1 Demonstrations of mdflush, the Linux eBPF/bcc version. 2 3 4 The mdflush tool traces flushes at the md driver level, and prints details 5 including the time of the flush: 6 7 # ./mdflush 8 Tracing md flush requests... Hit Ctrl-C to end. 9 TIME PID COMM DEVICE 10 03:13:49 16770 sync md0 11 03:14:08 16864 sync md0 12 03:14:49 496 kworker/1:0H md0 13 03:14:49 488 xfsaild/md0 md0 14 03:14:54 488 xfsaild/md0 md0 15 03:15:00 488 xfsaild/md0 md0 16 03:15:02 85 kswapd0 md0 17 03:15:02 488 xfsaild/md0 md0 18 03:15:05 488 xfsaild/md0 md0 19 03:15:08 488 xfsaild/md0 md0 20 03:15:10 488 xfsaild/md0 md0 21 03:15:11 488 xfsaild/md0 md0 22 03:15:11 488 xfsaild/md0 md0 23 03:15:11 488 xfsaild/md0 md0 24 03:15:11 488 xfsaild/md0 md0 25 03:15:11 488 xfsaild/md0 md0 26 03:15:12 488 xfsaild/md0 md0 27 03:15:13 488 xfsaild/md0 md0 28 03:15:15 488 xfsaild/md0 md0 29 03:15:19 496 kworker/1:0H md0 30 03:15:49 496 kworker/1:0H md0 31 03:15:55 18840 sync md0 32 03:16:49 496 kworker/1:0H md0 33 03:17:19 496 kworker/1:0H md0 34 03:20:19 496 kworker/1:0H md0 35 03:21:19 496 kworker/1:0H md0 36 03:21:49 496 kworker/1:0H md0 37 03:25:19 496 kworker/1:0H md0 38 [...] 39 40 This can be useful for correlation with latency outliers or spikes in disk 41 latency, as measured using another tool (eg, system monitoring). If spikes in 42 disk latency often coincide with md flush events, then it would make flushing 43 a target for tuning. 44 45 Note that the flush events are likely to originate from higher in the I/O 46 stack, such as from file systems. This traces md processing them, and the 47 timestamp corresponds with when md began to issue the flush to disks. 48
