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48 lines
1.7 KiB
48 lines
1.7 KiB
4 months ago
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Demonstrations of mdflush, the Linux eBPF/bcc version.
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The mdflush tool traces flushes at the md driver level, and prints details
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including the time of the flush:
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# ./mdflush
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Tracing md flush requests... Hit Ctrl-C to end.
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TIME PID COMM DEVICE
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03:13:49 16770 sync md0
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03:14:08 16864 sync md0
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03:14:49 496 kworker/1:0H md0
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03:14:49 488 xfsaild/md0 md0
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03:14:54 488 xfsaild/md0 md0
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03:15:00 488 xfsaild/md0 md0
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03:15:02 85 kswapd0 md0
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03:15:02 488 xfsaild/md0 md0
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03:15:05 488 xfsaild/md0 md0
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03:15:08 488 xfsaild/md0 md0
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03:15:10 488 xfsaild/md0 md0
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03:15:11 488 xfsaild/md0 md0
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03:15:11 488 xfsaild/md0 md0
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03:15:11 488 xfsaild/md0 md0
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03:15:11 488 xfsaild/md0 md0
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03:15:11 488 xfsaild/md0 md0
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03:15:12 488 xfsaild/md0 md0
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03:15:13 488 xfsaild/md0 md0
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03:15:15 488 xfsaild/md0 md0
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03:15:19 496 kworker/1:0H md0
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03:15:49 496 kworker/1:0H md0
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03:15:55 18840 sync md0
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03:16:49 496 kworker/1:0H md0
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03:17:19 496 kworker/1:0H md0
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03:20:19 496 kworker/1:0H md0
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03:21:19 496 kworker/1:0H md0
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03:21:49 496 kworker/1:0H md0
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03:25:19 496 kworker/1:0H md0
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[...]
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This can be useful for correlation with latency outliers or spikes in disk
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latency, as measured using another tool (eg, system monitoring). If spikes in
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disk latency often coincide with md flush events, then it would make flushing
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a target for tuning.
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Note that the flush events are likely to originate from higher in the I/O
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stack, such as from file systems. This traces md processing them, and the
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timestamp corresponds with when md began to issue the flush to disks.
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