 bs=4k
 time_based=1
 runtime=10
 include test-include.fio
 ; -- end job file including.fio --

 ; -- start job file glob-include.fio --
 thread=1
 group_reporting=1
 ; -- end job file glob-include.fio --

 ; -- start job file test-include.fio --
 ioengine=libaio
 iodepth=4
 ; -- end job file test-include.fio --

 Settings pulled into a section apply to that section only (except global
 section). Include directives may be nested in that any included file may
 contain further include directive(s). Include files may not contain []
 sections.


 4.1 Environment variables
 -------------------------

 fio also supports environment variable expansion in job files. Any
 substring of the form "${VARNAME}" as part of an option value (in other
 words, on the right of the `='), will be expanded to the value of the
 environment variable called VARNAME.  If no such environment variable
 is defined, or VARNAME is the empty string, the empty string will be
 substituted.

 As an example, let's look at a sample fio invocation and job file:

 $ SIZE=64m NUMJOBS=4 fio jobfile.fio

 ; -- start job file --
 [random-writers]
 rw=randwrite
 size=${SIZE}
 numjobs=${NUMJOBS}
 ; -- end job file --

 This will expand to the following equivalent job file at runtime:

 ; -- start job file --
 [random-writers]
 rw=randwrite
 size=64m
 numjobs=4
 ; -- end job file --

 fio ships with a few example job files, you can also look there for
 inspiration.

 4.2 Reserved keywords
 ---------------------

 Additionally, fio has a set of reserved keywords that will be replaced
 internally with the appropriate value. Those keywords are:

 $pagesize	The architecture page size of the running system
 $mb_memory	Megabytes of total memory in the system
 $ncpus		Number of online available CPUs

 These can be used on the command line or in the job file, and will be
 automatically substituted with the current system values when the job
 is run. Simple math is also supported on these keywords, so you can
 perform actions like:

 size=8*$mb_memory

 and get that properly expanded to 8 times the size of memory in the
 machine.


 5.0 Detailed list of parameters
 -------------------------------

 This section describes in details each parameter associated with a job.
 Some parameters take an option of a given type, such as an integer or
 a string. Anywhere a numeric value is required, an arithmetic expression
 may be used, provided it is surrounded by parentheses. Supported operators
 are:

 	addition (+)
 	subtraction (-)
 	multiplication (*)
 	division (/)
 	modulus (%)
 	exponentiation (^)

 For time values in expressions, units are microseconds by default. This is
 different than for time values not in expressions (not enclosed in
 parentheses). The following types are used:

 str	String. This is a sequence of alpha characters.
 time	Integer with possible time suffix. In seconds unless otherwise
 	specified, use eg 10m for 10 minutes. Accepts s/m/h for seconds,
 	minutes, and hours, and accepts 'ms' (or 'msec') for milliseconds,
 	and 'us' (or 'usec') for microseconds.
 int	SI integer. A whole number value, which may contain a suffix
 	describing the base of the number. Accepted suffixes are k/m/g/t/p,
 	meaning kilo, mega, giga, tera, and peta. The suffix is not case
 	sensitive, and you may also include trailing 'b' (eg 'kb' is the same
 	as 'k'). So if you want to specify 4096, you could either write
 	out '4096' or just give 4k. The suffixes signify base 2 values, so
 	1024 is 1k and 1024k is 1m and so on, unless the suffix is explicitly
 	set to a base 10 value using 'kib', 'mib', 'gib', etc. If that is the
 	case, then 1000 is used as the multiplier. This can be handy for
 	disks, since manufacturers generally use base 10 values when listing
 	the capacity of a drive. If the option accepts an upper and lower
 	range, use a colon ':' or minus '-' to separate such values.  May also
 	include a prefix to indicate numbers base. If 0x is used, the number
 	is assumed to be hexadecimal.  See irange.
 bool	Boolean. Usually parsed as an integer, however only defined for
 	true and false (1 and 0).
 irange	Integer range with suffix. Allows value range to be given, such
 	as 1024-4096. A colon may also be used as the separator, eg
 	1k:4k. If the option allows two sets of ranges, they can be
 	specified with a ',' or '/' delimiter: 1k-4k/8k-32k. Also see
 	int.
 float_list	A list of floating numbers, separated by a ':' character.

 With the above in mind, here follows the complete list of fio job
 parameters.

 name=str	ASCII name of the job. This may be used to override the
 		name printed by fio for this job. Otherwise the job
 		name is used. On the command line this parameter has the
 		special purpose of also signaling the start of a new
 		job.

 description=str	Text description of the job. Doesn't do anything except
 		dump this text description when this job is run. It's
 		not parsed.

 directory=str	Prefix filenames with this directory. Used to place files
 		in a different location than "./". See the 'filename' option
 		for escaping certain characters.

 filename=str	Fio normally makes up a filename based on the job name,
 		thread number, and file number. If you want to share
 		files between threads in a job or several jobs, specify
 		a filename for each of them to override the default. If
 		the ioengine used is 'net', the filename is the host, port,
 		and protocol to use in the format of =host,port,protocol.
 		See ioengine=net for more. If the ioengine is file based, you
 		can specify a number of files by separating the names with a
 		':' colon. So if you wanted a job to open /dev/sda and /dev/sdb
 		as the two working files, you would use
 		filename=/dev/sda:/dev/sdb. On Windows, disk devices are
 		accessed as \\.\PhysicalDrive0 for the first device,
 		\\.\PhysicalDrive1 for the second etc. Note: Windows and
 		FreeBSD prevent write access to areas of the disk containing
 		in-use data (e.g. filesystems).
 		If the wanted filename does need to include a colon, then
 		escape that with a '\' character. For instance, if the filename
 		is "/dev/dsk/foo@3,0:c", then you would use
 		filename="/dev/dsk/foo@3,0\:c". '-' is a reserved name, meaning
 		stdin or stdout. Which of the two depends on the read/write
 		direction set.

 filename_format=str
 		If sharing multiple files between jobs, it is usually necessary
 		to  have fio generate the exact names that you want. By default,
 		fio will name a file based on the default file format
 		specification of jobname.jobnumber.filenumber. With this
 		option, that can be customized. Fio will recognize and replace
 		the following keywords in this string:

 		$jobname
 			The name of the worker thread or process.

 		$jobnum
 			The incremental number of the worker thread or
 			process.

 		$filenum
 			The incremental number of the file for that worker
 			thread or process.

 		To have dependent jobs share a set of files, this option can
 		be set to have fio generate filenames that are shared between
 		the two. For instance, if testfiles.$filenum is specified,
 		file number 4 for any job will be named testfiles.4. The
 		default of $jobname.$jobnum.$filenum will be used if
 		no other format specifier is given.

 opendir=str	Tell fio to recursively add any file it can find in this
 		directory and down the file system tree.

 lockfile=str	Fio defaults to not locking any files before it does
 		IO to them. If a file or file descriptor is shared, fio
 		can serialize IO to that file to make the end result
 		consistent. This is usual for emulating real workloads that
 		share files. The lock modes are:

 			none		No locking. The default.
 			exclusive	Only one thread/process may do IO,
 					excluding all others.
 			readwrite	Read-write locking on the file. Many
 					readers may access the file at the
 					same time, but writes get exclusive
 					access.

 readwrite=str
 rw=str		Type of io pattern. Accepted values are:

 			read		Sequential reads
 			write		Sequential writes
 			randwrite	Random writes
 			randread	Random reads
 			rw,readwrite	Sequential mixed reads and writes
 			randrw		Random mixed reads and writes

 		For the mixed io types, the default is to split them 50/50.
 		For certain types of io the result may still be skewed a bit,
 		since the speed may be different. It is possible to specify
 		a number of IO's to do before getting a new offset, this is
 		done by appending a ':<nr>' to the end of the string given.
 		For a random read, it would look like 'rw=randread:8' for
 		passing in an offset modifier with a value of 8. If the
 		suffix is used with a sequential IO pattern, then the value
 		specified will be added to the generated offset for each IO.
 		For instance, using rw=write:4k will skip 4k for every
 		write. It turns sequential IO into sequential IO with holes.
 		See the 'rw_sequencer' option.

 rw_sequencer=str If an offset modifier is given by appending a number to
 		the rw=<str> line, then this option controls how that
 		number modifies the IO offset being generated. Accepted
 		values are:

 			sequential	Generate sequential offset
 			identical	Generate the same offset

 		'sequential' is only useful for random IO, where fio would
 		normally generate a new random offset for every IO. If you
 		append eg 8 to randread, you would get a new random offset for
 		every 8 IO's. The result would be a seek for only every 8
 		IO's, instead of for every IO. Use rw=randread:8 to specify
 		that. As sequential IO is already sequential, setting
 		'sequential' for that would not result in any differences.
 		'identical' behaves in a similar fashion, except it sends
 		the same offset 8 number of times before generating a new
 		offset.

 kb_base=int	The base unit for a kilobyte. The defacto base is 2^10, 1024.
 		Storage manufacturers like to use 10^3 or 1000 as a base
 		ten unit instead, for obvious reasons. Allow values are
 		1024 or 1000, with 1024 being the default.

