linux-kernel - Re: ftrace performance (sched events): cyclictest shows 25% more latency

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Message-ID: <20180706173922.734616de@gandalf.local.home>
Date:   Fri, 6 Jul 2018 17:39:22 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Claudio <claudio.fontana@...wa.com>
Cc:     Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        linux-kernel@...r.kernel.org
Subject: Re: ftrace performance (sched events): cyclictest shows 25% more
 latency

On Fri, 6 Jul 2018 17:24:28 -0400
Steven Rostedt <rostedt@...dmis.org> wrote:

> I'll investigate further.

Note, I enabled function tracing to trace the scheduler function:

 # trace-cmd start -p function -l schedule

And then ran cyclictest. That does not cause any noticeable increase
in latency (try it). So there is some kind of side effect with the
trace event itself, and not the recording of the event.

-- Steve