runqlen_example.txt

Demonstrations of runqlen, the Linux BPF/bpftrace version.


This tool samples the length of the CPU scheduler run queues, showing these
sampled lengths as a histogram. This can be used to characterize demand for
CPU resources. For example:

# ./runqlen.bt 
Attaching 2 probes...
Sampling run queue length at 99 Hertz... Hit Ctrl-C to end.
^C

@runqlen: 
[0, 1)              1967 |@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@|
[1, 2)                 0 |                                                    |
[2, 3)                 0 |                                                    |
[3, 4)               306 |@@@@@@@@                                            |

This output shows that the run queue length was usually zero, except for some
samples where it was 3. This was caused by binding 4 CPU bound threads to a
single CPUs.


There is another version of this tool in bcc: https://github.com/iovisor/bcc
The bcc version provides options to customize the output.