NAME¶

vfsstat.bt - Count key VFS calls. Uses bpftrace/eBPF.

SYNOPSIS¶

vfsstat.bt

DESCRIPTION¶

This traces some common VFS calls and prints per-second summaries. This can be useful for general workload characterization, and looking for patterns in operation usage over time.

This works by tracing some kernel vfs functions using dynamic tracing, and will need updating to match any changes to these functions. Edit the script to customize which functions are traced. Also see vfscount, which is more easily customized to trace multiple functions.

Since this uses BPF, only the root user can use this tool.

REQUIREMENTS¶

CONFIG_BPF and bpftrace.

EXAMPLES¶

Count some VFS calls, printing per-second summaries until Ctrl-C is hit:

# vfsstat.bt

FIELDS¶

HH:MM:SS

Each output summary is prefixed by the time of printing in "HH:MM:SS" format.

1st

Kernel function name (in @[])

2nd

Number of calls while tracing

OVERHEAD¶

This traces various 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.

SOURCE¶

This is from bpftrace.

https://github.com/iovisor/bpftrace

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

This is a bpftrace version of the bcc tool of the same name. The bcc tool may provide more options and customizations.

https://github.com/iovisor/bcc

OS¶

Linux

STABILITY¶

Unstable - in development.

AUTHOR¶

Brendan Gregg

SEE ALSO¶

vfscount.bt(8)