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.
- -t, --trace [file]
Save the stopped trace to [file|timerlat_trace.txt].
- --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.
- -k, --kernel-threads
Use timerlat kernel-space threads, in contrast of -u.
- -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. --user-threads will be used unless the user specify -k.
- -U, --user-load
Set timerlat to run without workload, waiting for the user to dispatch a per-cpu task that waits for a new period on the tracing/osnoise/per_cpu/cpu$ID/timerlat_fd. See linux/tools/rtla/sample/timerlat_load.py for an example of user-load code.
- -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.
- -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.
- --warm-up s
After starting the workload, let it run for s seconds before starting collecting the data, allowing the system to warm-up. Statistical data generated during warm-up is discarded.
- --trace-buffer-size kB
Set the per-cpu trace buffer size in kB for the tracing output.
- -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> >