Current File : //usr/share/doc/bpftrace/examples/biosnoop_example.txt
Demonstrations of biosnoop, the Linux BPF/bpftrace version.
This traces block I/O, and shows the issuing process (at least, the process
that was on-CPU at the time of queue insert) and the latency of the I/O:
# ./biosnoop.bt
Attaching 4 probes...
TIME(ms) DISK COMM PID LAT(ms)
611 nvme0n1 bash 4179 10
611 nvme0n1 cksum 4179 0
627 nvme0n1 cksum 4179 15
641 nvme0n1 cksum 4179 13
644 nvme0n1 cksum 4179 3
658 nvme0n1 cksum 4179 13
673 nvme0n1 cksum 4179 14
686 nvme0n1 cksum 4179 13
701 nvme0n1 cksum 4179 14
710 nvme0n1 cksum 4179 8
717 nvme0n1 cksum 4179 6
728 nvme0n1 cksum 4179 10
735 nvme0n1 cksum 4179 6
751 nvme0n1 cksum 4179 10
758 nvme0n1 cksum 4179 17
783 nvme0n1 cksum 4179 12
796 nvme0n1 cksum 4179 25
802 nvme0n1 cksum 4179 32
[...]
This output shows the cksum process was issuing block I/O, which were
completing with around 12 milliseconds of latency. Each block I/O event is
printed out, with a completion time as the first column, measured from
program start.
An example of some background flushing:
# ./biosnoop.bt
Attaching 4 probes...
TIME(ms) DISK COMM PID LAT(ms)
2966 nvme0n1 jbd2/nvme0n1-8 615 0
2967 nvme0n1 jbd2/nvme0n1-8 615 0
[...]
There is another version of this tool in bcc: https://github.com/iovisor/bcc
The bcc version provides more fields.
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