Commit b9f6a40d authored by Tomas Glozar's avatar Tomas Glozar Committed by Jonathan Corbet
Browse files

Documentation/trace: Specify exact priority for timerlat 



The timerlat tracer documentation mentions that threads are created with
real-time priority, but does not mention which priority and scheduling
class is used.

Add the information so that users do not have to look it up in
trace_osnoise.c.

Signed-off-by: default avatarTomas Glozar <tglozar@redhat.com>
Acked-by: default avatarSteven Rostedt (Google) <rostedt@goodmis.org>
Signed-off-by: default avatarJonathan Corbet <corbet@lwn.net>
Message-ID: <20251010083338.478961-9-tglozar@redhat.com>
parent 122a552b

Documentation/trace/timerlat-tracer.rst

+6 −6
Original line number Diff line number Diff line
@@ -43,12 +43,12 @@ It is possible to follow the trace by reading the trace file:: 
           <...>-868     [001] ....    54.030347: #2     context thread timer_latency      4351 ns





The tracer creates a per-cpu kernel thread with real-time priority that

prints two lines at every activation. The first is the *timer latency*

observed at the *hardirq* context before the activation of the thread.

The second is the *timer latency* observed by the thread. The ACTIVATION

ID field serves to relate the *irq* execution to its respective *thread*

execution.

The tracer creates a per-cpu kernel thread with real-time priority

SCHED_FIFO:95 that prints two lines at every activation. The first is

the *timer latency* observed at the *hardirq* context before the activation

of the thread. The second is the *timer latency* observed by the thread.

The ACTIVATION ID field serves to relate the *irq* execution to its

respective *thread* execution.



The *irq*/*thread* splitting is important to clarify in which context

the unexpected high value is coming from. The *irq* context can be