runqlen.bt

#!/usr/bin/env bpftrace
// runqlen.bt	CPU scheduler run queue length as a histogram.
// 		For Linux, uses bpftrace, eBPF.
//
// Example of usage:
//
// # ./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.
//
// This is a bpftrace version of the bcc tool of the same name.
// The bcc version provides options to customize the output.
//
// Copyright 2018 Netflix, Inc.
//
// 07-Oct-2018	Brendan Gregg	Created this.

#ifndef BPFTRACE_HAVE_BTF
#include <linux/sched.h>

// Without BTF, we'll need to declare some of this struct manually,
// since it isn't available to be #included. This will need maintenance to match
// your kernel version. It is from kernel/sched/sched.h:
struct cfs_rq {
	struct load_weight load;
	unsigned int nr_queued;
	unsigned int h_nr_queued;
};
#endif

BEGIN
{
  printf("Sampling run queue length at 99 Hertz... Hit Ctrl-C to end.\n");
}

profile:hz:99
{
  $task = (struct task_struct *)curtask;
  $my_q = (struct cfs_rq *)$task.se.cfs_rq;
  $len = (uint64)$my_q.nr_queued;
  $len = ($len > 0) ? ($len - 1) : 0;
  // subtract currently running task
  @runqlen = lhist($len, 0, 100, 1);
}