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path: root/tools/tracing/rtla/src/timerlat_top.c
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2024-03-20tools/rtla: Add -U/--user-load option to timerlatDaniel Bristot de Oliveira
The timerlat tracer provides an interface for any application to wait for the timerlat's periodic wakeup. Currently, rtla timerlat uses it to dispatch its user-space workload (-u option). But as the tracer interface is generic, rtla timerlat can also be used to monitor any workload that uses it. For example, a user might place their own workload to wait on the tracer interface, and monitor the results with rtla timerlat. Add the -U option to rtla timerlat top and hist. With this option, rtla timerlat will not dispatch its workload but only setting up the system, waiting for a user to dispatch its workload. The sample code in this patch is an example of python application that loops in the timerlat tracer fd. To use it, dispatch: # rtla timerlat -U In a terminal, then run the python program on another terminal, specifying the CPU to run it. For example, setting on CPU 1: #./timerlat_load.py 1 Then rtla timerlat will start printing the statistics of the ./timerlat_load.py app. An interesting point is that the "Ret user Timer Latency" value is the overall response time of the load. The sample load does a memory copy to exemplify that. The stop tracing options on rtla timerlat works in this setup as well, including auto analysis. Link: https://lkml.kernel.org/r/36e6bcf18fe15c7601048fd4c65aeb193c502cc8.1707229706.git.bristot@kernel.org Cc: Jonathan Corbet <corbet@lwn.net> Cc: Masami Hiramatsu <mhiramat@kernel.org> Signed-off-by: Daniel Bristot de Oliveira <bristot@kernel.org>
2024-02-12tools/rtla: Exit with EXIT_SUCCESS when help is invokedJohn Kacur
Fix rtla so that the following commands exit with 0 when help is invoked rtla osnoise top -h rtla osnoise hist -h rtla timerlat top -h rtla timerlat hist -h Link: https://lore.kernel.org/linux-trace-devel/20240203001607.69703-1-jkacur@redhat.com Cc: stable@vger.kernel.org Fixes: 1eeb6328e8b3 ("rtla/timerlat: Add timerlat hist mode") Signed-off-by: John Kacur <jkacur@redhat.com> Signed-off-by: Daniel Bristot de Oliveira <bristot@kernel.org>
2023-06-13rtla/timerlat_top: Add timerlat user-space supportDaniel Bristot de Oliveira
Add the support for running timerlat threads in user-space. In this mode, enabled with -u/--user-threads, timerlat dispatches user-space processes that will loop in the timerlat_fd, measuring the overhead for going to user-space and then returning to the kernel - in addition to the existing measurements. Here is one example of the tool's output with -u enabled: $ sudo timerlat top -u -d 600 -q Timer Latency 0 00:10:01 | IRQ Timer Latency (us) | Thread Timer Latency (us) | Ret user Timer Latency (us) CPU COUNT | cur min avg max | cur min avg max | cur min avg max 0 #600001 | 0 0 0 3 | 2 1 2 9 | 3 2 3 15 1 #600001 | 0 0 0 2 | 2 1 2 13 | 2 2 3 18 2 #600001 | 0 0 0 10 | 2 1 2 16 | 3 2 3 20 3 #600001 | 0 0 0 7 | 2 1 2 10 | 3 2 3 11 4 #600000 | 0 0 0 16 | 2 1 2 41 | 3 2 3 58 5 #600000 | 0 0 0 3 | 2 1 2 10 | 3 2 3 13 6 #600000 | 0 0 0 5 | 2 1 2 7 | 3 2 3 10 7 #600000 | 0 0 0 1 | 2 1 2 7 | 3 2 3 10 The tuning setup like -p or -C work for the user-space threads as well. Link: https://lkml.kernel.org/r/758ad2292a0a1d884138d08219e1a0f572d257a2.1686066600.git.bristot@kernel.org Cc: William White <chwhite@redhat.com> Cc: Jonathan Corbet <corbet@lwn.net> Tested-by: Juri Lelli <juri.lelli@redhat.com> Signed-off-by: Daniel Bristot de Oliveira <bristot@kernel.org> Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
2023-06-13rtla: Start the tracers after creating all instancesDaniel Bristot de Oliveira
