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vfsreadlat_example.txt
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vfsreadlat_example.txt
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Demonstrations of vfsreadlat.py, the Linux eBPF/bcc version.
This example traces the latency of vfs_read (time from call to return), printing
it as a histogram distribution. By default, output is every five seconds:
# ./vfsreadlat.py
Tracing... Hit Ctrl-C to end.
usecs : count distribution
0 -> 1 : 4457 |*************************************+|
2 -> 3 : 447 |*** |
4 -> 7 : 2059 |***************** |
8 -> 15 : 1179 |********** |
16 -> 31 : 63 | |
32 -> 63 : 0 | |
64 -> 127 : 2 | |
128 -> 255 : 0 | |
256 -> 511 : 3 | |
512 -> 1023 : 1 | |
1024 -> 2047 : 3 | |
2048 -> 4095 : 2 | |
4096 -> 8191 : 0 | |
8192 -> 16383 : 0 | |
16384 -> 32767 : 0 | |
32768 -> 65535 : 0 | |
65536 -> 131071 : 4 | |
131072 -> 262143 : 2 | |
262144 -> 524287 : 0 | |
524288 -> 1048575 : 4 | |
^C
usecs : count distribution
0 -> 1 : 241 |*************************************+|
2 -> 3 : 17 |** |
4 -> 7 : 2 | |
8 -> 15 : 4 | |
16 -> 31 : 2 | |
32 -> 63 : 0 | |
64 -> 127 : 1 | |
128 -> 255 : 0 | |
256 -> 511 : 1 | |
512 -> 1023 : 1 | |
1024 -> 2047 : 0 | |
2048 -> 4095 : 1 | |
4096 -> 8191 : 0 | |
8192 -> 16383 : 0 | |
16384 -> 32767 : 0 | |
32768 -> 65535 : 0 | |
65536 -> 131071 : 0 | |
131072 -> 262143 : 0 | |
262144 -> 524287 : 0 | |
524288 -> 1048575 : 1 | |
These examples show outliers in the 524 - 1048 milliseconds range. Since
vfs_read() will catch many types of events, this could be anything including
keystroke latency on ssh sessions. Further drilling with bcc will be necessary
to identify more details.
Full usage:
# ./vfsreadlat.py -h
USAGE: ./vfsreadlat.py [interval [count]]