NAME

       mdflush - Trace md flush events. Uses Linux eBPF/bcc.

SYNOPSIS

       mdflush

DESCRIPTION

       This tool traces flush events by md, the Linux multiple device driver (software RAID). The
       timestamp and md device for the flush are printed.  Knowing when these flushes happen  can
       be useful for correlation with unexplained spikes in disk latency.

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

       Note that the flushes themselves are likely to originate from higher  in  the  I/O  stack,
       such as from the file systems.

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

REQUIREMENTS

       CONFIG_BPF and bcc.

EXAMPLES

       Trace md flush events:
              # mdflush

FIELDS

       TIME   Time of the flush event (HH:MM:SS).

       PID    The  process  ID  that  was on-CPU when the event was issued. This may identify the
              cause of the flush (eg, the "sync" command),  but  will  often  identify  a  kernel
              worker thread that was managing I/O.

       COMM   The command name for the PID.

       DEVICE The md device name.

OVERHEAD

       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

       biosnoop(8)