Group all start tracing after finishing creating all instances. The tracing instance starts first for the case of hitting a stop tracing while enabling other instances. The trace instance is the one with most valuable information. Link: https://lkml.kernel.org/r/67da7a703a56f75d7cd46568525145a65501a7e8.1686066600.git.bristot@kernel.org Cc: William White <chwhite@redhat.com> Cc: Jonathan Corbet <corbet@lwn.net> Tested-by: Juri Lelli <juri.lelli@redhat.com> Signed-off-by: Daniel Bristot de Oliveira <bristot@kernel.org> Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
2023-06-13rtla/timerlat: Give timerlat auto analysis its own instanceDaniel Bristot de Oliveira
Currently, the auto-analysis is attached to the timerlat top instance. The idea was to avoid creating another instance just for that, so one instance could be reused. The drawback is that, by doing so, the auto-analysis run for the entire session, consuming CPU time. On my 24 box CPUs for timerlat with a 100 us period consumed 50 % with auto analysis, but only 16 % without. By creating an instance for auto-analysis, we can keep the processing stopped until a stop tracing condition is hit. Once it happens, timerlat auto-analysis can use its own trace instance to parse only the end of the trace. By doing so, auto-analysis stop consuming cpu time when it is not needed. If the --aa-only is passed, the timerlat top instance is reused for auto analysis. Link: https://lkml.kernel.org/r/346b7168c1bae552a415715ec6d23c129a43bdb7.1686066600.git.bristot@kernel.org Cc: William White <chwhite@redhat.com> Cc: Jonathan Corbet <corbet@lwn.net> Tested-by: Juri Lelli <juri.lelli@redhat.com> Signed-off-by: Daniel Bristot de Oliveira <bristot@kernel.org> Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
2023-06-13rtla: Automatically move rtla to a house-keeping cpuDaniel Bristot de Oliveira
When the user sets -c <cpu-list> try to move rtla out of the <cpu-list>, even without an -H option. This is useful to avoid having rtla interfering with the workload. This works by removing <cpu-list> from rtla's current affinity. If rtla fails to move itself away it is not that of a problem as this is an automatic measure. Link: https://lkml.kernel.org/r/c54304d90c777310fb85a3e658d1449173759aab.1686066600.git.bristot@kernel.org Cc: William White <chwhite@redhat.com> Cc: Jonathan Corbet <corbet@lwn.net> Tested-by: Juri Lelli <juri.lelli@redhat.com> Signed-off-by: Daniel Bristot de Oliveira <bristot@kernel.org> Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
2023-06-13rtla: Change monitored_cpus from char * to cpu_set_tDaniel Bristot de Oliveira
Use a cpumask instead of a char *, reducing memory footprint and code. No functional change, and in preparation for auto house-keeping. Link: https://lkml.kernel.org/r/54c46293261d13cb1042d0314486539eeb45fe5d.1686066600.git.bristot@kernel.org Cc: William White <chwhite@redhat.com> Cc: Jonathan Corbet <corbet@lwn.net> Tested-by: Juri Lelli <juri.lelli@redhat.com> Signed-off-by: Daniel Bristot de Oliveira <bristot@kernel.org> Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
2023-06-13rtla: Add --house-keeping optionDaniel Bristot de Oliveira
To avoid having rtla interfering with the measurement threads, add an option for the user to set the CPUs in which rtla should run. For instance: # rtla timerlat top -H 0 -c 1-7 Will place rtla in the CPU 0, while running the measurement threads in the CPU 1-7. Link: https://lkml.kernel.org/r/6a6c78a579a96ba8b02ae67ee1e0ba2cb5e03c4a.1686066600.git.bristot@kernel.org Cc: William White <chwhite@redhat.com> Cc: Jonathan Corbet <corbet@lwn.net> Tested-by: Juri Lelli <juri.lelli@redhat.com> Suggested-by: Juri Lelli <juri.lelli@redhat.com> Signed-off-by: Daniel Bristot de Oliveira <bristot@kernel.org> Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
2023-06-13rtla: Add -C cgroup supportDaniel Bristot de Oliveira
