linux-kernel - Re: [PATCH 19/21] tracing: Account for preempt off in preempt

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Message-ID: <1316776749.29966.156.camel@gandalf.stny.rr.com>
Date:	Fri, 23 Sep 2011 07:19:09 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...e.hu>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH 19/21] tracing: Account for preempt off in
 preempt_schedule()

On Fri, 2011-09-23 at 13:00 +0200, Peter Zijlstra wrote:
>  
> > Signed-off-by: Steven Rostedt <rostedt@...dmis.org>
> > ---
> >  kernel/sched.c |    9 +++++++++
> >  1 files changed, 9 insertions(+), 0 deletions(-)
> > 
> > diff --git a/kernel/sched.c b/kernel/sched.c
> > index ccacdbd..4b096cc 100644
> > --- a/kernel/sched.c
> > +++ b/kernel/sched.c
> > @@ -4435,7 +4435,16 @@ asmlinkage void __sched notrace preempt_schedule(void)
> >  
> >  	do {
> >  		add_preempt_count_notrace(PREEMPT_ACTIVE);
> > +		/*
> > +		 * The add/subtract must not be traced by the function
> > +		 * tracer. But we still want to account for the
> > +		 * preempt off latency tracer. Since the _notrace versions
> > +		 * of add/subtract skip the accounting for latency tracer
> > +		 * we must force it manually.
> > +		 */
> > +		start_critical_timings();
> >  		schedule();
> > +		stop_critical_timings();
> >  		sub_preempt_count_notrace(PREEMPT_ACTIVE);
> >  
> >  		/*
> 
> This won't apply, you're patching ancient code.

Yes, that's the way git usually works. I could start a new branch for
this. But since we are not doing many pulls while kernel.org is down, my
kernel base has become a bit out of date. I thought that's the way Linus
wants it. I'm sure this would apply with a trivial merge fixup.

But if you want to take this patch, then I could rebase my tree and take
it out.

> 
> Anyway, this all stinks, and reading the changelog of
> d1f74e20b5b064a130cd0743a256c2d3cfe84010 and the above just makes me
> confused.
> 

What would you suggest? Just ignore the latencies that schedule
produces, even though its been one of the top causes of latencies?

-- Steve


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