From: Daniel Bristot de Oliveira bristot@kernel.org
[ Upstream commit aa748949b4e665f473bc5abdc5f66029cb5f5522 ]
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.165217563...
Cc: Juri Lelli juri.lelli@redhat.com Cc: Ingo Molnar mingo@redhat.com Reported-by: Clark Williams williams@redhat.com Fixes: a955d7eac177 ("trace: Add timerlat tracer") Signed-off-by: Daniel Bristot de Oliveira bristot@kernel.org Signed-off-by: Steven Rostedt (Google) rostedt@goodmis.org Signed-off-by: Sasha Levin sashal@kernel.org --- kernel/trace/trace_osnoise.c | 9 +++++---- 1 file changed, 5 insertions(+), 4 deletions(-)
diff --git a/kernel/trace/trace_osnoise.c b/kernel/trace/trace_osnoise.c index 5e3c62a08fc0..61c3fff488bf 100644 --- a/kernel/trace/trace_osnoise.c +++ b/kernel/trace/trace_osnoise.c @@ -1576,11 +1576,12 @@ 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);