The -C option sets 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. Link: https://lkml.kernel.org/r/cb051477331d292f17c08bf1d66f0e0384bbe5a5.1686066600.git.bristot@kernel.org Cc: William White <chwhite@redhat.com> Cc: Jonathan Corbet <corbet@lwn.net> Tested-by: Juri Lelli <juri.lelli@redhat.com> Signed-off-by: Daniel Bristot de Oliveira <bristot@kernel.org> Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
2023-04-25rtla/timerlat: Add auto-analysis only optionDaniel Bristot de Oliveira
Parsing and formating timerlat data might consume a reasonable amount of CPU time on very large systems, or when timerlat has a too short period. Add an option to run timerlat with auto-analysis enabled while skipping the statistics parsing. In this mode, rtla timerlat periodically checks if the tracing is on, going to sleep waiting for the stop tracing condition to stop tracing, or for the tracing session to finish. If the stop tracing condition is hit, the tool prints the auto analysis. Otherwise, the tool prints the max observed latency and exit. The max observed latency is captured via tracing_max_latency. Link: https://lore.kernel.org/linux-trace-devel/4dc514d1d5dc353c537a466a9b5af44c266b6da2.1680106912.git.bristot@kernel.org Cc: Jonathan Corbet <corbet@lwn.net> Signed-off-by: Daniel Bristot de Oliveira <bristot@kernel.org> Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
2023-02-02rtla/timerlat: Add auto-analysis support to timerlat topDaniel Bristot de Oliveira
Currently, timerlat top displays the timerlat tracer latency results, saving the intuitive timerlat trace for the developer to analyze. This patch goes a step forward in the automaton of the scheduling latency analysis by providing a summary of the root cause of a latency higher than the passed "stop tracing" parameter if the trace stops. The output is intuitive enough for non-expert users to have a general idea of the root cause by looking at each factor's contribution percentage while keeping the technical detail in the output for more expert users to start an in dept debug or to correlate a root cause with an existing one. The terminology is in line with recent industry and academic publications to facilitate the understanding of both audiences. Here is one example of tool output: ----------------------------------------- %< ----------------------------------------------------- # taskset -c 0 timerlat -a 40 -c 1-23 -q Timer Latency 0 00:00:12 | IRQ Timer Latency (us) | Thread Timer Latency (us) CPU COUNT | cur min avg max | cur min avg max 1 #12322 | 0 0 1 15 | 10 3 9 31 2 #12322 | 3 0 1 12 | 10 3 9 23 3 #12322 | 1 0 1 21 | 8 2 8 34 4 #12322 | 1 0 1 17 | 10 2 11 33 5 #12322 | 0 0 1 12 | 8 3 8 25 6 #12322 | 1 0 1 14 | 16 3 11 35 7 #12322 | 0 0 1 14 | 9 2 8 29 8 #12322 | 1 0 1 22 | 9 3 9 34 9 #12322 | 0 0 1 14 | 8 2 8 24 10 #12322 | 1 0 0 12 | 9 3 8 24 11 #12322 | 0 0 0 15 | 6 2 7 29 12 #12321 | 1 0 0 13 | 5 3 8 23 13 #12319 | 0 0 1 14 | 9 3 9 26 14 #12321 | 1 0 0 13 | 6 2 8 24 15 #12321 | 1 0 1 15 | 12 3 11 27 16 #12318 | 0 0 1 13 | 7 3 10 24 17 #12319 | 0 0 1 13 | 11 3 9 25 18 #12318 | 0 0 0 12 | 8 2 8 20 19 #12319 | 0 0 1 18 | 10 2 9 28 20 #12317 | 0 0 0 20 | 9 3 8 34 21 #12318 | 0 0 0 13 | 8 3 8 28 22 #12319 | 0 0 1 11 | 8 3 10 22 23 #12320 | 28 0 1 28 | 41 3 11 41 rtla timerlat hit stop tracing ## CPU 23 hit stop tracing, analyzing it ## IRQ handler delay: 27.49 us (65.52 %) IRQ latency: 28.13 us Timerlat IRQ duration: 9.59 us (22.85 %) Blocking thread: 3.79 us (9.03 %) objtool:49256 3.79 us Blocking thread stacktrace -> timerlat_irq -> __hrtimer_run_queues -> hrtimer_interrupt -> __sysvec_apic_timer_interrupt -> sysvec_apic_timer_interrupt -> asm_sysvec_apic_timer_interrupt -> _raw_spin_unlock_irqrestore -> cgroup_rstat_flush_locked -> cgroup_rstat_flush_irqsafe -> mem_cgroup_flush_stats -> mem_cgroup_wb_stats -> balance_dirty_pages -> balance_dirty_pages_ratelimited_flags -> btrfs_buffered_write -> btrfs_do_write_iter -> vfs_write -> __x64_sys_pwrite64 -> do_syscall_64 -> entry_SYSCALL_64_after_hwframe ------------------------------------------------------------------------ Thread latency: 41.96 us (100%) The system has exit from idle latency! Max timerlat IRQ latency from idle: 17.48 us in cpu 4 Saving trace to timerlat_trace.txt ----------------------------------------- >% ----------------------------------------------------- In this case, the major factor was the delay suffered by the IRQ handler that handles timerlat wakeup: 65.52 %. This can be caused by the current thread masking interrupts, which can be seen in the blocking thread stacktrace: the current thread (objtool:49256) disabled interrupts via raw spin lock operations inside mem cgroup, while doing write syscall in a btrfs file system. A simple search for the function name on Google shows that this is a legit case for disabling the interrupts: cgroup: Use irqsave in cgroup_rstat_flush_locked() lore.kernel.org/linux-mm/20220301122143.1521823-2-bigeasy@linutronix.de/ The output also prints other reasons for the latency root cause, such as: - an IRQ that happened before the IRQ handler that caused delays - The interference from NMI, IRQ, Softirq, and Threads The details about how these factors affect the scheduling latency can be found here: https://bristot.me/demystifying-the-real-time-linux-latency/ Link: https://lkml.kernel.org/r/3d45f40e630317f51ac6d678e2d96d310e495729.1675179318.git.bristot@kernel.org Cc: Daniel Bristot de Oliveira <bristot@kernel.org> Cc: Jonathan Corbet <corbet@lwn.net> Signed-off-by: Daniel Bristot de Oliveira <bristot@kernel.org> Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
2022-08-10rtla: Fix tracer nameAlexandre Vicenzi
The correct tracer name is timerlat and not timelat. Link: https://lore.kernel.org/linux-trace-devel/20220808180343.22262-1-alexandre.vicenzi@suse.com Signed-off-by: Alexandre Vicenzi <alexandre.vicenzi@suse.com> Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
2022-05-26rtla: Avoid record NULL pointer dereferenceWan Jiabing
Fix the following null/deref_null.cocci errors: ./tools/tracing/rtla/src/osnoise_hist.c:870:31-36: ERROR: record is NULL but dereferenced. ./tools/tracing/rtla/src/osnoise_top.c:650:31-36: ERROR: record is NULL but dereferenced. ./tools/tracing/rtla/src/timerlat_hist.c:905:31-36: ERROR: record is NULL but dereferenced. ./tools/tracing/rtla/src/timerlat_top.c:700:31-36: ERROR: record is NULL but dereferenced. "record" is NULL before calling osnoise_init_trace_tool. Add a tag "out_free" to avoid dereferring a NULL pointer. Link: https://lkml.kernel.org/r/ae0e4500d383db0884eb2820286afe34ca303778.1651247710.git.bristot@kernel.org Link: https://lore.kernel.org/r/20220408151406.34823-1-wanjiabing@vivo.com/ Cc: kael_w@yeah.net Cc: Daniel Bristot de Oliveira <bristot@kernel.org> Fixes: 51d64c3a1819 ("rtla: Add -e/--event support") Acked-by: Daniel Bristot de Oliveira <bristot@kernel.org> Signed-off-by: Wan Jiabing <wanjiabing@vivo.com> Signed-off-by: Daniel Bristot de Oliveira <bristot@kernel.org> Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
2022-03-15rtla: Tools main loop cleanupDaniel Bristot de Oliveira
I probably started using "do {} while();", but changed all but osnoise_top to "while(){};" leaving the ; behind. Cleanup the main loop code, making all tools use "while() {}" Changcheng Deng reported this problem, as reported by coccicheck: Fix the following coccicheck review: ./tools/tracing/rtla/src/timerlat_hist.c: 800: 2-3: Unneeded semicolon ./tools/tracing/rtla/src/osnoise_hist.c: 776: 2-3: Unneeded semicolon ./tools/tracing/rtla/src/timerlat_top.c: 596: 2-3: Unneeded semicolon Link: https://lkml.kernel.org/r/3c1642110aa87c396f5da4a037dabc72dbb9c601.1646247211.git.bristot@kernel.org Cc: Daniel Bristot de Oliveira <bristot@kernel.org> Cc: Clark Williams <williams@redhat.com> Cc: Juri Lelli <juri.lelli@redhat.com> Cc: Jonathan Corbet <corbet@lwn.net> Reported-by: Changcheng Deng <deng.changcheng@zte.com.cn> Reported-by: Zeal Robot <zealci@zte.com.cn> Signed-off-by: Daniel Bristot de Oliveira <bristot@kernel.org> Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
