rtla-timerlat-hist - Man Page

Histograms of the operating system timer latency

Synopsis

rtla timerlat hist [Options] ...

Description

The rtla timerlat tool is an interface for the timerlat tracer. The timerlat tracer dispatches a kernel thread per-cpu. These threads set a periodic timer to wake themselves up and go back to sleep. After the wakeup, they collect and generate useful information for the debugging of operating system timer latency.

The timerlat tracer outputs information in two ways. It periodically prints the timer latency at the timer IRQ handler and the Thread handler. It also enable the trace of the most relevant information via osnoise: tracepoints.

The rtla timerlat hist displays a histogram of each tracer event occurrence. This tool uses the periodic information, and the osnoise: tracepoints are enabled when using the -T option.

Options

-a,  --auto us

Set the automatic trace mode. This mode sets some commonly used options while debugging the system. It is equivalent to use -T us -s us -t. By default, timerlat tracer uses FIFO:95 for timerlat threads, thus equilavent to -P f:95.

-p,  --period us

Set the timerlat tracer period in microseconds.

-i,  --irq us

Stop trace if the IRQ latency is higher than the argument in us.

-T,  --thread us

Stop trace if the Thread latency is higher than the argument in us.

-s,  --stack us

Save the stack trace at the IRQ if a Thread latency is higher than the argument in us.

--dma-latency us

Set the /dev/cpu_dma_latency to us, aiming to bound exit from idle latencies. cyclictest sets this value to 0 by default, use --dma-latency 0 to have similar results.

-u,  --user-threads

Set timerlat to run without a workload, and then dispatches user-space workloads to wait on the timerlat_fd. Once the workload is awakes, it goes to sleep again adding so the measurement for the kernel-to-user and user-to-kernel to the tracer output.

-b,  --bucket-size N

Set the histogram bucket size (default 1).

-E,  --entries N

Set the number of entries of the histogram (default 256).

--no-header

Do not print header.

--no-summary

Do not print summary.

--no-index

Do not print index.

--with-zeros

Print zero only entries.

-c,  --cpus cpu-list

Set the osnoise tracer to run the sample threads in the cpu-list.

-H,  --house-keeping cpu-list

Run rtla control threads only on the given cpu-list.

-d,  --duration time[s|m|h|d]

Set the duration of the session.

-D,  --debug

Print debug info.

-t,  --trace[=file]

Save the stopped trace to [file|osnoise_trace.txt].

-e,  --event sys:event

Enable an event in the trace (-t) session. The argument can be a specific event, e.g., -e sched:sched_switch, or all events of a system group, e.g., -e sched. Multiple -e are allowed. It is only active when -t or -a are set.

--filter <filter>

Filter the previous -e sys:event event with <filter>. For further information about event filtering see https://www.kernel.org/doc/html/latest/trace/events.html#event-filtering.

--trigger <trigger>

Enable a trace event trigger to the previous -e sys:event. If the hist: trigger is activated, the output histogram will be automatically saved to a file named system_event_hist.txt. For example, the command:

rtla <command> <mode> -t -e osnoise:irq_noise --trigger="hist:key=desc,duration/1000:sort=desc,duration/1000:vals=hitcount"

Will automatically save the content of the histogram associated to osnoise:irq_noise event in osnoise_irq_noise_hist.txt.

For further information about event trigger see https://www.kernel.org/doc/html/latest/trace/events.html#event-triggers.

-P,  --priority o:prio|r:prio|f:prio|d:runtime:period

Set scheduling parameters to the osnoise tracer threads, the format to set the priority are:

  • o:prio - use SCHED_OTHER with prio;
  • r:prio - use SCHED_RR with prio;
  • f:prio - use SCHED_FIFO with prio;
  • d:runtime[us|ms|s]:period[us|ms|s] - use SCHED_DEADLINE with runtime and period in nanoseconds.
-C,  --cgroup[=cgroup]

Set a cgroup to the tracer's threads. If the -C option is passed without arguments, the tracer's thread will inherit rtla's cgroup. Otherwise, the threads will be placed on the cgroup passed to the option.

-h,  --help

Print help menu.

