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/usr/share/doc/bpftrace/examples

Name	Size	Mode	Actions
bashreadline_example.txt	722	0644	edit dl rm
biolatency_example.txt	1790	0644	edit dl rm
biosnoop_example.txt	2056	0644	edit dl rm
biostacks_example.txt	1914	0644	edit dl rm
bitesize_example.txt	3003	0644	edit dl rm
capable_example.txt	2659	0644	edit dl rm
cpuwalk_example.txt	4919	0644	edit dl rm
dcsnoop_example.txt	4612	0644	edit dl rm
execsnoop_example.txt	1535	0644	edit dl rm
gethostlatency_example.txt	923	0644	edit dl rm
killsnoop_example.txt	846	0644	edit dl rm
loads_example.txt	864	0644	edit dl rm
mdflush_example.txt	1866	0644	edit dl rm
naptime_example.txt	844	0644	edit dl rm
oomkill_example.txt	1668	0644	edit dl rm
opensnoop_example.txt	2528	0644	edit dl rm
pidpersec_example.txt	1504	0644	edit dl rm
runqlat_example.txt	8632	0644	edit dl rm
runqlen_example.txt	980	0644	edit dl rm
setuids_example.txt	2441	0644	edit dl rm
ssllatency_example.txt	4510	0644	edit dl rm
sslsnoop_example.txt	1916	0644	edit dl rm
statsnoop_example.txt	2738	0644	edit dl rm
swapin_example.txt	549	0644	edit dl rm
syncsnoop_example.txt	541	0644	edit dl rm
syscount_example.txt	1144	0644	edit dl rm
tcpaccept_example.txt	1350	0644	edit dl rm
tcpconnect_example.txt	1085	0644	edit dl rm
tcpdrop_example.txt	1256	0644	edit dl rm
tcplife_example.txt	1597	0644	edit dl rm
tcpretrans_example.txt	1153	0644	edit dl rm
tcpsynbl_example.txt	940	0644	edit dl rm
threadsnoop_example.txt	1182	0644	edit dl rm
undump_example.txt	680	0644	edit dl rm
vfscount_example.txt	1199	0644	edit dl rm
vfsstat_example.txt	929	0644	edit dl rm
writeback_example.txt	1962	0644	edit dl rm
xfsdist_example.txt	3419	0644	edit dl rm

Edit: /usr/share/doc/bpftrace/examples/runqlat_example.txt (8632B)

Demonstrations of runqlat, the Linux BPF/bpftrace version.

This traces time spent waiting in the CPU scheduler for a turn on-CPU. This
metric is often called run queue latency, or scheduler latency. This tool shows
this latency as a power-of-2 histogram in nanoseconds. For example:

# ./runqlat.bt
Attaching 5 probes...
Tracing CPU scheduler... Hit Ctrl-C to end.
^C

@usecs:
[0]                    1 |                                                    |
[1]                   11 |@@                                                  |
[2, 4)                16 |@@@                                                 |
[4, 8)                43 |@@@@@@@@@@                                          |
[8, 16)              134 |@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@                     |
[16, 32)             220 |@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@|
[32, 64)             117 |@@@@@@@@@@@@@@@@@@@@@@@@@@@                         |
[64, 128)             84 |@@@@@@@@@@@@@@@@@@@                                 |
[128, 256)            10 |@@                                                  |
[256, 512)             2 |                                                    |
[512, 1K)              5 |@                                                   |
[1K, 2K)               5 |@                                                   |
[2K, 4K)               5 |@                                                   |
[4K, 8K)               4 |                                                    |
[8K, 16K)              1 |                                                    |
[16K, 32K)             2 |                                                    |
[32K, 64K)             0 |                                                    |
[64K, 128K)            1 |                                                    |
[128K, 256K)           0 |                                                    |
[256K, 512K)           0 |                                                    |
[512K, 1M)             1 |                                                    |

This is an idle system where most of the time we are waiting for less than
128 microseconds, shown by the mode above. As an example of reading the output,
the above histogram shows 220 scheduling events with a run queue latency of
between 16 and 32 microseconds.

