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tracing/doc: Fix typos on the timerlat tracer documentation
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>
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@ -3,7 +3,7 @@ Timerlat tracer
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###############
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The timerlat tracer aims to help the preemptive kernel developers to
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find souces of wakeup latencies of real-time threads. Like cyclictest,
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find sources of wakeup latencies of real-time threads. Like cyclictest,
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the tracer sets a periodic timer that wakes up a thread. The thread then
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computes a *wakeup latency* value as the difference between the *current
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time* and the *absolute time* that the timer was set to expire. The main
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@ -50,14 +50,14 @@ The second is the *timer latency* observed by the thread. The ACTIVATION
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ID field serves to relate the *irq* execution to its respective *thread*
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execution.
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The *irq*/*thread* splitting is important to clarify at which context
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The *irq*/*thread* splitting is important to clarify in which context
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the unexpected high value is coming from. The *irq* context can be
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delayed by hardware related actions, such as SMIs, NMIs, IRQs
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or by a thread masking interrupts. Once the timer happens, the delay
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delayed by hardware-related actions, such as SMIs, NMIs, IRQs,
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or by thread masking interrupts. Once the timer happens, the delay
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can also be influenced by blocking caused by threads. For example, by
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postponing the scheduler execution via preempt_disable(), by the
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scheduler execution, or by masking interrupts. Threads can
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also be delayed by the interference from other threads and IRQs.
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postponing the scheduler execution via preempt_disable(), scheduler
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execution, or masking interrupts. Threads can also be delayed by the
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interference from other threads and IRQs.
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Tracer options
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---------------------
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@ -68,14 +68,14 @@ directory. The timerlat configs are:
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- cpus: CPUs at which a timerlat thread will execute.
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- timerlat_period_us: the period of the timerlat thread.
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- osnoise/stop_tracing_us: stop the system tracing if a
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- stop_tracing_us: stop the system tracing if a
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timer latency at the *irq* context higher than the configured
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value happens. Writing 0 disables this option.
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- stop_tracing_total_us: stop the system tracing if a
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timer latency at the *thread* context higher than the configured
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timer latency at the *thread* context is higher than the configured
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value happens. Writing 0 disables this option.
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- print_stack: save the stack of the IRQ ocurrence, and print
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it afte the *thread context* event".
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- print_stack: save the stack of the IRQ occurrence, and print
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it after the *thread context* event".
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timerlat and osnoise
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----------------------------
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@ -95,7 +95,7 @@ For example::
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timerlat/5-1035 [005] ....... 548.771104: #402268 context thread timer_latency 39960 ns
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In this case, the root cause of the timer latency does not point to a
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single cause, but to multiple ones. Firstly, the timer IRQ was delayed
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single cause but to multiple ones. Firstly, the timer IRQ was delayed
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for 13 us, which may point to a long IRQ disabled section (see IRQ
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stacktrace section). Then the timer interrupt that wakes up the timerlat
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thread took 7597 ns, and the qxl:21 device IRQ took 7139 ns. Finally,
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