 unified_rw_reporting=bool	Fio normally reports statistics on a per
 		data direction basis, meaning that read, write, and trim are
 		accounted and reported separately. If this option is set,
 		the fio will sum the results and report them as "mixed"
 		instead.

 randrepeat=bool	For random IO workloads, seed the generator in a predictable
 		way so that results are repeatable across repetitions.

 randseed=int	Seed the random number generators based on this seed value, to
 		be able to control what sequence of output is being generated.
 		If not set, the random sequence depends on the randrepeat
 		setting.

 use_os_rand=bool Fio can either use the random generator supplied by the OS
 		to generator random offsets, or it can use it's own internal
 		generator (based on Tausworthe). Default is to use the
 		internal generator, which is often of better quality and
 		faster.

 fallocate=str	Whether pre-allocation is performed when laying down files.
 		Accepted values are:

 			none		Do not pre-allocate space
 			posix		Pre-allocate via posix_fallocate()
 			keep		Pre-allocate via fallocate() with
 					FALLOC_FL_KEEP_SIZE set
 			0		Backward-compatible alias for 'none'
 			1		Backward-compatible alias for 'posix'

 		May not be available on all supported platforms. 'keep' is only
 		available on Linux.If using ZFS on Solaris this must be set to
 		'none' because ZFS doesn't support it. Default: 'posix'.

 fadvise_hint=bool By default, fio will use fadvise() to advise the kernel
 		on what IO patterns it is likely to issue. Sometimes you
 		want to test specific IO patterns without telling the
 		kernel about it, in which case you can disable this option.
 		If set, fio will use POSIX_FADV_SEQUENTIAL for sequential
 		IO and POSIX_FADV_RANDOM for random IO.

 size=int	The total size of file io for this job. Fio will run until
 		this many bytes has been transferred, unless runtime is
 		limited by other options (such as 'runtime', for instance).
 		Unless specific nrfiles and filesize options are given,
 		fio will divide this size between the available files
 		specified by the job. If not set, fio will use the full
 		size of the given files or devices. If the files do not
 		exist, size must be given. It is also possible to give
 		size as a percentage between 1 and 100. If size=20% is
 		given, fio will use 20% of the full size of the given
 		files or devices.

 io_limit=int	Normally fio operates within the region set by 'size', which
 		means that the 'size' option sets both the region and size of
 		IO to be performed. Sometimes that is not what you want. With
 		this option, it is possible to define just the amount of IO
 		that fio should do. For instance, if 'size' is set to 20G and
 		'io_limit' is set to 5G, fio will perform IO within the first
 		20G but exit when 5G have been done.

 filesize=int	Individual file sizes. May be a range, in which case fio
 		will select sizes for files at random within the given range
 		and limited to 'size' in total (if that is given). If not
 		given, each created file is the same size.

 file_append=bool	Perform IO after the end of the file. Normally fio will
 		operate within the size of a file. If this option is set, then
 		fio will append to the file instead. This has identical
 		behavior to setting offset to the size of a file. This option
 		is ignored on non-regular files.

 fill_device=bool
 fill_fs=bool	Sets size to something really large and waits for ENOSPC (no
 		space left on device) as the terminating condition. Only makes
 		sense with sequential write. For a read workload, the mount
 		point will be filled first then IO started on the result. This
 		option doesn't make sense if operating on a raw device node,
 		since the size of that is already known by the file system.
 		Additionally, writing beyond end-of-device will not return
 		ENOSPC there.

 blocksize=int
 bs=int		The block size used for the io units. Defaults to 4k. Values
 		can be given for both read and writes. If a single int is
 		given, it will apply to both. If a second int is specified
 		after a comma, it will apply to writes only. In other words,
 		the format is either bs=read_and_write or bs=read,write,trim.
 		bs=4k,8k will thus use 4k blocks for reads, 8k blocks for
 		writes, and 8k for trims. You can terminate the list with
 		a trailing comma. bs=4k,8k, would use the default value for
 		trims.. If you only wish to set the write size, you
 		can do so by passing an empty read size - bs=,8k will set
 		8k for writes and leave the read default value.

 blockalign=int
 ba=int		At what boundary to align random IO offsets. Defaults to
 		the same as 'blocksize' the minimum blocksize given.
 		Minimum alignment is typically 512b for using direct IO,
 		though it usually depends on the hardware block size. This
 		option is mutually exclusive with using a random map for
 		files, so it will turn off that option.

 blocksize_range=irange
 bsrange=irange	Instead of giving a single block size, specify a range
 		and fio will mix the issued io block sizes. The issued
 		io unit will always be a multiple of the minimum value
 		given (also see bs_unaligned). Applies to both reads and
 		writes, however a second range can be given after a comma.
 		See bs=.

 bssplit=str	Sometimes you want even finer grained control of the
 		block sizes issued, not just an even split between them.
 		This option allows you to weight various block sizes,
 		so that you are able to define a specific amount of
 		block sizes issued. The format for this option is:

 			bssplit=blocksize/percentage:blocksize/percentage

 		for as many block sizes as needed. So if you want to define
 		a workload that has 50% 64k blocks, 10% 4k blocks, and
 		40% 32k blocks, you would write:

 			bssplit=4k/10:64k/50:32k/40

 		Ordering does not matter. If the percentage is left blank,
 		fio will fill in the remaining values evenly. So a bssplit
 		option like this one:

 			bssplit=4k/50:1k/:32k/

 		would have 50% 4k ios, and 25% 1k and 32k ios. The percentages
 		always add up to 100, if bssplit is given a range that adds
 		up to more, it will error out.

 		bssplit also supports giving separate splits to reads and
 		writes. The format is identical to what bs= accepts. You
 		have to separate the read and write parts with a comma. So
 		if you want a workload that has 50% 2k reads and 50% 4k reads,
 		while having 90% 4k writes and 10% 8k writes, you would
 		specify:

 		bssplit=2k/50:4k/50,4k/90:8k/10

 blocksize_unaligned
 bs_unaligned	If this option is given, any byte size value within bsrange
 		may be used as a block range. This typically wont work with
 		direct IO, as that normally requires sector alignment.

 bs_is_seq_rand	If this option is set, fio will use the normal read,write
 		blocksize settings as sequential,random instead. Any random
 		read or write will use the WRITE blocksize settings, and any
 		sequential read or write will use the READ blocksize setting.

 zero_buffers	If this option is given, fio will init the IO buffers to
 		all zeroes. The default is to fill them with random data.
 		The resulting IO buffers will not be completely zeroed,
 		unless scramble_buffers is also turned off.

 refill_buffers	If this option is given, fio will refill the IO buffers
 		on every submit. The default is to only fill it at init
 		time and reuse that data. Only makes sense if zero_buffers
 		isn't specified, naturally. If data verification is enabled,
 		refill_buffers is also automatically enabled.

 scramble_buffers=bool	If refill_buffers is too costly and the target is
 		using data deduplication, then setting this option will
 		slightly modify the IO buffer contents to defeat normal
 		de-dupe attempts. This is not enough to defeat more clever
 		block compression attempts, but it will stop naive dedupe of
 		blocks. Default: true.

 buffer_compress_percentage=int	If this is set, then fio will attempt to
 		provide IO buffer content (on WRITEs) that compress to
 		the specified level. Fio does this by providing a mix of
 		random data and zeroes. Note that this is per block size
 		unit, for file/disk wide compression level that matches
 		this setting, you'll also want to set refill_buffers.

 buffer_compress_chunk=int	See buffer_compress_percentage. This
 		setting allows fio to manage how big the ranges of random
 		data and zeroed data is. Without this set, fio will
 		provide buffer_compress_percentage of blocksize random
 		data, followed by the remaining zeroed. With this set
 		to some chunk size smaller than the block size, fio can
 		alternate random and zeroed data throughout the IO
 		buffer.

 buffer_pattern=str	If set, fio will fill the io buffers with this
 		pattern. If not set, the contents of io buffers is defined by
 		the other options related to buffer contents. The setting can
 		be any pattern of bytes, and can be prefixed with 0x for hex
 		values. It may also be a string, where the string must then
 		be wrapped with "".

 dedupe_percentage=int	If set, fio will generate this percentage of
 		identical buffers when writing. These buffers will be
 		naturally dedupable. The contents of the buffers depend on
 		what other buffer compression settings have been set. It's
 		possible to have the individual buffers either fully
 		compressible, or not at all. This option only controls the
 		distribution of unique buffers.

 nrfiles=int	Number of files to use for this job. Defaults to 1.

 openfiles=int	Number of files to keep open at the same time. Defaults to
 		the same as nrfiles, can be set smaller to limit the number
 		simultaneous opens.

 file_service_type=str  Defines how fio decides which file from a job to
 		service next. The following types are defined:

 			random	Just choose a file at random.

 			roundrobin  Round robin over open files. This
 				is the default.

 			sequential  Finish one file before moving on to
 				the next. Multiple files can still be
 				open depending on 'openfiles'.

