From: Steven Rostedt <rostedt@goodmis.org>
To: Claudio <claudio.fontana@gliwa.com>
Cc: Ingo Molnar <mingo@redhat.com>,
Peter Zijlstra <peterz@infradead.org>,
Thomas Gleixner <tglx@linutronix.de>,
linux-kernel@vger.kernel.org
Subject: Re: ftrace performance (sched events): cyclictest shows 25% more latency
Date: Mon, 9 Jul 2018 11:11:34 -0400 [thread overview]
Message-ID: <20180709111134.08f57ac5@gandalf.local.home> (raw)
In-Reply-To: <cfb0a25b-7236-5866-6c33-838425da8d06@gliwa.com>
On Mon, 9 Jul 2018 16:53:52 +0200
Claudio <claudio.fontana@gliwa.com> wrote:
>
> One additional data point, based on brute force again:
>
> I applied this change, in order to understand if it was the
>
> trace_event_raw_event_* (I suppose primarily trace_event_raw_event_switch)
>
> that contained the latency "offenders":
>
> diff --git a/include/trace/trace_events.h b/include/trace/trace_events.h
> index 4ecdfe2..969467d 100644
> --- a/include/trace/trace_events.h
> +++ b/include/trace/trace_events.h
> @@ -704,6 +704,8 @@ trace_event_raw_event_##call(void *__data, proto)
> struct trace_event_raw_##call *entry; \
> int __data_size; \
> \
> + return; \
> + \
> if (trace_trigger_soft_disabled(trace_file)) \
> return; \
> \
>
>
> This reduces the latency overhead to 6% down from 25%.
>
> Maybe obvious? Wanted to share in case it helps, and will dig further.
I noticed that just disabling tracing "echo 0 > tracing_on" is very
similar. I'm now recording timings of various parts of the code. But at
most I've seen is a 12us, which should not add the overhead. So it's
triggering something else.
I'll be going on PTO next week, and there's things I must do this week,
thus I may not have much more time to look into this until I get back
from PTO (July 23rd).
-- Steve
next prev parent reply other threads:[~2018-07-09 15:11 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-07-06 6:22 ftrace performance (sched events): cyclictest shows 25% more latency Claudio
2018-07-06 21:24 ` Steven Rostedt
2018-07-06 21:39 ` Steven Rostedt
2018-07-06 22:00 ` Steven Rostedt
2018-07-09 10:06 ` Claudio
2018-07-09 14:53 ` Claudio
2018-07-09 15:11 ` Steven Rostedt [this message]
2018-07-09 15:32 ` Steven Rostedt
2018-07-24 9:58 ` ftrace global trace_pipe_raw Claudio
2018-07-24 14:23 ` Steven Rostedt
2018-07-24 14:25 ` Steven Rostedt
2018-07-24 15:30 ` Claudio
2018-12-19 11:32 ` Claudio
2018-12-19 16:37 ` Steven Rostedt
2019-01-16 8:00 ` Claudio
2019-01-16 13:47 ` Steven Rostedt
2018-07-24 9:59 ` Claudio
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