The output also shows an outlier taking between 0.5 and 1 seconds: ??? XXX
likely work was scheduled behind another higher priority task, and had to wait
briefly. The kernel decides whether it is worth migrating such work to an
idle CPU, or leaving it wait its turn on its current CPU run queue where
the CPU caches should be hotter.

I'll now add a single-threaded CPU bound workload to this system, and bind
it on one CPU:

# ./runqlat.bt
Attaching 5 probes...
Tracing CPU scheduler... Hit Ctrl-C to end.
^C

@usecs:
[1]                    6 |@@@                                                 |
[2, 4)                26 |@@@@@@@@@@@@@                                       |
[4, 8)                97 |@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@|
[8, 16)               72 |@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@              |
[16, 32)              17 |@@@@@@@@@                                           |
[32, 64)              19 |@@@@@@@@@@                                          |
[64, 128)             20 |@@@@@@@@@@                                          |
[128, 256)             3 |@                                                   |
[256, 512)             0 |                                                    |
[512, 1K)              0 |                                                    |
[1K, 2K)               1 |                                                    |
[2K, 4K)               1 |                                                    |
[4K, 8K)               4 |@@                                                  |
[8K, 16K)              3 |@                                                   |
[16K, 32K)             0 |                                                    |
[32K, 64K)             0 |                                                    |
[64K, 128K)            0 |                                                    |
[128K, 256K)           1 |                                                    |
[256K, 512K)           0 |                                                    |
[512K, 1M)             0 |                                                    |
[1M, 2M)               1 |                                                    |

That didn't make much difference.

Now I'll add a second single-threaded CPU workload, and bind it to the same
CPU, causing contention:

# ./runqlat.bt
Attaching 5 probes...
Tracing CPU scheduler... Hit Ctrl-C to end.
^C

@usecs:
[0]                    1 |                                                    |
[1]                    8 |@@@                                                 |
[2, 4)                28 |@@@@@@@@@@@@                                        |
[4, 8)                95 |@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@           |
[8, 16)              120 |@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@|
[16, 32)              22 |@@@@@@@@@                                           |
[32, 64)              10 |@@@@                                                |
[64, 128)              7 |@@@                                                 |
[128, 256)             3 |@                                                   |
[256, 512)             1 |                                                    |
[512, 1K)              0 |                                                    |
[1K, 2K)               0 |                                                    |
[2K, 4K)               2 |                                                    |
[4K, 8K)               4 |@                                                   |
[8K, 16K)            107 |@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@      |
[16K, 32K)             0 |                                                    |
[32K, 64K)             0 |                                                    |
[64K, 128K)            0 |                                                    |
[128K, 256K)           0 |                                                    |
[256K, 512K)           1 |                                                    |

There's now a second mode between 8 and 16 milliseconds, as each thread must
wait its turn on the one CPU.

Now I'll run 10 CPU-bound threads on one CPU:

# ./runqlat.bt
Attaching 5 probes...
Tracing CPU scheduler... Hit Ctrl-C to end.
^C

@usecs:
[0]                    2 |                                                    |
[1]                   10 |@                                                   |
[2, 4)                38 |@@@@                                                |
[4, 8)                63 |@@@@@@                                              |
[8, 16)              106 |@@@@@@@@@@@                                         |
[16, 32)              28 |@@@                                                 |
[32, 64)              13 |@                                                   |
[64, 128)             15 |@                                                   |
[128, 256)             2 |                                                    |
[256, 512)             2 |                                                    |
[512, 1K)              1 |                                                    |
[1K, 2K)               1 |                                                    |
[2K, 4K)               2 |                                                    |
[4K, 8K)               4 |                                                    |
[8K, 16K)              3 |                                                    |
[16K, 32K)             0 |                                                    |
[32K, 64K)           478 |@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@|
[64K, 128K)            1 |                                                    |
[128K, 256K)           0 |                                                    |
[256K, 512K)           0 |                                                    |
[512K, 1M)             0 |                                                    |
[1M, 2M)               1 |                                                    |

This shows that most of the time threads need to wait their turn, with the
largest mode between 32 and 64 milliseconds.

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

cmd: