NAME

       syncsnoop - Trace sync() syscall. Uses Linux eBPF/bcc.

SYNOPSIS

       syncsnoop

DESCRIPTION

       syncsnoop  traces  calls  to sync(), which flushes file system buffers to storage devices.
       These calls can cause performance perturbations, and it can be useful to know if they  are
       happening and how frequently.

       This  works by tracing the kernel sys_sync() function using dynamic tracing, and will need
       updating to match any changes to this function.

       This makes use of a Linux 4.4 feature (bpf_perf_event_output()); for  kernels  older  than
       4.4, see the version under tools/old, which uses an older mechanism.

       This program is also a basic example of eBPF/bcc.

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

REQUIREMENTS

       CONFIG_BPF and bcc.

EXAMPLES

       Trace calls to sync():
              # syncsnoop

FIELDS

       TIME(s)
              Time of the call, in seconds.

       CALL   Call traced.

OVERHEAD

       This traces the kernel sync function and prints output for each event. As the rate of this
       is generally expected to  be  low  (<<  100/s),  the  overhead  is  also  expected  to  be
       negligible.

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

STABILITY

       Unstable - in development.

AUTHOR

       Brendan Gregg

SEE ALSO

       iostat(1)