tools/biolatpcts_example.txt

Demonstrations of biolatpcts, the Linux eBPF/bcc version.


biolatpcts traces block device I/O (disk I/O), and prints the latency
percentiles per I/O type. Example:

# ./biolatpcts.py /dev/nvme0n1
nvme0n1    p1    p5   p10   p16   p25   p50   p75   p84   p90   p95   p99  p100
read     95us 175us 305us 515us 895us 985us 995us 1.5ms 2.5ms 3.5ms 4.5ms  10ms
write     5us   5us   5us  15us  25us 135us 765us 855us 885us 895us 965us 1.5ms
discard   5us   5us   5us   5us 135us 145us 165us 205us 385us 875us 1.5ms 2.5ms
flush     5us   5us   5us   5us   5us   5us   5us   5us   5us 1.5ms 4.5ms 5.5ms
[...]

Unless changed with the -i option, the latency percentiles are printed every 3
seconds.


Any number of custom percentiles can be requested with the -p option:

# ./biolatpcts.py /dev/nvme0n1 -p 01,90.0,99.9,99.99,100.0

nvme0n1    01  90.0  99.9 99.99 100.0
read      5us 4.5ms  16ms  22ms  26ms
write    15us 255us 365us 515us 2.5ms
discard     -     -     -     -     -
flush     5us   5us   5us   5us  24ms
[...]

Note that the target percentile strings are preserved as-is to facilitate
exact key matching when the output is consumed by another program.


When the output is consumed by another program, parsing can be tedious. The -j
option makes biolatpcts output results in json, one line per interval.

# ./tools/biolatpcts.py /dev/nvme0n1 -j
{"read": {"1": 2.5e-05, "5": 3.5e-05, "10": 4.5e-05, "16": 0.000145, "25": 0.000195, "50": 0.000355, "75": 0.000605, "84": 0.000775, "90": 0.000965, "95": 0.0015, "99": 0.0025, "100": 0.0235}, "write": {"1": 5e-06, "5": 5e-06, "10": 5e-06, "16": 5e-06, "25": 1.5e-05, "50": 2.5e-05, "75": 4.5e-05, "84": 7.5e-05, "90": 0.000195, "95": 0.000665, "99": 0.0015, "100": 0.0035}, "discard": {"1": 0.0, "5": 0.0, "10": 0.0, "16": 0.0, "25": 0.0, "50": 0.0, "75": 0.0, "84": 0.0, "90": 0.0, "95": 0.0, "99": 0.0, "100": 0.0}, "flush": {"1": 0.0, "5": 0.0, "10": 0.0, "16": 0.0, "25": 0.0, "50": 0.0, "75": 0.0, "84": 0.0, "90": 0.0, "95": 0.0, "99": 0.0, "100": 0.0}}
[...]


By default biolatpcts measures the duration each IO was on the device. It can
be changed using the -w option.


USAGE message:

usage: biolatpcts.py [-h] [-i INTERVAL]
                     [-w {from-rq-alloc,after-rq-alloc,on-device}]
                     [-p PCT,...] [-j] [--verbose]
                     DEV

Monitor IO latency distribution of a block device

positional arguments:
  DEV                   Target block device (/dev/DEVNAME, DEVNAME or MAJ:MIN)

optional arguments:
  -h, --help            show this help message and exit
  -i INTERVAL, --interval INTERVAL
                        Report interval (default: 3)
  -w {from-rq-alloc,after-rq-alloc,on-device}, --which {from-rq-alloc,after-rq-alloc,on-device}
                        Which latency to measure (default: on-device)
  -p PCT,..., --pcts PCT,...
                        Percentiles to calculate (default:
                        1,5,10,16,25,50,75,84,90,95,99,100)
  -j, --json            Output in json (default: False)
  --verbose, -v