 		The string can have a number appended, indicating how
 		often to switch to a new file. So if option random:4 is
 		given, fio will switch to a new random file after 4 ios
 		have been issued.

 ioengine=str	Defines how the job issues io to the file. The following
 		types are defined:

 			sync	Basic read(2) or write(2) io. lseek(2) is
 				used to position the io location.

 			psync 	Basic pread(2) or pwrite(2) io.

 			vsync	Basic readv(2) or writev(2) IO.

 			psyncv	Basic preadv(2) or pwritev(2) IO.

 			libaio	Linux native asynchronous io. Note that Linux
 				may only support queued behaviour with
 				non-buffered IO (set direct=1 or buffered=0).
 				This engine defines engine specific options.

 			posixaio glibc posix asynchronous io.

 			solarisaio Solaris native asynchronous io.

 			windowsaio Windows native asynchronous io.

 			mmap	File is memory mapped and data copied
 				to/from using memcpy(3).

 			splice	splice(2) is used to transfer the data and
 				vmsplice(2) to transfer data from user
 				space to the kernel.

 			syslet-rw Use the syslet system calls to make
 				regular read/write async.

 			sg	SCSI generic sg v3 io. May either be
 				synchronous using the SG_IO ioctl, or if
 				the target is an sg character device
 				we use read(2) and write(2) for asynchronous
 				io.

 			null	Doesn't transfer any data, just pretends
 				to. This is mainly used to exercise fio
 				itself and for debugging/testing purposes.

 			net	Transfer over the network to given host:port.
 				Depending on the protocol used, the hostname,
 				port, listen and filename options are used to
 				specify what sort of connection to make, while
 				the protocol option determines which protocol
 				will be used.
 				This engine defines engine specific options.

 			netsplice Like net, but uses splice/vmsplice to
 				map data and send/receive.
 				This engine defines engine specific options.

 			cpuio	Doesn't transfer any data, but burns CPU
 				cycles according to the cpuload= and
 				cpucycle= options. Setting cpuload=85
 				will cause that job to do nothing but burn
 				85% of the CPU. In case of SMP machines,
 				use numjobs=<no_of_cpu> to get desired CPU
 				usage, as the cpuload only loads a single
 				CPU at the desired rate.

 			guasi	The GUASI IO engine is the Generic Userspace
 				Asyncronous Syscall Interface approach
 				to async IO. See

 				http://www.xmailserver.org/guasi-lib.html

 				for more info on GUASI.

 			rdma    The RDMA I/O engine  supports  both  RDMA
 				memory semantics (RDMA_WRITE/RDMA_READ) and
 				channel semantics (Send/Recv) for the
 				InfiniBand, RoCE and iWARP protocols.

 			falloc	IO engine that does regular fallocate to
 				simulate data transfer as fio ioengine.
 				DDIR_READ  does fallocate(,mode = keep_size,)
 				DDIR_WRITE does fallocate(,mode = 0)
 				DDIR_TRIM  does fallocate(,mode = punch_hole)

 			e4defrag IO engine that does regular EXT4_IOC_MOVE_EXT
 				ioctls to simulate defragment activity in
 				request to DDIR_WRITE event

 			rbd	IO engine supporting direct access to Ceph
 				Rados Block Devices (RBD) via librbd without
 				the need to use the kernel rbd driver. This
 				ioengine defines engine specific options.

 			gfapi	Using Glusterfs libgfapi sync interface to
 				direct access to Glusterfs volumes without
 				options.

 			gfapi_async Using Glusterfs libgfapi async interface
 				to direct access to Glusterfs volumes without
 				having to go through FUSE. This ioengine
 				defines engine specific options.

 			libhdfs	Read and write through Hadoop (HDFS).
 				The 'filename' option is used to specify host,
 				port of the hdfs name-node to connect. This
 				engine interprets offsets a little
 				differently. In HDFS, files once created
 				cannot be modified. So random writes are not
 				possible. To imitate this, libhdfs engine
 				expects bunch of small files to be created
 				over HDFS, and engine will randomly pick a
 				file out of those files based on the offset
 				generated by fio backend. (see the example
 				job file to create such files, use rw=write
 				option). Please note, you might want to set
 				necessary environment variables to work with
 				hdfs/libhdfs properly.

 			external Prefix to specify loading an external
 				IO engine object file. Append the engine
 				filename, eg ioengine=external:/tmp/foo.o
 				to load ioengine foo.o in /tmp.

 iodepth=int	This defines how many io units to keep in flight against
 		the file. The default is 1 for each file defined in this
 		job, can be overridden with a larger value for higher
 		concurrency. Note that increasing iodepth beyond 1 will not
 		affect synchronous ioengines (except for small degress when
 		verify_async is in use). Even async engines may impose OS
 		restrictions causing the desired depth not to be achieved.
 		This may happen on Linux when using libaio and not setting
 		direct=1, since buffered IO is not async on that OS. Keep an
 		eye on the IO depth distribution in the fio output to verify
 		that the achieved depth is as expected. Default: 1.

 iodepth_batch_submit=int
 iodepth_batch=int This defines how many pieces of IO to submit at once.
 		It defaults to 1 which means that we submit each IO
 		as soon as it is available, but can be raised to submit
 		bigger batches of IO at the time.

 iodepth_batch_complete=int This defines how many pieces of IO to retrieve
 		at once. It defaults to 1 which means that we'll ask
 		for a minimum of 1 IO in the retrieval process from
 		the kernel. The IO retrieval will go on until we
 		hit the limit set by iodepth_low. If this variable is
 		set to 0, then fio will always check for completed
 		events before queuing more IO. This helps reduce
 		IO latency, at the cost of more retrieval system calls.

 iodepth_low=int	The low water mark indicating when to start filling
 		the queue again. Defaults to the same as iodepth, meaning
 		that fio will attempt to keep the queue full at all times.
 		If iodepth is set to eg 16 and iodepth_low is set to 4, then
 		after fio has filled the queue of 16 requests, it will let
 		the depth drain down to 4 before starting to fill it again.

 direct=bool	If value is true, use non-buffered io. This is usually
 		O_DIRECT. Note that ZFS on Solaris doesn't support direct io.
 		On Windows the synchronous ioengines don't support direct io.

 atomic=bool	If value is true, attempt to use atomic direct IO. Atomic
 		writes are guaranteed to be stable once acknowledged by
 		the operating system. Only Linux supports O_ATOMIC right
 		now.

 buffered=bool	If value is true, use buffered io. This is the opposite
 		of the 'direct' option. Defaults to true.

 offset=int	Start io at the given offset in the file. The data before
 		the given offset will not be touched. This effectively
 		caps the file size at real_size - offset.

 offset_increment=int	If this is provided, then the real offset becomes
 		offset + offset_increment * thread_number, where the thread
 		number is a counter that starts at 0 and is incremented for
 		each sub-job (i.e. when numjobs option is specified). This
 		option is useful if there are several jobs which are intended
 		to operate on a file in parallel disjoint segments, with
 		even spacing between the starting points.

 number_ios=int	Fio will normally perform IOs until it has exhausted the size
 		of the region set by size=, or if it exhaust the allocated
 		time (or hits an error condition). With this setting, the
 		range/size can be set independently of the number of IOs to
 		perform. When fio reaches this number, it will exit normally
 		and report status. Note that this does not extend the amount
 		of IO that will be done, it will only stop fio if this
 		condition is met before other end-of-job criteria.

 fsync=int	If writing to a file, issue a sync of the dirty data
 		for every number of blocks given. For example, if you give
 		32 as a parameter, fio will sync the file for every 32
 		writes issued. If fio is using non-buffered io, we may
 		not sync the file. The exception is the sg io engine, which
 		synchronizes the disk cache anyway.

 fdatasync=int	Like fsync= but uses fdatasync() to only sync data and not
 		metadata blocks.
 		In FreeBSD and Windows there is no fdatasync(), this falls back to
 		using fsync()

 sync_file_range=str:val	Use sync_file_range() for every 'val' number of
 		write operations. Fio will track range of writes that
 		have happened since the last sync_file_range() call. 'str'
 		can currently be one or more of:

 		wait_before	SYNC_FILE_RANGE_WAIT_BEFORE
 		write		SYNC_FILE_RANGE_WRITE
 		wait_after	SYNC_FILE_RANGE_WAIT_AFTER

 		So if you do sync_file_range=wait_before,write:8, fio would
 		use SYNC_FILE_RANGE_WAIT_BEFORE | SYNC_FILE_RANGE_WRITE for
 		every 8 writes. Also see the sync_file_range(2) man page.
 		This option is Linux specific.

 overwrite=bool	If true, writes to a file will always overwrite existing
 		data. If the file doesn't already exist, it will be
 		created before the write phase begins. If the file exists
 		and is large enough for the specified write phase, nothing
 		will be done.

 end_fsync=bool	If true, fsync file contents when a write stage has completed.

 fsync_on_close=bool	If true, fio will fsync() a dirty file on close.
 		This differs from end_fsync in that it will happen on every
 		file close, not just at the end of the job.

