| Demonstrations of zfsdist, the Linux eBPF/bcc version. |
| |
| |
| zfsdist traces ZFS reads, writes, opens, and fsyncs, and summarizes their |
| latency as a power-of-2 histogram. It has been written to work on ZFS on Linux |
| (http://zfsonlinux.org). For example: |
| |
| # ./zfsdist |
| Tracing ZFS operation latency... Hit Ctrl-C to end. |
| ^C |
| |
| operation = 'read' |
| usecs : count distribution |
| 0 -> 1 : 0 | | |
| 2 -> 3 : 0 | | |
| 4 -> 7 : 4479 |****************************************| |
| 8 -> 15 : 1028 |********* | |
| 16 -> 31 : 14 | | |
| 32 -> 63 : 1 | | |
| 64 -> 127 : 2 | | |
| 128 -> 255 : 6 | | |
| 256 -> 511 : 1 | | |
| 512 -> 1023 : 1256 |*********** | |
| 1024 -> 2047 : 9 | | |
| 2048 -> 4095 : 1 | | |
| 4096 -> 8191 : 2 | | |
| |
| operation = 'write' |
| usecs : count distribution |
| 0 -> 1 : 0 | | |
| 2 -> 3 : 0 | | |
| 4 -> 7 : 0 | | |
| 8 -> 15 : 0 | | |
| 16 -> 31 : 0 | | |
| 32 -> 63 : 0 | | |
| 64 -> 127 : 0 | | |
| 128 -> 255 : 75 |****************************************| |
| 256 -> 511 : 11 |***** | |
| 512 -> 1023 : 0 | | |
| 1024 -> 2047 : 0 | | |
| 2048 -> 4095 : 0 | | |
| 4096 -> 8191 : 0 | | |
| 8192 -> 16383 : 0 | | |
| 16384 -> 32767 : 0 | | |
| 32768 -> 65535 : 0 | | |
| 65536 -> 131071 : 13 |****** | |
| 131072 -> 262143 : 1 | | |
| |
| operation = 'open' |
| usecs : count distribution |
| 0 -> 1 : 0 | | |
| 2 -> 3 : 2 |****************************************| |
| |
| This output shows a bimodal distribution for read latency, with a faster |
| mode of around 5 thousand reads that took between 4 and 15 microseconds, and a |
| slower mode of 1256 reads that took between 512 and 1023 microseconds. It's |
| likely that the faster mode was a hit from the in-memory file system cache, |
| and the slower mode is a read from a storage device (disk). |
| |
| The write latency is also bimodal, with a faster mode between 128 and 511 us, |
| and the slower mode between 65 and 131 ms. |
| |
| This "latency" is measured from when the operation was issued from the VFS |
| interface to the file system (via the ZFS POSIX layer), to when it completed. |
| This spans everything: block device I/O (disk I/O), file system CPU cycles, |
| file system locks, run queue latency, etc. This is a better measure of the |
| latency suffered by applications reading from the file system than measuring |
| this down at the block device interface. |
| |
| Note that this only traces the common file system operations previously |
| listed: other file system operations (eg, inode operations including |
| getattr()) are not traced. |
| |
| |
| An optional interval and a count can be provided, as well as -m to show the |
| distributions in milliseconds. For example: |
| |
| # ./zfsdist 1 5 |
| Tracing ZFS operation latency... Hit Ctrl-C to end. |
| |
| 06:55:41: |
| |
| operation = 'read' |
| usecs : count distribution |
| 0 -> 1 : 0 | | |
| 2 -> 3 : 0 | | |
| 4 -> 7 : 3976 |****************************************| |
| 8 -> 15 : 1181 |*********** | |
| 16 -> 31 : 18 | | |
| 32 -> 63 : 4 | | |
| 64 -> 127 : 17 | | |
| 128 -> 255 : 16 | | |
| 256 -> 511 : 0 | | |
| 512 -> 1023 : 1275 |************ | |
| 1024 -> 2047 : 36 | | |
| 2048 -> 4095 : 3 | | |
| 4096 -> 8191 : 0 | | |
| 8192 -> 16383 : 1 | | |
| 16384 -> 32767 : 1 | | |
| |
| 06:55:42: |
| |
| operation = 'read' |
| usecs : count distribution |
| 0 -> 1 : 0 | | |
| 2 -> 3 : 0 | | |
| 4 -> 7 : 12751 |****************************************| |
| 8 -> 15 : 1190 |*** | |
| 16 -> 31 : 38 | | |
| 32 -> 63 : 7 | | |
| 64 -> 127 : 85 | | |
| 128 -> 255 : 47 | | |
| 256 -> 511 : 0 | | |
| 512 -> 1023 : 1010 |*** | |
| 1024 -> 2047 : 49 | | |
| 2048 -> 4095 : 12 | | |
| |
| 06:55:43: |
| |
| operation = 'read' |
| usecs : count distribution |
| 0 -> 1 : 0 | | |
| 2 -> 3 : 0 | | |
| 4 -> 7 : 80925 |****************************************| |
| 8 -> 15 : 1645 | | |
| 16 -> 31 : 251 | | |
| 32 -> 63 : 24 | | |
| 64 -> 127 : 16 | | |
| 128 -> 255 : 12 | | |
| 256 -> 511 : 0 | | |
| 512 -> 1023 : 80 | | |
| 1024 -> 2047 : 1 | | |
| |
| 06:55:44: |
| |
| operation = 'read' |
| usecs : count distribution |
| 0 -> 1 : 0 | | |
| 2 -> 3 : 0 | | |
| 4 -> 7 : 81207 |****************************************| |
| 8 -> 15 : 2075 |* | |
| 16 -> 31 : 2005 | | |
| 32 -> 63 : 177 | | |
| 64 -> 127 : 3 | | |
| |
| 06:55:45: |
| |
| operation = 'read' |
| usecs : count distribution |
| 0 -> 1 : 0 | | |
| 2 -> 3 : 0 | | |
| 4 -> 7 : 74364 |****************************************| |
| 8 -> 15 : 865 | | |
| 16 -> 31 : 4960 |** | |
| 32 -> 63 : 625 | | |
| 64 -> 127 : 2 | | |
| |
| This workload was randomly reading from a file that became cached. The slower |
| mode can be seen to disappear by the final summaries. |
| |
| |
| USAGE message: |
| |
| # ./zfsdist -h |
| usage: zfsdist [-h] [-T] [-m] [-p PID] [interval] [count] |
| |
| Summarize ZFS operation latency |
| |
| positional arguments: |
| interval output interval, in seconds |
| count number of outputs |
| |
| optional arguments: |
| -h, --help show this help message and exit |
| -T, --notimestamp don't include timestamp on interval output |
| -m, --milliseconds output in milliseconds |
| -p PID, --pid PID trace this PID only |
| |
| examples: |
| ./zfsdist # show operation latency as a histogram |
| ./zfsdist -p 181 # trace PID 181 only |
| ./zfsdist 1 10 # print 1 second summaries, 10 times |
| ./zfsdist -m 5 # 5s summaries, milliseconds |