| .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) |