 rwmixread=int	How large a percentage of the mix should be reads.

 rwmixwrite=int	How large a percentage of the mix should be writes. If both
 		rwmixread and rwmixwrite is given and the values do not add
 		up to 100%, the latter of the two will be used to override
 		the first. This may interfere with a given rate setting,
 		if fio is asked to limit reads or writes to a certain rate.
 		If that is the case, then the distribution may be skewed.

 random_distribution=str:float	By default, fio will use a completely uniform
 		random distribution when asked to perform random IO. Sometimes
 		it is useful to skew the distribution in specific ways,
 		ensuring that some parts of the data is more hot than others.
 		fio includes the following distribution models:

 		random		Uniform random distribution
 		zipf		Zipf distribution
 		pareto		Pareto distribution

 		When using a zipf or pareto distribution, an input value
 		is also needed to define the access pattern. For zipf, this
 		is the zipf theta. For pareto, it's the pareto power. Fio
 		includes a test program, genzipf, that can be used visualize
 		what the given input values will yield in terms of hit rates.
 		If you wanted to use zipf with a theta of 1.2, you would use
 		random_distribution=zipf:1.2 as the option. If a non-uniform
 		model is used, fio will disable use of the random map.

 percentage_random=int	For a random workload, set how big a percentage should
 		be random. This defaults to 100%, in which case the workload
 		is fully random. It can be set from anywhere from 0 to 100.
 		Setting it to 0 would make the workload fully sequential. Any
 		setting in between will result in a random mix of sequential
 		and random IO, at the given percentages. It is possible to
 		set different values for reads, writes, and trim. To do so,
 		simply use a comma separated list. See blocksize.

 norandommap	Normally fio will cover every block of the file when doing
 		random IO. If this option is given, fio will just get a
 		new random offset without looking at past io history. This
 		means that some blocks may not be read or written, and that
 		some blocks may be read/written more than once. This option
 		is mutually exclusive with verify= if and only if multiple
 		blocksizes (via bsrange=) are used, since fio only tracks
 		complete rewrites of blocks.

 softrandommap=bool See norandommap. If fio runs with the random block map
 		enabled and it fails to allocate the map, if this option is
 		set it will continue without a random block map. As coverage
 		will not be as complete as with random maps, this option is
 		disabled by default.

 random_generator=str	Fio supports the following engines for generating
 		IO offsets for random IO:

 		tausworthe	Strong 2^88 cycle random number generator
 		lfsr		Linear feedback shift register generator

 		Tausworthe is a strong random number generator, but it
 		requires tracking on the side if we want to ensure that
 		blocks are only read or written once. LFSR guarantees
 		that we never generate the same offset twice, and it's
 		also less computationally expensive. It's not a true
 		random generator, however, though for IO purposes it's
 		typically good enough. LFSR only works with single
 		block sizes, not with workloads that use multiple block
 		sizes. If used with such a workload, fio may read or write
 		some blocks multiple times.

 nice=int	Run the job with the given nice value. See man nice(2).

 prio=int	Set the io priority value of this job. Linux limits us to
 		a positive value between 0 and 7, with 0 being the highest.
 		See man ionice(1).

 prioclass=int	Set the io priority class. See man ionice(1).

 thinktime=int	Stall the job x microseconds after an io has completed before
 		issuing the next. May be used to simulate processing being
 		done by an application. See thinktime_blocks and
 		thinktime_spin.

 thinktime_spin=int
 		Only valid if thinktime is set - pretend to spend CPU time
 		doing something with the data received, before falling back
 		to sleeping for the rest of the period specified by
 		thinktime.

 thinktime_blocks=int
 		Only valid if thinktime is set - control how many blocks
 		to issue, before waiting 'thinktime' usecs. If not set,
 		defaults to 1 which will make fio wait 'thinktime' usecs
 		after every block. This effectively makes any queue depth
 		setting redundant, since no more than 1 IO will be queued
 		before we have to complete it and do our thinktime. In
 		other words, this setting effectively caps the queue depth
 		if the latter is larger.

 rate=int	Cap the bandwidth used by this job. The number is in bytes/sec,
 		the normal suffix rules apply. You can use rate=500k to limit
 		reads and writes to 500k each, or you can specify read and
 		writes separately. Using rate=1m,500k would limit reads to
 		1MB/sec and writes to 500KB/sec. Capping only reads or
 		writes can be done with rate=,500k or rate=500k,. The former
 		will only limit writes (to 500KB/sec), the latter will only
 		limit reads.

 ratemin=int	Tell fio to do whatever it can to maintain at least this
 		bandwidth. Failing to meet this requirement, will cause
 		the job to exit. The same format as rate is used for
 		read vs write separation.

 rate_iops=int	Cap the bandwidth to this number of IOPS. Basically the same
 		as rate, just specified independently of bandwidth. If the
 		job is given a block size range instead of a fixed value,
 		the smallest block size is used as the metric. The same format
 		as rate is used for read vs write separation.

 rate_iops_min=int If fio doesn't meet this rate of IO, it will cause
 		the job to exit. The same format as rate is used for read vs
 		write separation.

 latency_target=int	If set, fio will attempt to find the max performance
 		point that the given workload will run at while maintaining a
 		latency below this target. The values is given in microseconds.
 		See latency_window and latency_percentile

 latency_window=int	Used with latency_target to specify the sample window
 		that the job is run at varying queue depths to test the
 		performance. The value is given in microseconds.

 latency_percentile=float	The percentage of IOs that must fall within the
 		criteria specified by latency_target and latency_window. If not
 		set, this defaults to 100.0, meaning that all IOs must be equal
 		or below to the value set by latency_target.

 max_latency=int	If set, fio will exit the job if it exceeds this maximum
 		latency. It will exit with an ETIME error.

 ratecycle=int	Average bandwidth for 'rate' and 'ratemin' over this number
 		of milliseconds.

 cpumask=int	Set the CPU affinity of this job. The parameter given is a
 		bitmask of allowed CPU's the job may run on. So if you want
 		the allowed CPUs to be 1 and 5, you would pass the decimal
 		value of (1 << 1 | 1 << 5), or 34. See man
 		sched_setaffinity(2). This may not work on all supported
 		operating systems or kernel versions. This option doesn't
 		work well for a higher CPU count than what you can store in
 		an integer mask, so it can only control cpus 1-32. For
 		boxes with larger CPU counts, use cpus_allowed.

 cpus_allowed=str Controls the same options as cpumask, but it allows a text
 		setting of the permitted CPUs instead. So to use CPUs 1 and
 		5, you would specify cpus_allowed=1,5. This options also
 		allows a range of CPUs. Say you wanted a binding to CPUs
 		1, 5, and 8-15, you would set cpus_allowed=1,5,8-15.

 cpus_allowed_policy=str Set the policy of how fio distributes the CPUs
 		specified by cpus_allowed or cpumask. Two policies are
 		supported:

 		shared	All jobs will share the CPU set specified.
 		split	Each job will get a unique CPU from the CPU set.

 		'shared' is the default behaviour, if the option isn't
 		specified. If split is specified, then fio will will assign
 		one cpu per job. If not enough CPUs are given for the jobs
 		listed, then fio will roundrobin the CPUs in the set.

 numa_cpu_nodes=str Set this job running on spcified NUMA nodes' CPUs. The
 		arguments allow comma delimited list of cpu numbers,
 		A-B ranges, or 'all'. Note, to enable numa options support,
 		fio must be built on a system with libnuma-dev(el) installed.

 numa_mem_policy=str Set this job's memory policy and corresponding NUMA
 		nodes. Format of the argements:
 			<mode>[:<nodelist>]
 		`mode' is one of the following memory policy:
 			default, prefer, bind, interleave, local
 		For `default' and `local' memory policy, no node is
 		needed to be specified.
 		For `prefer', only one node is allowed.
 		For `bind' and `interleave', it allow comma delimited
 		list of numbers, A-B ranges, or 'all'.

 startdelay=time	Start this job the specified number of seconds after fio
 		has started. Only useful if the job file contains several
 		jobs, and you want to delay starting some jobs to a certain
 		time.

 runtime=time	Tell fio to terminate processing after the specified number
 		of seconds. It can be quite hard to determine for how long
 		a specified job will run, so this parameter is handy to
 		cap the total runtime to a given time.

 time_based	If set, fio will run for the duration of the runtime
 		specified even if the file(s) are completely read or
 		written. It will simply loop over the same workload
 		as many times as the runtime allows.

 ramp_time=time	If set, fio will run the specified workload for this amount
 		of time before logging any performance numbers. Useful for
 		letting performance settle before logging results, thus
 		minimizing the runtime required for stable results. Note
 		that the ramp_time is considered lead in time for a job,
 		thus it will increase the total runtime if a special timeout
 		or runtime is specified.

 invalidate=bool	Invalidate the buffer/page cache parts for this file prior
 		to starting io. Defaults to true.

 sync=bool	Use sync io for buffered writes. For the majority of the
 		io engines, this means using O_SYNC.

