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tracing/doc: Fix typos on the timerlat tracer documentation

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Fixes a series of typos in the timerlat doc.

Link: https://lkml.kernel.org/r/d3763eb376603890baab908141de6660ba18fff8.1634308385.git.bristot@kernel.org

Cc: Daniel Bristot de Oliveira <bristot@kernel.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: x86@kernel.org
Cc: linux-doc@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Fixes: a955d7eac1 ("trace: Add timerlat tracer")
Signed-off-by: Daniel Bristot de Oliveira <bristot@kernel.org>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
This commit is contained in:
Daniel Bristot de Oliveira 2021-10-15 17:07:49 +02:00 committed by Steven Rostedt (VMware)
parent 9bd985766a
commit 4d4eac7b5a
1 changed files with 12 additions and 12 deletions
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24
Documentation/trace/timerlat-tracer.rst
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@ -3,7 +3,7 @@ Timerlat tracer
############### ###############
The timerlat tracer aims to help the preemptive kernel developers to The timerlat tracer aims to help the preemptive kernel developers to
find souces of wakeup latencies of real-time threads. Like cyclictest, find sources of wakeup latencies of real-time threads. Like cyclictest,
the tracer sets a periodic timer that wakes up a thread. The thread then the tracer sets a periodic timer that wakes up a thread. The thread then
computes a *wakeup latency* value as the difference between the *current computes a *wakeup latency* value as the difference between the *current
time* and the *absolute time* that the timer was set to expire. The main time* and the *absolute time* that the timer was set to expire. The main
@ -50,14 +50,14 @@ The second is the *timer latency* observed by the thread. The ACTIVATION
ID field serves to relate the *irq* execution to its respective *thread* ID field serves to relate the *irq* execution to its respective *thread*
execution. execution.
The *irq*/*thread* splitting is important to clarify at which context The *irq*/*thread* splitting is important to clarify in which context
the unexpected high value is coming from. The *irq* context can be the unexpected high value is coming from. The *irq* context can be
delayed by hardware related actions, such as SMIs, NMIs, IRQs delayed by hardware-related actions, such as SMIs, NMIs, IRQs,
or by a thread masking interrupts. Once the timer happens, the delay or by thread masking interrupts. Once the timer happens, the delay
can also be influenced by blocking caused by threads. For example, by can also be influenced by blocking caused by threads. For example, by
postponing the scheduler execution via preempt_disable(), by the postponing the scheduler execution via preempt_disable(), scheduler
scheduler execution, or by masking interrupts. Threads can execution, or masking interrupts. Threads can also be delayed by the
also be delayed by the interference from other threads and IRQs. interference from other threads and IRQs.
Tracer options Tracer options
--------------------- ---------------------
@ -68,14 +68,14 @@ directory. The timerlat configs are:
- cpus: CPUs at which a timerlat thread will execute. - cpus: CPUs at which a timerlat thread will execute.
- timerlat_period_us: the period of the timerlat thread. - timerlat_period_us: the period of the timerlat thread.
- osnoise/stop_tracing_us: stop the system tracing if a - stop_tracing_us: stop the system tracing if a
timer latency at the *irq* context higher than the configured timer latency at the *irq* context higher than the configured
value happens. Writing 0 disables this option. value happens. Writing 0 disables this option.
- stop_tracing_total_us: stop the system tracing if a - stop_tracing_total_us: stop the system tracing if a
timer latency at the *thread* context higher than the configured timer latency at the *thread* context is higher than the configured
value happens. Writing 0 disables this option. value happens. Writing 0 disables this option.
- print_stack: save the stack of the IRQ ocurrence, and print - print_stack: save the stack of the IRQ occurrence, and print
it afte the *thread context* event". it after the *thread context* event".
timerlat and osnoise timerlat and osnoise
---------------------------- ----------------------------
@ -95,7 +95,7 @@ For example::
timerlat/5-1035 [005] ....... 548.771104: #402268 context thread timer_latency 39960 ns timerlat/5-1035 [005] ....... 548.771104: #402268 context thread timer_latency 39960 ns
In this case, the root cause of the timer latency does not point to a In this case, the root cause of the timer latency does not point to a
single cause, but to multiple ones. Firstly, the timer IRQ was delayed single cause but to multiple ones. Firstly, the timer IRQ was delayed
for 13 us, which may point to a long IRQ disabled section (see IRQ for 13 us, which may point to a long IRQ disabled section (see IRQ
stacktrace section). Then the timer interrupt that wakes up the timerlat stacktrace section). Then the timer interrupt that wakes up the timerlat
thread took 7597 ns, and the qxl:21 device IRQ took 7139 ns. Finally, thread took 7597 ns, and the qxl:21 device IRQ took 7139 ns. Finally,