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 la‐
       tency.

       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/iovisor/bpftrace

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

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

              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)