Current File : //usr/share/doc/bpfcc-tools/examples/doc/biosnoop_example.txt
Demonstrations of biosnoop, the Linux eBPF/bcc version.
biosnoop traces block device I/O (disk I/O), and prints a line of output
per I/O. Example:
# ./biosnoop
TIME(s) COMM PID DISK T SECTOR BYTES LAT(ms)
0.000004 supervise 1950 xvda1 W 13092560 4096 0.74
0.000178 supervise 1950 xvda1 W 13092432 4096 0.61
0.001469 supervise 1956 xvda1 W 13092440 4096 1.24
0.001588 supervise 1956 xvda1 W 13115128 4096 1.09
1.022346 supervise 1950 xvda1 W 13115272 4096 0.98
1.022568 supervise 1950 xvda1 W 13188496 4096 0.93
1.023534 supervise 1956 xvda1 W 13188520 4096 0.79
1.023585 supervise 1956 xvda1 W 13189512 4096 0.60
2.003920 xfsaild/md0 456 xvdc W 62901512 8192 0.23
2.003931 xfsaild/md0 456 xvdb W 62901513 512 0.25
2.004034 xfsaild/md0 456 xvdb W 62901520 8192 0.35
2.004042 xfsaild/md0 456 xvdb W 63542016 4096 0.36
2.004204 kworker/0:3 26040 xvdb W 41950344 65536 0.34
2.044352 supervise 1950 xvda1 W 13192672 4096 0.65
2.044574 supervise 1950 xvda1 W 13189072 4096 0.58
This includes the PID and comm (process name) that were on-CPU at the time of
issue (which usually means the process responsible).
The latency of the disk I/O, measured from the issue to the device to its
completion, is included as the last column.
This example output is from what should be an idle system, however, the
following is visible in iostat:
$ iostat -x 1
[...]
avg-cpu: %user %nice %system %iowait %steal %idle
0.12 0.00 0.12 0.00 0.00 99.75
Device: rrqm/s wrqm/s r/s w/s rkB/s wkB/s await svctm %util
xvda 0.00 0.00 0.00 4.00 0.00 16.00 0.00 0.00 0.00
xvdb 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
xvdc 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
md0 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
There are 4 write IOPS.
The output of biosnoop identifies the reason: multiple supervise processes are
issuing writes to the xvda1 disk. I can now drill down on supervise using other
tools to understand its file system workload.
The -Q option includes a column to show the time spent queued in the OS:
# biosnoop.py -Q
TIME(s) COMM PID DISK T SECTOR BYTES QUE(ms) LAT(ms)
0.000000 kworker/u72:1 13379 nvme1n1 W 1142400 4096 0.01 0.55
0.000771 sync 22177 nvme1n1 W 41963894 3072 0.11 0.47
5.332998 xfsaild/nvme1n 1061 nvme1n1 W 545728 16384 0.01 0.61
5.333044 xfsaild/nvme1n 1061 nvme1n1 W 2349728 16384 0.02 0.64
5.333065 xfsaild/nvme1n 1061 nvme1n1 W 20971521 512 0.02 0.65
5.333067 xfsaild/nvme1n 1061 nvme1n1 W 20971528 8192 0.00 0.65
[...]
USAGE message:
usage: biosnoop.py [-h] [-Q] [-d DISK] [-P]
Trace block I/O
optional arguments:
-h, --help show this help message and exit
-Q, --queue include OS queued time
-d DISK, --disk DISK trace this disk only
-P, --pattern display block I/O pattern (sequential or random)
examples:
./biosnoop # trace all block I/O
./biosnoop -Q # include OS queued time
./biosnoop -d sdc # trace sdc only
./biosnoop -P # display block I/O pattern
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