--dump-tasks

prints the task running on all CPUs if stop conditions are met (depends on !--no-aa)

--no-aa

disable auto-analysis, reducing rtla timerlat cpu usage

Example

In the example below, rtla timerlat hist is set to run for 10 minutes, in the cpus 0-4, skipping zero only lines. Moreover, rtla timerlat hist will change the priority of the timerlat threads to run under SCHED_DEADLINE priority, with a 100us runtime every 1ms period. The 1ms period is also passed to the timerlat tracer. Auto-analysis is disabled to reduce overhead

[root@alien ~]# timerlat hist -d 10m -c 0-4 -P d:100us:1ms -p 1000 --no-aa
# RTLA timerlat histogram
# Time unit is microseconds (us)
# Duration:   0 00:10:00
Index   IRQ-000   Thr-000   IRQ-001   Thr-001   IRQ-002   Thr-002   IRQ-003   Thr-003   IRQ-004   Thr-004
0        276489         0    206089         0    466018         0    481102         0    205546         0
1        318327     35487    388149     30024     94531     48382     83082     71078    388026     55730
2          3282    122584      4019    126527     28231    109012     23311     89309      4568     98739
3           940     11815       837      9863      6209     16227      6895     17196       910      9780
4           444     17287       424     11574      2097     38443      2169     36736       462     13476
5           206     43291       255     25581      1223    101908      1304    101137       236     28913
6           132    101501        96     64584       635    213774       757    215471        99     73453
7            74    169347        65    124758       350     57466       441     53639        69    148573
8            53     85183        31    156751       229      9052       306      9026        39    139907
9            22     10387        12     42762       161      2554       225      2689        19     26192
10           13      1898         8      5770       114      1247       128      1405        13      3772
11            9       560         9       924        71       686        76       765         8       713
12            4       256         2       360        50       411        64       474         3       278
13            2       167         2       172        43       256        53       350         4       180
14            1        88         1       116        15       198        42       223         0       115
15            2        63         3        94        11       139        20       150         0        58
16            2        37         0        56         5        78        10       102         0        39
17            0        18         0        28         4        57         8        80         0        15
18            0         8         0        17         2        50         6        56         0        12
19            0         9         0         5         0        19         0        48         0        18
20            0         4         0         8         0        11         2        27         0         4
21            0         2         0         3         1         9         1        18         0         6
22            0         1         0         3         1         7         0         3         0         5
23            0         2         0         4         0         2         0         7         0         2
24            0         2         0         2         1         3         0         3         0         5
25            0         0         0         1         0         1         0         1         0         3
26            0         1         0         0         0         2         0         2         0         0
27            0         0         0         3         0         1         0         0         0         1
28            0         0         0         3         0         0         0         1         0         0
29            0         0         0         2         0         2         0         1         0         3
30            0         1         0         0         0         0         0         0         0         0
31            0         1         0         0         0         0         0         2         0         2
32            0         0         0         1         0         2         0         0         0         0
33            0         0         0         2         0         0         0         0         0         1
34            0         0         0         0         0         0         0         0         0         2
35            0         1         0         1         0         0         0         0         0         1
36            0         1         0         0         0         1         0         1         0         0
37            0         0         0         1         0         0         0         0         0         0
40            0         0         0         0         0         1         0         1         0         0
41            0         0         0         0         0         0         0         0         0         1
42            0         0         0         0         0         0         0         0         0         1
44            0         0         0         0         0         1         0         0         0         0
46            0         0         0         0         0         0         0         1         0         0
47            0         0         0         0         0         0         0         0         0         1
50            0         0         0         0         0         0         0         0         0         1
54            0         0         0         1         0         0         0         0         0         0
58            0         0         0         1         0         0         0         0         0         0
over:         0         0         0         0         0         0         0         0         0         0
count:   600002    600002    600002    600002    600002    600002    600002    600002    600002    600002
min:          0         1         0         1         0         1         0         1         0         1
avg:          0         5         0         5         0         4         0         4         0         5
max:         16        36        15        58        24        44        21        46        13        50

See Also

rtla-timerlat(1), rtla-timerlat-top(1)

timerlat tracer documentation: <https://www.kernel.org/doc/html/latest/trace/timerlat-tracer.html>

Author

Written by Daniel Bristot de Oliveira <bristot@kernel.org>

Referenced By

rtla-timerlat(1), rtla-timerlat-top(1).