 iomem=str
 mem=str		Fio can use various types of memory as the io unit buffer.
 		The allowed values are:

 			malloc	Use memory from malloc(3) as the buffers.

 			shm	Use shared memory as the buffers. Allocated
 				through shmget(2).

 			shmhuge	Same as shm, but use huge pages as backing.

 			mmap	Use mmap to allocate buffers. May either be
 				anonymous memory, or can be file backed if
 				a filename is given after the option. The
 				format is mem=mmap:/path/to/file.

 			mmaphuge Use a memory mapped huge file as the buffer
 				backing. Append filename after mmaphuge, ala
 				mem=mmaphuge:/hugetlbfs/file

 		The area allocated is a function of the maximum allowed
 		bs size for the job, multiplied by the io depth given. Note
 		that for shmhuge and mmaphuge to work, the system must have
 		free huge pages allocated. This can normally be checked
 		and set by reading/writing /proc/sys/vm/nr_hugepages on a
 		Linux system. Fio assumes a huge page is 4MB in size. So
 		to calculate the number of huge pages you need for a given
 		job file, add up the io depth of all jobs (normally one unless
 		iodepth= is used) and multiply by the maximum bs set. Then
 		divide that number by the huge page size. You can see the
 		size of the huge pages in /proc/meminfo. If no huge pages
 		are allocated by having a non-zero number in nr_hugepages,
 		using mmaphuge or shmhuge will fail. Also see hugepage-size.

 		mmaphuge also needs to have hugetlbfs mounted and the file
 		location should point there. So if it's mounted in /huge,
 		you would use mem=mmaphuge:/huge/somefile.

 iomem_align=int	This indiciates the memory alignment of the IO memory buffers.
 		Note that the given alignment is applied to the first IO unit
 		buffer, if using iodepth the alignment of the following buffers
 		are given by the bs used. In other words, if using a bs that is
 		a multiple of the page sized in the system, all buffers will
 		be aligned to this value. If using a bs that is not page
 		aligned, the alignment of subsequent IO memory buffers is the
 		sum of the iomem_align and bs used.

 hugepage-size=int
 		Defines the size of a huge page. Must at least be equal
 		to the system setting, see /proc/meminfo. Defaults to 4MB.
 		Should probably always be a multiple of megabytes, so using
 		hugepage-size=Xm is the preferred way to set this to avoid
 		setting a non-pow-2 bad value.

 exitall		When one job finishes, terminate the rest. The default is
 		to wait for each job to finish, sometimes that is not the
 		desired action.

 bwavgtime=int	Average the calculated bandwidth over the given time. Value
 		is specified in milliseconds.

 iopsavgtime=int	Average the calculated IOPS over the given time. Value
 		is specified in milliseconds.

 create_serialize=bool	If true, serialize the file creating for the jobs.
 			This may be handy to avoid interleaving of data
 			files, which may greatly depend on the filesystem
 			used and even the number of processors in the system.

 create_fsync=bool	fsync the data file after creation. This is the
 			default.

 create_on_open=bool	Don't pre-setup the files for IO, just create open()
 			when it's time to do IO to that file.

 create_only=bool	If true, fio will only run the setup phase of the job.
 			If files need to be laid out or updated on disk, only
 			that will be done. The actual job contents are not
 			executed.

 pre_read=bool	If this is given, files will be pre-read into memory before
 		starting the given IO operation. This will also clear
 		the 'invalidate' flag, since it is pointless to pre-read
 		and then drop the cache. This will only work for IO engines
 		that are seekable, since they allow you to read the same data
 		multiple times. Thus it will not work on eg network or splice
 		IO.

 unlink=bool	Unlink the job files when done. Not the default, as repeated
 		runs of that job would then waste time recreating the file
 		set again and again.

 loops=int	Run the specified number of iterations of this job. Used
 		to repeat the same workload a given number of times. Defaults
 		to 1.

 verify_only	Do not perform specified workload---only verify data still
 		matches previous invocation of this workload. This option
 		allows one to check data multiple times at a later date
 		without overwriting it. This option makes sense only for
 		workloads that write data, and does not support workloads
 		with the time_based option set.

 do_verify=bool	Run the verify phase after a write phase. Only makes sense if
 		verify is set. Defaults to 1.

 verify=str	If writing to a file, fio can verify the file contents
 		after each iteration of the job. The allowed values are:

 			md5	Use an md5 sum of the data area and store
 				it in the header of each block.

 			crc64	Use an experimental crc64 sum of the data
 				area and store it in the header of each
 				block.

 			crc32c	Use a crc32c sum of the data area and store
 				it in the header of each block.

 			crc32c-intel Use hardware assisted crc32c calcuation
 				provided on SSE4.2 enabled processors. Falls
 				back to regular software crc32c, if not
 				supported by the system.

 			crc32	Use a crc32 sum of the data area and store
 				it in the header of each block.

 			crc16	Use a crc16 sum of the data area and store
 				it in the header of each block.

 			crc7	Use a crc7 sum of the data area and store
 				it in the header of each block.

 			xxhash	Use xxhash as the checksum function. Generally
 				the fastest software checksum that fio
 				supports.

 			sha512	Use sha512 as the checksum function.

 			sha256	Use sha256 as the checksum function.

 			sha1	Use optimized sha1 as the checksum function.

 			meta	Write extra information about each io
 				(timestamp, block number etc.). The block
 				number is verified. The io sequence number is
 				verified for workloads that write data.
 				See also verify_pattern.

 			null	Only pretend to verify. Useful for testing
 				internals with ioengine=null, not for much
 				else.

 		This option can be used for repeated burn-in tests of a
 		system to make sure that the written data is also
 		correctly read back. If the data direction given is
 		a read or random read, fio will assume that it should
 		verify a previously written file. If the data direction
 		includes any form of write, the verify will be of the
 		newly written data.

 verifysort=bool	If set, fio will sort written verify blocks when it deems
 		it faster to read them back in a sorted manner. This is
 		often the case when overwriting an existing file, since
 		the blocks are already laid out in the file system. You
 		can ignore this option unless doing huge amounts of really
 		fast IO where the red-black tree sorting CPU time becomes
 		significant.

 verify_offset=int	Swap the verification header with data somewhere else
 			in the block before writing. Its swapped back before
 			verifying.

 verify_interval=int	Write the verification header at a finer granularity
 			than the blocksize. It will be written for chunks the
 			size of header_interval. blocksize should divide this
 			evenly.

 verify_pattern=str	If set, fio will fill the io buffers with this
 		pattern. Fio defaults to filling with totally random
 		bytes, but sometimes it's interesting to fill with a known
 		pattern for io verification purposes. Depending on the
 		width of the pattern, fio will fill 1/2/3/4 bytes of the
 		buffer at the time(it can be either a decimal or a hex number).
 		The verify_pattern if larger than a 32-bit quantity has to
 		be a hex number that starts with either "0x" or "0X". Use
 		with verify=meta.

 verify_fatal=bool	Normally fio will keep checking the entire contents
 		before quitting on a block verification failure. If this
 		option is set, fio will exit the job on the first observed
 		failure.

 verify_dump=bool	If set, dump the contents of both the original data
 		block and the data block we read off disk to files. This
 		allows later analysis to inspect just what kind of data
 		corruption occurred. Off by default.

 verify_async=int	Fio will normally verify IO inline from the submitting
 		thread. This option takes an integer describing how many
 		async offload threads to create for IO verification instead,
 		causing fio to offload the duty of verifying IO contents
 		to one or more separate threads. If using this offload
 		option, even sync IO engines can benefit from using an
 		iodepth setting higher than 1, as it allows them to have
 		IO in flight while verifies are running.

 verify_async_cpus=str	Tell fio to set the given CPU affinity on the
 		async IO verification threads. See cpus_allowed for the
 		format used.

 verify_backlog=int	Fio will normally verify the written contents of a
 		job that utilizes verify once that job has completed. In
 		other words, everything is written then everything is read
 		back and verified. You may want to verify continually
 		instead for a variety of reasons. Fio stores the meta data
 		associated with an IO block in memory, so for large
 		verify workloads, quite a bit of memory would be used up
 		holding this meta data. If this option is enabled, fio
 		will write only N blocks before verifying these blocks.

 verify_backlog_batch=int	Control how many blocks fio will verify
 		if verify_backlog is set. If not set, will default to
 		the value of verify_backlog (meaning the entire queue
 		is read back and verified).  If verify_backlog_batch is
 		less than verify_backlog then not all blocks will be verified,
 		if verify_backlog_batch is larger than verify_backlog, some
 		blocks will be verified more than once.

 stonewall
 wait_for_previous Wait for preceding jobs in the job file to exit, before
 		starting this one. Can be used to insert serialization
 		points in the job file. A stone wall also implies starting
 		a new reporting group.

 new_group	Start a new reporting group. See: group_reporting.

 numjobs=int	Create the specified number of clones of this job. May be
 		used to setup a larger number of threads/processes doing
 		the same thing. Each thread is reported separately; to see
 		statistics for all clones as a whole, use group_reporting in
 		conjunction with new_group.

