1pidpersec(8) System Manager's Manual pidpersec(8)
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6 mdflush - Trace md flush events. Uses Linux eBPF/bcc.
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9 mdflush
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12 This tool traces flush events by md, the Linux multiple device driver
13 (software RAID). The timestamp and md device for the flush are printed.
14 Knowing when these flushes happen can be useful for correlation with
15 unexplained spikes in disk latency.
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17 This works by tracing the kernel md_flush_request() function using
18 dynamic tracing, and will need updating to match any changes to this
19 function.
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21 Note that the flushes themselves are likely to originate from higher in
22 the I/O stack, such as from the file systems.
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24 Since this uses BPF, only the root user can use this tool.
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27 CONFIG_BPF and bcc.
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30 Trace md flush events:
31 # mdflush
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34 TIME Time of the flush event (HH:MM:SS).
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36 PID The process ID that was on-CPU when the event was issued. This
37 may identify the cause of the flush (eg, the "sync" command),
38 but will often identify a kernel worker thread that was managing
39 I/O.
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41 COMM The command name for the PID.
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43 DEVICE The md device name.
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46 Expected to be negligible.
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49 This is from bcc.
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51 https://github.com/iovisor/bcc
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53 Also look in the bcc distribution for a companion _examples.txt file
54 containing example usage, output, and commentary for this tool.
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57 Linux
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60 Unstable - in development.
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63 Brendan Gregg
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66 biosnoop(8)
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70USER COMMANDS 2016-02-13 pidpersec(8)