You can not select more than 25 topics
Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
58 lines
1.5 KiB
58 lines
1.5 KiB
.TH pidpersec 8 "2016-02-13" "USER COMMANDS"
|
|
.SH NAME
|
|
mdflush \- Trace md flush events. Uses Linux eBPF/bcc.
|
|
.SH SYNOPSIS
|
|
.B mdflush
|
|
.SH 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.
|
|
.SH REQUIREMENTS
|
|
CONFIG_BPF and bcc.
|
|
.SH EXAMPLES
|
|
.TP
|
|
Trace md flush events:
|
|
#
|
|
.B mdflush
|
|
.SH FIELDS
|
|
.TP
|
|
TIME
|
|
Time of the flush event (HH:MM:SS).
|
|
.TP
|
|
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.
|
|
.TP
|
|
COMM
|
|
The command name for the PID.
|
|
.TP
|
|
DEVICE
|
|
The md device name.
|
|
.SH OVERHEAD
|
|
Expected to be negligible.
|
|
.SH SOURCE
|
|
This is from bcc.
|
|
.IP
|
|
https://github.com/iovisor/bcc
|
|
.PP
|
|
Also look in the bcc distribution for a companion _examples.txt file containing
|
|
example usage, output, and commentary for this tool.
|
|
.SH OS
|
|
Linux
|
|
.SH STABILITY
|
|
Unstable - in development.
|
|
.SH AUTHOR
|
|
Brendan Gregg
|
|
.SH SEE ALSO
|
|
biosnoop(8)
|