 group_reporting	It may sometimes be interesting to display statistics for
 		groups of jobs as a whole instead of for each individual job.
 		This is especially true if 'numjobs' is used; looking at
 		individual thread/process output quickly becomes unwieldy.
 		To see the final report per-group instead of per-job, use
 		'group_reporting'. Jobs in a file will be part of the same
 		reporting group, unless if separated by a stonewall, or by
 		using 'new_group'.

 thread		fio defaults to forking jobs, however if this option is
 		given, fio will use pthread_create(3) to create threads
 		instead.

 zonesize=int	Divide a file into zones of the specified size. See zoneskip.

 zoneskip=int	Skip the specified number of bytes when zonesize data has
 		been read. The two zone options can be used to only do
 		io on zones of a file.

 write_iolog=str	Write the issued io patterns to the specified file. See
 		read_iolog.  Specify a separate file for each job, otherwise
 		the iologs will be interspersed and the file may be corrupt.

 read_iolog=str	Open an iolog with the specified file name and replay the
 		io patterns it contains. This can be used to store a
 		workload and replay it sometime later. The iolog given
 		may also be a blktrace binary file, which allows fio
 		to replay a workload captured by blktrace. See blktrace
 		for how to capture such logging data. For blktrace replay,
 		the file needs to be turned into a blkparse binary data
 		file first (blkparse <device> -o /dev/null -d file_for_fio.bin).

 replay_no_stall=int When replaying I/O with read_iolog the default behavior
 		is to attempt to respect the time stamps within the log and
 		replay them with the appropriate delay between IOPS.  By
 		setting this variable fio will not respect the timestamps and
 		attempt to replay them as fast as possible while still
 		respecting ordering.  The result is the same I/O pattern to a
 		given device, but different timings.

 replay_redirect=str While replaying I/O patterns using read_iolog the
 		default behavior is to replay the IOPS onto the major/minor
 		device that each IOP was recorded from.  This is sometimes
 		undesirable because on a different machine those major/minor
 		numbers can map to a different device.  Changing hardware on
 		the same system can also result in a different major/minor
 		mapping.  Replay_redirect causes all IOPS to be replayed onto
 		the single specified device regardless of the device it was
 		recorded from. i.e. replay_redirect=/dev/sdc would cause all
 		IO in the blktrace to be replayed onto /dev/sdc.  This means
 		multiple devices will be replayed onto a single, if the trace
 		contains multiple devices.  If you want multiple devices to be
 		replayed concurrently to multiple redirected devices you must
 		blkparse your trace into separate traces and replay them with
 		independent fio invocations.  Unfortuantely this also breaks
 		the strict time ordering between multiple device accesses.

 write_bw_log=str If given, write a bandwidth log of the jobs in this job
 		file. Can be used to store data of the bandwidth of the
 		jobs in their lifetime. The included fio_generate_plots
 		script uses gnuplot to turn these text files into nice
 		graphs. See write_lat_log for behaviour of given
 		filename. For this option, the suffix is _bw.x.log, where
 		x is the index of the job (1..N, where N is the number of
 		jobs).

 write_lat_log=str Same as write_bw_log, except that this option stores io
 		submission, completion, and total latencies instead. If no
 		filename is given with this option, the default filename of
 		"jobname_type.log" is used. Even if the filename is given,
 		fio will still append the type of log. So if one specifies

 		write_lat_log=foo

 		The actual log names will be foo_slat.x.log, foo_clat.x.log,
 		and foo_lat.x.log, where x is the index of the job (1..N,
 		where N is the number of jobs). This helps fio_generate_plot
 		fine the logs automatically.

 write_iops_log=str Same as write_bw_log, but writes IOPS. If no filename is
 		given with this option, the default filename of
 		"jobname_type.x.log" is used,where x is the index of the job
 		(1..N, where N is the number of jobs). Even if the filename
 		is given, fio will still append the type of log.

 log_avg_msec=int By default, fio will log an entry in the iops, latency,
 		or bw log for every IO that completes. When writing to the
 		disk log, that can quickly grow to a very large size. Setting
 		this option makes fio average the each log entry over the
 		specified period of time, reducing the resolution of the log.
 		Defaults to 0.

 log_offset=int	If this is set, the iolog options will include the byte
 		offset for the IO entry as well as the other data values.

 log_compression=int	If this is set, fio will compress the IO logs as
 		it goes, to keep the memory footprint lower. When a log
 		reaches the specified size, that chunk is removed and
 		compressed in the background. Given that IO logs are
 		fairly highly compressible, this yields a nice memory
 		savings for longer runs. The downside is that the
 		compression will consume some background CPU cycles, so
 		it may impact the run. This, however, is also true if
 		the logging ends up consuming most of the system memory.
 		So pick your poison. The IO logs are saved normally at the
 		end of a run, by decompressing the chunks and storing them
 		in the specified log file. This feature depends on the
 		availability of zlib.

 log_store_compressed=bool	If set, and log_compression is also set,
 		fio will store the log files in a compressed format. They
 		can be decompressed with fio, using the --inflate-log
 		command line parameter. The files will be stored with a
 		.fz suffix.

 lockmem=int	Pin down the specified amount of memory with mlock(2). Can
 		potentially be used instead of removing memory or booting
 		with less memory to simulate a smaller amount of memory.
 		The amount specified is per worker.

 exec_prerun=str	Before running this job, issue the command specified
 		through system(3). Output is redirected in a file called
 		jobname.prerun.txt.

 exec_postrun=str After the job completes, issue the command specified
 		 though system(3). Output is redirected in a file called
 		 jobname.postrun.txt.

 ioscheduler=str	Attempt to switch the device hosting the file to the specified
 		io scheduler before running.

 disk_util=bool	Generate disk utilization statistics, if the platform
 		supports it. Defaults to on.

 disable_lat=bool Disable measurements of total latency numbers. Useful
 		only for cutting back the number of calls to gettimeofday,
 		as that does impact performance at really high IOPS rates.
 		Note that to really get rid of a large amount of these
 		calls, this option must be used with disable_slat and
 		disable_bw as well.

 disable_clat=bool Disable measurements of completion latency numbers. See
 		disable_lat.

 disable_slat=bool Disable measurements of submission latency numbers. See
 		disable_slat.

 disable_bw=bool	Disable measurements of throughput/bandwidth numbers. See
 		disable_lat.

 clat_percentiles=bool Enable the reporting of percentiles of
 		 completion latencies.

 percentile_list=float_list Overwrite the default list of percentiles
 		for completion latencies. Each number is a floating
 		number in the range (0,100], and the maximum length of
 		the list is 20. Use ':' to separate the numbers, and
 		list the numbers in ascending order. For example,
 		--percentile_list=99.5:99.9 will cause fio to report
 		the values of completion latency below which 99.5% and
 		99.9% of the observed latencies fell, respectively.

 clocksource=str	Use the given clocksource as the base of timing. The
 		supported options are:

 			gettimeofday	gettimeofday(2)

 			clock_gettime	clock_gettime(2)

 			cpu		Internal CPU clock source

 		cpu is the preferred clocksource if it is reliable, as it
 		is very fast (and fio is heavy on time calls). Fio will
 		automatically use this clocksource if it's supported and
 		considered reliable on the system it is running on, unless
 		another clocksource is specifically set. For x86/x86-64 CPUs,
 		this means supporting TSC Invariant.

 gtod_reduce=bool Enable all of the gettimeofday() reducing options
 		(disable_clat, disable_slat, disable_bw) plus reduce
 		precision of the timeout somewhat to really shrink
 		the gettimeofday() call count. With this option enabled,
 		we only do about 0.4% of the gtod() calls we would have
 		done if all time keeping was enabled.

 gtod_cpu=int	Sometimes it's cheaper to dedicate a single thread of
 		execution to just getting the current time. Fio (and
 		databases, for instance) are very intensive on gettimeofday()
 		calls. With this option, you can set one CPU aside for
 		doing nothing but logging current time to a shared memory
 		location. Then the other threads/processes that run IO
 		workloads need only copy that segment, instead of entering
 		the kernel with a gettimeofday() call. The CPU set aside
 		for doing these time calls will be excluded from other
 		uses. Fio will manually clear it from the CPU mask of other
 		jobs.

 continue_on_error=str	Normally fio will exit the job on the first observed
 		failure. If this option is set, fio will continue the job when
 		there is a 'non-fatal error' (EIO or EILSEQ) until the runtime
 		is exceeded or the I/O size specified is completed. If this
 		option is used, there are two more stats that are appended,
 		the total error count and the first error. The error field
 		given in the stats is the first error that was hit during the
 		run.

 		The allowed values are:

 			none	Exit on any IO or verify errors.

 			read	Continue on read errors, exit on all others.

 			write	Continue on write errors, exit on all others.

 			io	Continue on any IO error, exit on all others.

 			verify	Continue on verify errors, exit on all others.

 			all	Continue on all errors.

