| .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) |
