NAME¶

vfscount - Count VFS calls ("vfs_*"). Uses Linux eBPF/bcc.

SYNOPSIS¶

vfscount [duration]

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.

REQUIREMENTS¶

CONFIG_BPF and bcc.

OPTIONS¶

duration

duration of the trace in seconds.

EXAMPLES¶

Count some VFS calls until Ctrl-C is hit:

# vfscount

Count some VFS calls in ten seconds

# vfscount 10

FIELDS¶

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).

FUNC

Kernel function name

COUNT

Number of calls while tracing

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_").

SOURCE¶

This is from bcc.

https://github.com/iovisor/bcc

Also look in the bcc distribution for a companion _examples.txt file containing example usage, output, and commentary for this tool.

OS¶

Linux

AUTHOR¶

Brendan Gregg

SEE ALSO¶

vfsstat(8)