 			0		Backward-compatible alias for 'none'.

 			1		Backward-compatible alias for 'all'.

 ignore_error=str Sometimes you want to ignore some errors during test
 		 in that case you can specify error list for each error type.
 		 ignore_error=READ_ERR_LIST,WRITE_ERR_LIST,VERIFY_ERR_LIST
 		 errors for given error type is separated with ':'. Error
 		 may be symbol ('ENOSPC', 'ENOMEM') or integer.
 		 Example:
 			ignore_error=EAGAIN,ENOSPC:122
 		 This option will ignore EAGAIN from READ, and ENOSPC and
 		 122(EDQUOT) from WRITE.

 error_dump=bool If set dump every error even if it is non fatal, true
 		by default. If disabled only fatal error will be dumped

 cgroup=str	Add job to this control group. If it doesn't exist, it will
 		be created. The system must have a mounted cgroup blkio
 		mount point for this to work. If your system doesn't have it
 		mounted, you can do so with:

 		# mount -t cgroup -o blkio none /cgroup

 cgroup_weight=int	Set the weight of the cgroup to this value. See
 		the documentation that comes with the kernel, allowed values
 		are in the range of 100..1000.

 cgroup_nodelete=bool Normally fio will delete the cgroups it has created after
 		the job completion. To override this behavior and to leave
 		cgroups around after the job completion, set cgroup_nodelete=1.
 		This can be useful if one wants to inspect various cgroup
 		files after job completion. Default: false

 uid=int		Instead of running as the invoking user, set the user ID to
 		this value before the thread/process does any work.

 gid=int		Set group ID, see uid.

 flow_id=int	The ID of the flow. If not specified, it defaults to being a
 		global flow. See flow.

 flow=int	Weight in token-based flow control. If this value is used, then
 		there is a 'flow counter' which is used to regulate the
 		proportion of activity between two or more jobs. fio attempts
 		to keep this flow counter near zero. The 'flow' parameter
 		stands for how much should be added or subtracted to the flow
 		counter on each iteration of the main I/O loop. That is, if
 		one job has flow=8 and another job has flow=-1, then there
 		will be a roughly 1:8 ratio in how much one runs vs the other.

 flow_watermark=int	The maximum value that the absolute value of the flow
 		counter is allowed to reach before the job must wait for a
 		lower value of the counter.

 flow_sleep=int	The period of time, in microseconds, to wait after the flow
 		watermark has been exceeded before retrying operations

 In addition, there are some parameters which are only valid when a specific
 ioengine is in use. These are used identically to normal parameters, with the
 caveat that when used on the command line, they must come after the ioengine
 that defines them is selected.

 [libaio] userspace_reap Normally, with the libaio engine in use, fio will use
 		the io_getevents system call to reap newly returned events.
 		With this flag turned on, the AIO ring will be read directly
 		from user-space to reap events. The reaping mode is only
 		enabled when polling for a minimum of 0 events (eg when
 		iodepth_batch_complete=0).

 [cpu] cpuload=int Attempt to use the specified percentage of CPU cycles.

 [cpu] cpuchunks=int Split the load into cycles of the given time. In
 		microseconds.

 [cpu] exit_on_io_done=bool Detect when IO threads are done, then exit.

 [netsplice] hostname=str
 [net] hostname=str The host name or IP address to use for TCP or UDP based IO.
 		If the job is a TCP listener or UDP reader, the hostname is not
 		used and must be omitted unless it is a valid UDP multicast
 		address.

 [netsplice] port=int
 [net] port=int	The TCP or UDP port to bind to or connect to. If this is used
 with numjobs to spawn multiple instances of the same job type, then this will
 be the starting port number since fio will use a range of ports.

 [netsplice] interface=str
 [net] interface=str  The IP address of the network interface used to send or
 		receive UDP multicast

 [netsplice] ttl=int
 [net] ttl=int	Time-to-live value for outgoing UDP multicast packets.
 		Default: 1

 [netsplice] nodelay=bool
 [net] nodelay=bool	Set TCP_NODELAY on TCP connections.

 [netsplice] protocol=str
 [netsplice] proto=str
 [net] protocol=str
 [net] proto=str	The network protocol to use. Accepted values are:

 			tcp	Transmission control protocol
 			tcpv6	Transmission control protocol V6
 			udp	User datagram protocol
 			udpv6	User datagram protocol V6
 			unix	UNIX domain socket

 		When the protocol is TCP or UDP, the port must also be given,
 		as well as the hostname if the job is a TCP listener or UDP
 		reader. For unix sockets, the normal filename option should be
 		used and the port is invalid.

 [net] listen	For TCP network connections, tell fio to listen for incoming
 		connections rather than initiating an outgoing connection. The
 		hostname must be omitted if this option is used.

 [net] pingpong	Normaly a network writer will just continue writing data, and
 		a network reader will just consume packages. If pingpong=1
 		is set, a writer will send its normal payload to the reader,
 		then wait for the reader to send the same payload back. This
 		allows fio to measure network latencies. The submission
 		and completion latencies then measure local time spent
 		sending or receiving, and the completion latency measures
 		how long it took for the other end to receive and send back.
 		For UDP multicast traffic pingpong=1 should only be set for a
 		single reader when multiple readers are listening to the same
 		address.

 [net] window_size	Set the desired socket buffer size for the connection.

 [net] mss	Set the TCP maximum segment size (TCP_MAXSEG).

 [e4defrag] donorname=str
 	        File will be used as a block donor(swap extents between files)
 [e4defrag] inplace=int
 		Configure donor file blocks allocation strategy
 		0(default): Preallocate donor's file on init
 		1 	  : allocate space immidietly inside defragment event,
 			    and free right after event


 6.0 Interpreting the output
 ---------------------------

 fio spits out a lot of output. While running, fio will display the
 status of the jobs created. An example of that would be:

 Threads: 1: [_r] [24.8% done] [ 13509/  8334 kb/s] [eta 00h:01m:31s]

 The characters inside the square brackets denote the current status of
 each thread. The possible values (in typical life cycle order) are:

 Idle	Run
 ----    ---
 P		Thread setup, but not started.
 C		Thread created.
 I		Thread initialized, waiting or generating necessary data.
 	p	Thread running pre-reading file(s).
 	R	Running, doing sequential reads.
 	r	Running, doing random reads.
 	W	Running, doing sequential writes.
 	w	Running, doing random writes.
 	M	Running, doing mixed sequential reads/writes.
 	m	Running, doing mixed random reads/writes.
 	F	Running, currently waiting for fsync()
 	f	Running, finishing up (writing IO logs, etc)
 	V	Running, doing verification of written data.
 E		Thread exited, not reaped by main thread yet.
 _		Thread reaped, or
 X		Thread reaped, exited with an error.
 K		Thread reaped, exited due to signal.

 Fio will condense the thread string as not to take up more space on the
 command line as is needed. For instance, if you have 10 readers and 10
 writers running, the output would look like this:

 Jobs: 20 (f=20): [R(10),W(10)] [4.0% done] [2103MB/0KB/0KB /s] [538K/0/0 iops] [eta 57m:36s]

 Fio will still maintain the ordering, though. So the above means that jobs
 1..10 are readers, and 11..20 are writers.

 The other values are fairly self explanatory - number of threads
 currently running and doing io, rate of io since last check (read speed
 listed first, then write speed), and the estimated completion percentage
 and time for the running group. It's impossible to estimate runtime of
 the following groups (if any). Note that the string is displayed in order,
 so it's possible to tell which of the jobs are currently doing what. The
 first character is the first job defined in the job file, and so forth.

 When fio is done (or interrupted by ctrl-c), it will show the data for
 each thread, group of threads, and disks in that order. For each data
 direction, the output looks like:

 Client1 (g=0): err= 0:
   write: io=    32MB, bw=   666KB/s, iops=89 , runt= 50320msec
     slat (msec): min=    0, max=  136, avg= 0.03, stdev= 1.92
     clat (msec): min=    0, max=  631, avg=48.50, stdev=86.82
     bw (KB/s) : min=    0, max= 1196, per=51.00%, avg=664.02, stdev=681.68
   cpu        : usr=1.49%, sys=0.25%, ctx=7969, majf=0, minf=17
   IO depths    : 1=0.1%, 2=0.3%, 4=0.5%, 8=99.0%, 16=0.0%, 32=0.0%, >32=0.0%
      submit    : 0=0.0%, 4=100.0%, 8=0.0%, 16=0.0%, 32=0.0%, 64=0.0%, >=64=0.0%
      complete  : 0=0.0%, 4=100.0%, 8=0.0%, 16=0.0%, 32=0.0%, 64=0.0%, >=64=0.0%
      issued r/w: total=0/32768, short=0/0
      lat (msec): 2=1.6%, 4=0.0%, 10=3.2%, 20=12.8%, 50=38.4%, 100=24.8%,
      lat (msec): 250=15.2%, 500=0.0%, 750=0.0%, 1000=0.0%, >=2048=0.0%

