.TH vfscount 8  "2015-08-18" "USER COMMANDS"
.SH NAME
vfscount \- Count VFS calls ("vfs_*"). Uses Linux eBPF/bcc.
.SH SYNOPSIS
.B vfscount
.SH DESCRIPTION
This counts VFS calls. This can be useful for general workload
characterization of these operations.

This works by tracing all kernel functions beginning with "vfs_" using dynamic
tracing. This may match more functions than you are interested in measuring:
Edit the script to customize which functions to trace.

Since this uses BPF, only the root user can use this tool.
.SH REQUIREMENTS
CONFIG_BPF and bcc.
.SH EXAMPLES
.TP
Count some VFS calls until Ctrl-C is hit:
#
.B vfscount
.SH FIELDS
.TP
ADDR
Address of the instruction pointer that was traced (only useful if the FUNC column is suspicious and you would like to double check the translation).
.TP
FUNC
Kernel function name
.TP
COUNT
Number of calls while tracing
.SH OVERHEAD
This traces kernel vfs functions and maintains in-kernel counts, which
are asynchronously copied to user-space. While the rate of VFS operations can
be very high (>1M/sec), this is a relatively efficient way to trace these
events, and so the overhead is expected to be small for normal workloads.
Measure in a test environment, and if overheads are an issue, edit the script
to reduce the types of vfs functions traced (currently all beginning with
"vfs_").
.SH SOURCE
This is from bcc.
.IP
https://github.com/iovisor/bcc
.PP
Also look in the bcc distribution for a companion _examples.txt file containing
example usage, output, and commentary for this tool.
.SH OS
Linux
.SH STABILITY
Unstable - in development.
.SH AUTHOR
Brendan Gregg
.SH SEE ALSO
vfsstat(8)