Manual: mdflush.bt

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

NAME
       mdflush.bt - Trace md flush events. Uses bpftrace/eBPF.

SYNOPSIS
       mdflush.bt

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 kernel 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 bpftrace.

EXAMPLES
       Trace md flush events:
	      # mdflush.bt

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 bpftrace.

	      https://github.com/bpftrace/bpftrace

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

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

	      https://github.com/iovisor/bcc

OS
       Linux

STABILITY
       Unstable - in development.

AUTHOR
       Brendan Gregg

SEE ALSO
       biosnoop.bt(8)

USER COMMANDS						 2018-09-07					       mdflush.bt(8)