1Demonstrations of vfsreadlat.py, the Linux eBPF/bcc version. 2 3 4This example traces the latency of vfs_read (time from call to return), printing 5it as a histogram distribution. By default, output is every five seconds: 6 7# ./vfsreadlat.py 8Tracing... Hit Ctrl-C to end. 9 10 usecs : count distribution 11 0 -> 1 : 4457 |*************************************+| 12 2 -> 3 : 447 |*** | 13 4 -> 7 : 2059 |***************** | 14 8 -> 15 : 1179 |********** | 15 16 -> 31 : 63 | | 16 32 -> 63 : 0 | | 17 64 -> 127 : 2 | | 18 128 -> 255 : 0 | | 19 256 -> 511 : 3 | | 20 512 -> 1023 : 1 | | 21 1024 -> 2047 : 3 | | 22 2048 -> 4095 : 2 | | 23 4096 -> 8191 : 0 | | 24 8192 -> 16383 : 0 | | 25 16384 -> 32767 : 0 | | 26 32768 -> 65535 : 0 | | 27 65536 -> 131071 : 4 | | 28 131072 -> 262143 : 2 | | 29 262144 -> 524287 : 0 | | 30 524288 -> 1048575 : 4 | | 31^C 32 usecs : count distribution 33 0 -> 1 : 241 |*************************************+| 34 2 -> 3 : 17 |** | 35 4 -> 7 : 2 | | 36 8 -> 15 : 4 | | 37 16 -> 31 : 2 | | 38 32 -> 63 : 0 | | 39 64 -> 127 : 1 | | 40 128 -> 255 : 0 | | 41 256 -> 511 : 1 | | 42 512 -> 1023 : 1 | | 43 1024 -> 2047 : 0 | | 44 2048 -> 4095 : 1 | | 45 4096 -> 8191 : 0 | | 46 8192 -> 16383 : 0 | | 47 16384 -> 32767 : 0 | | 48 32768 -> 65535 : 0 | | 49 65536 -> 131071 : 0 | | 50 131072 -> 262143 : 0 | | 51 262144 -> 524287 : 0 | | 52 524288 -> 1048575 : 1 | | 53 54These examples show outliers in the 524 - 1048 milliseconds range. Since 55vfs_read() will catch many types of events, this could be anything including 56keystroke latency on ssh sessions. Further drilling with bcc will be necessary 57to identify more details. 58 59 60Full usage: 61 62# ./vfsreadlat.py -h 63USAGE: ./vfsreadlat.py [interval [count]] 64