Manual: mdflush-bpfcc

mdflush(8)					   System Manager's Manual					  mdflush(8)

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)

USER COMMANDS						 2016-02-13						  mdflush(8)