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tracing/timerlat: Notify IRQ new max latency only if stop tracing is set

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Currently, the notification of a new max latency is sent from
timerlat's IRQ handler anytime a new max latency is found.

While this behavior is not wrong, the send IPI overhead itself
will increase the thread latency and that is not the desired
effect (tracing overhead).

Moreover, the thread will notify a new max latency again because
the thread latency as it is always higher than the IRQ latency
that woke it up.

The only case in which it is helpful to notify a new max latency
from IRQ is when stop tracing (for the IRQ) is set, as in this
case, the thread will not be dispatched.

Notify a new max latency from the IRQ handler only if stop tracing is
set for the IRQ handler.

Link: https://lkml.kernel.org/r/2c2d9a56c0886c8402ba320de32856cbbb10c2bb.1652175637.git.bristot@kernel.org

Cc: Juri Lelli <juri.lelli@redhat.com>
Cc: Ingo Molnar <mingo@redhat.com>
Reported-by: Clark Williams <williams@redhat.com>
Fixes: a955d7eac1 ("trace: Add timerlat tracer")
Signed-off-by: Daniel Bristot de Oliveira <bristot@kernel.org>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
This commit is contained in:
Daniel Bristot de Oliveira 2022-05-10 11:45:23 +02:00 committed by Steven Rostedt (Google)
parent 4399404918
commit aa748949b4
1 changed files with 5 additions and 4 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

9
kernel/trace/trace_osnoise.c
View File

@ -1578,11 +1578,12 @@ static enum hrtimer_restart timerlat_irq(struct hrtimer *timer)
trace_timerlat_sample(&s);
notify_new_max_latency(diff);
if (osnoise_data.stop_tracing)
if (time_to_us(diff) >= osnoise_data.stop_tracing)
if (osnoise_data.stop_tracing) {
if (time_to_us(diff) >= osnoise_data.stop_tracing) {
osnoise_stop_tracing();
notify_new_max_latency(diff);
}
}
wake_up_process(tlat->kthread);