 The client number is printed, along with the group id and error of that
 thread. Below is the io statistics, here for writes. In the order listed,
 they denote:

 io=		Number of megabytes io performed
 bw=		Average bandwidth rate
 iops=           Average IOs performed per second
 runt=		The runtime of that thread
 	slat=	Submission latency (avg being the average, stdev being the
 		standard deviation). This is the time it took to submit
 		the io. For sync io, the slat is really the completion
 		latency, since queue/complete is one operation there. This
 		value can be in milliseconds or microseconds, fio will choose
 		the most appropriate base and print that. In the example
 		above, milliseconds is the best scale. Note: in --minimal mode
 		latencies are always expressed in microseconds.
 	clat=	Completion latency. Same names as slat, this denotes the
 		time from submission to completion of the io pieces. For
 		sync io, clat will usually be equal (or very close) to 0,
 		as the time from submit to complete is basically just
 		CPU time (io has already been done, see slat explanation).
 	bw=	Bandwidth. Same names as the xlat stats, but also includes
 		an approximate percentage of total aggregate bandwidth
 		this thread received in this group. This last value is
 		only really useful if the threads in this group are on the
 		same disk, since they are then competing for disk access.
 cpu=		CPU usage. User and system time, along with the number
 		of context switches this thread went through, usage of
 		system and user time, and finally the number of major
 		and minor page faults.
 IO depths=	The distribution of io depths over the job life time. The
 		numbers are divided into powers of 2, so for example the
 		16= entries includes depths up to that value but higher
 		than the previous entry. In other words, it covers the
 		range from 16 to 31.
 IO submit=	How many pieces of IO were submitting in a single submit
 		call. Each entry denotes that amount and below, until
 		the previous entry - eg, 8=100% mean that we submitted
 		anywhere in between 5-8 ios per submit call.
 IO complete=	Like the above submit number, but for completions instead.
 IO issued=	The number of read/write requests issued, and how many
 		of them were short.
 IO latencies=	The distribution of IO completion latencies. This is the
 		time from when IO leaves fio and when it gets completed.
 		The numbers follow the same pattern as the IO depths,
 		meaning that 2=1.6% means that 1.6% of the IO completed
 		within 2 msecs, 20=12.8% means that 12.8% of the IO
 		took more than 10 msecs, but less than (or equal to) 20 msecs.

 After each client has been listed, the group statistics are printed. They
 will look like this:

 Run status group 0 (all jobs):
    READ: io=64MB, aggrb=22178, minb=11355, maxb=11814, mint=2840msec, maxt=2955msec
   WRITE: io=64MB, aggrb=1302, minb=666, maxb=669, mint=50093msec, maxt=50320msec

 For each data direction, it prints:

 io=		Number of megabytes io performed.
 aggrb=		Aggregate bandwidth of threads in this group.
 minb=		The minimum average bandwidth a thread saw.
 maxb=		The maximum average bandwidth a thread saw.
 mint=		The smallest runtime of the threads in that group.
 maxt=		The longest runtime of the threads in that group.

 And finally, the disk statistics are printed. They will look like this:

 Disk stats (read/write):
   sda: ios=16398/16511, merge=30/162, ticks=6853/819634, in_queue=826487, util=100.00%

 Each value is printed for both reads and writes, with reads first. The
 numbers denote:

 ios=		Number of ios performed by all groups.
 merge=		Number of merges io the io scheduler.
 ticks=		Number of ticks we kept the disk busy.
 io_queue=	Total time spent in the disk queue.
 util=		The disk utilization. A value of 100% means we kept the disk
 		busy constantly, 50% would be a disk idling half of the time.

 It is also possible to get fio to dump the current output while it is
 running, without terminating the job. To do that, send fio the USR1 signal.
 You can also get regularly timed dumps by using the --status-interval
 parameter, or by creating a file in /tmp named fio-dump-status. If fio
 sees this file, it will unlink it and dump the current output status.


 7.0 Terse output
 ----------------

 For scripted usage where you typically want to generate tables or graphs
 of the results, fio can output the results in a semicolon separated format.
 The format is one long line of values, such as:

 2;card0;0;0;7139336;121836;60004;1;10109;27.932460;116.933948;220;126861;3495.446807;1085.368601;226;126864;3523.635629;1089.012448;24063;99944;50.275485%;59818.274627;5540.657370;7155060;122104;60004;1;8338;29.086342;117.839068;388;128077;5032.488518;1234.785715;391;128085;5061.839412;1236.909129;23436;100928;50.287926%;59964.832030;5644.844189;14.595833%;19.394167%;123706;0;7313;0.1%;0.1%;0.1%;0.1%;0.1%;0.1%;100.0%;0.00%;0.00%;0.00%;0.00%;0.00%;0.00%;0.01%;0.02%;0.05%;0.16%;6.04%;40.40%;52.68%;0.64%;0.01%;0.00%;0.01%;0.00%;0.00%;0.00%;0.00%;0.00%
 A description of this job goes here.

 The job description (if provided) follows on a second line.

 To enable terse output, use the --minimal command line option. The first
 value is the version of the terse output format. If the output has to
 be changed for some reason, this number will be incremented by 1 to
 signify that change.

 Split up, the format is as follows:

 	terse version, fio version, jobname, groupid, error
 	READ status:
 		Total IO (KB), bandwidth (KB/sec), IOPS, runtime (msec)
 		Submission latency: min, max, mean, deviation (usec)
 		Completion latency: min, max, mean, deviation (usec)
 		Completion latency percentiles: 20 fields (see below)
 		Total latency: min, max, mean, deviation (usec)
 		Bw (KB/s): min, max, aggregate percentage of total, mean, deviation
 	WRITE status:
 		Total IO (KB), bandwidth (KB/sec), IOPS, runtime (msec)
 		Submission latency: min, max, mean, deviation (usec)
 		Completion latency: min, max, mean, deviation (usec)
 		Completion latency percentiles: 20 fields (see below)
 		Total latency: min, max, mean, deviation (usec)
 		Bw (KB/s): min, max, aggregate percentage of total, mean, deviation
 	CPU usage: user, system, context switches, major faults, minor faults
 	IO depths: <=1, 2, 4, 8, 16, 32, >=64
 	IO latencies microseconds: <=2, 4, 10, 20, 50, 100, 250, 500, 750, 1000
 	IO latencies milliseconds: <=2, 4, 10, 20, 50, 100, 250, 500, 750, 1000, 2000, >=2000
 	Disk utilization: Disk name, Read ios, write ios,
 			  Read merges, write merges,
 			  Read ticks, write ticks,
 			  Time spent in queue, disk utilization percentage
 	Additional Info (dependent on continue_on_error, default off): total # errors, first error code

 	Additional Info (dependent on description being set): Text description

 Completion latency percentiles can be a grouping of up to 20 sets, so
 for the terse output fio writes all of them. Each field will look like this:

 	1.00%=6112

 which is the Xth percentile, and the usec latency associated with it.

 For disk utilization, all disks used by fio are shown. So for each disk
 there will be a disk utilization section.


 8.0 Trace file format
 ---------------------
 There are two trace file format that you can encounter. The older (v1) format
 is unsupported since version 1.20-rc3 (March 2008). It will still be described
 below in case that you get an old trace and want to understand it.

 In any case the trace is a simple text file with a single action per line.


 8.1 Trace file format v1
 ------------------------
 Each line represents a single io action in the following format:

 rw, offset, length

 where rw=0/1 for read/write, and the offset and length entries being in bytes.

 This format is not supported in Fio versions => 1.20-rc3.


 8.2 Trace file format v2
 ------------------------
 The second version of the trace file format was added in Fio version 1.17.
 It allows to access more then one file per trace and has a bigger set of
 possible file actions.

 The first line of the trace file has to be:

 fio version 2 iolog

 Following this can be lines in two different formats, which are described below.

 The file management format:

 filename action

 The filename is given as an absolute path. The action can be one of these:

 add          Add the given filename to the trace
 open         Open the file with the given filename. The filename has to have
              been added with the add action before.
 close        Close the file with the given filename. The file has to have been
              opened before.


 The file io action format:

 filename action offset length

 The filename is given as an absolute path, and has to have been added and opened
 before it can be used with this format. The offset and length are given in
 bytes. The action can be one of these:

 wait       Wait for 'offset' microseconds. Everything below 100 is discarded.
 read       Read 'length' bytes beginning from 'offset'
 write      Write 'length' bytes beginning from 'offset'
 sync       fsync() the file
 datasync   fdatasync() the file
 trim       trim the given file from the given 'offset' for 'length' bytes


 9.0 CPU idleness profiling
 --------------------------
 In some cases, we want to understand CPU overhead in a test. For example,
 we test patches for the specific goodness of whether they reduce CPU usage.
 fio implements a balloon approach to create a thread per CPU that runs at
 idle priority, meaning that it only runs when nobody else needs the cpu.
 By measuring the amount of work completed by the thread, idleness of each
 CPU can be derived accordingly.

 An unit work is defined as touching a full page of unsigned characters. Mean
 and standard deviation of time to complete an unit work is reported in "unit
 work" section. Options can be chosen to report detailed percpu idleness or
 overall system idleness by aggregating percpu stats.