2022-03-15rtla/timerlat: Add --dma-latency optionDaniel Bristot de Oliveira
Add the --dma-latency to set /dev/cpu_dma_latency to the specified value, this aims to avoid having exit from idle states latencies that could be influencing the analysis. Link: https://lkml.kernel.org/r/72ddb0d913459f13217086dadafad88a7c46dd28.1646247211.git.bristot@kernel.org Cc: Daniel Bristot de Oliveira <bristot@kernel.org> Cc: Clark Williams <williams@redhat.com> Cc: Juri Lelli <juri.lelli@redhat.com> Cc: Jonathan Corbet <corbet@lwn.net> Signed-off-by: Daniel Bristot de Oliveira <bristot@kernel.org> Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
2022-03-15rtla: Check for trace off also in the trace instanceDaniel Bristot de Oliveira
With the addition of --trigger option, it is also possible to stop the trace from the -t tracing instance using the traceoff trigger. Make rtla tools to check if the trace is stopped also in the trace instance, stopping the execution of the tool. Link: https://lkml.kernel.org/r/59fc7c6f23dddd5c8b7ef1782cf3da51ea2ce0f5.1646247211.git.bristot@kernel.org Cc: Daniel Bristot de Oliveira <bristot@kernel.org> Cc: Clark Williams <williams@redhat.com> Cc: Juri Lelli <juri.lelli@redhat.com> Cc: Jonathan Corbet <corbet@lwn.net> Signed-off-by: Daniel Bristot de Oliveira <bristot@kernel.org> Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
2022-03-15rtla: Add --filter supportDaniel Bristot de Oliveira
Add --filter option. This option enables a trace event filtering of the previous -e sys:event argument. This option is available for all current tools. Link: https://lkml.kernel.org/r/509d70b6348d3e5bcbf1f07ab725ce08d063149a.1646247211.git.bristot@kernel.org Cc: Daniel Bristot de Oliveira <bristot@kernel.org> Cc: Clark Williams <williams@redhat.com> Cc: Juri Lelli <juri.lelli@redhat.com> Cc: Jonathan Corbet <corbet@lwn.net> Signed-off-by: Daniel Bristot de Oliveira <bristot@kernel.org> Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
2022-03-15rtla: Add --trigger supportDaniel Bristot de Oliveira
Add --trigger option. This option enables a trace event trigger to the previous -e sys:event argument, allowing some advanced tracing options. For instance, in a system with CPUs 2:23 isolated, it is possible to get a stack trace of thread wakeup targeting those CPUs while running osnoise with the following command line: # osnoise top -c 2-23 -a 50 -e sched:sched_wakeup --trigger="stacktrace if target_cpu >= 2" This option is available for all current tools. Link: https://lkml.kernel.org/r/07d2983d5f71261d4da89dbaf02efcad100ab8ee.1646247211.git.bristot@kernel.org Cc: Daniel Bristot de Oliveira <bristot@kernel.org> Cc: Clark Williams <williams@redhat.com> Cc: Juri Lelli <juri.lelli@redhat.com> Cc: Jonathan Corbet <corbet@lwn.net> Signed-off-by: Daniel Bristot de Oliveira <bristot@kernel.org> Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
2022-03-15rtla: Add -e/--event supportDaniel Bristot de Oliveira
Add -e/--event option. This option enables 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. This option is available for all current tools. Link: https://lkml.kernel.org/r/6a3b753be9b1e811953995f7f21a86918ad13390.1646247211.git.bristot@kernel.org Cc: Daniel Bristot de Oliveira <bristot@kernel.org> Cc: Clark Williams <williams@redhat.com> Cc: Juri Lelli <juri.lelli@redhat.com> Cc: Jonathan Corbet <corbet@lwn.net> Signed-off-by: Daniel Bristot de Oliveira <bristot@kernel.org> Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
2022-03-15rtla/timerlat: Add the automatic trace optionDaniel Bristot de Oliveira
Add the -a/--auto <arg in us> option. This option sets some commonly used options while debugging the system. It aims to help users produce reports in the field, reducing the number of arguments passed to the tool in the first approach to a problem. It is equivalent to setting osnoise/stop_tracing_total_us and print_stack with the argument, and saving the trace to timerlat_trace.txt file if the trace is stopped automatically. Link: https://lkml.kernel.org/r/92438f7ef132c731f538cebdf77850300afe04a5.1646247211.git.bristot@kernel.org Cc: Daniel Bristot de Oliveira <bristot@kernel.org> Cc: Clark Williams <williams@redhat.com> Cc: Juri Lelli <juri.lelli@redhat.com> Cc: Jonathan Corbet <corbet@lwn.net> Signed-off-by: Daniel Bristot de Oliveira <bristot@kernel.org> Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
2022-02-08rtla: Fix segmentation fault when failing to enable -tDaniel Bristot de Oliveira
rtla osnoise and timerlat are causing a segmentation fault when running with the --trace option on a kernel that does not support multiple instances. For example: [root@f34 rtla]# rtla osnoise top -t failed to enable the tracer osnoise Could not enable osnoiser tracer for tracing Failed to enable the trace instance Segmentation fault (core dumped) This error happens because the exit code of the tools is trying to destroy the trace instance that failed to be created. Make osnoise_destroy_tool() aware of possible NULL osnoise_tool *, and do not attempt to destroy it. This also simplifies the exit code. Link: https://lkml.kernel.org/r/5660a2b6bf66c2655842360f2d7f6b48db5dba23.1644327249.git.bristot@kernel.org Suggested-by: Steven Rostedt <rostedt@goodmis.org> Fixes: 1eceb2fc2ca5 ("rtla/osnoise: Add osnoise top mode") Fixes: 829a6c0b5698 ("rtla/osnoise: Add the hist mode") Fixes: a828cd18bc4a ("rtla: Add timerlat tool and timelart top mode") Fixes: 1eeb6328e8b3 ("rtla/timerlat: Add timerlat hist mode") Signed-off-by: Daniel Bristot de Oliveira <bristot@kernel.org> Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
2022-01-13rtla: Add timerlat tool and timelart top modeDaniel Bristot de Oliveira
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 provides information for each noise via the osnoise tracepoints. The rtla timerlat top mode displays a summary of the periodic output from the timerlat tracer. Here is one example of the rtla timerlat tool output: ---------- %< ---------- [root@alien ~]# rtla timerlat top -c 0-3 -d 1m Timer Latency 0 00:01:00 | IRQ Timer Latency (us) | Thread Timer Latency (us) CPU COUNT | cur min avg max | cur min avg max 0 #60001 | 0 0 0 3 | 1 1 1 6 1 #60001 | 0 0 0 3 | 2 1 1 5 2 #60001 | 0 0 1 6 | 1 1 2 7 3 #60001 | 0 0 0 7 | 1 1 1 11 ---------- >% ---------- Running: # rtla timerlat --help # rtla timerlat top --help provides information about the available options. Link: https://lkml.kernel.org/r/e95032e20c2b88c962195bf7693bb53c9ebcced8.1639158831.git.bristot@kernel.org Cc: Tao Zhou <tao.zhou@linux.dev> Cc: Ingo Molnar <mingo@redhat.com> Cc: Tom Zanussi <zanussi@kernel.org> Cc: Masami Hiramatsu <mhiramat@kernel.org> Cc: Juri Lelli <juri.lelli@redhat.com> Cc: Clark Williams <williams@redhat.com> Cc: John Kacur <jkacur@redhat.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de> Cc: Daniel Bristot de Oliveira <bristot@kernel.org> Cc: linux-rt-users@vger.kernel.org Cc: linux-trace-devel@vger.kernel.org Cc: linux-kernel@vger.kernel.org Signed-off-by: Daniel Bristot de Oliveira <bristot@kernel.org> Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
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