linux-kernel - Re: [PATCH] Trace idle entry and exit times

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Date:	Sat, 07 Dec 2013 09:22:24 +0100
From:	Mike Galbraith <bitbucket@...ine.de>
To:	Andi Kleen <andi@...stfloor.org>
Cc:	linux-kernel@...r.kernel.org, x86@...nel.org,
	Andi Kleen <ak@...ux.intel.com>, lenb@...nel.org,
	tglx@...utronix.de, peterz@...radead.org
Subject: Re: [PATCH] Trace idle entry and exit times

On Sat, 2013-12-07 at 06:20 +0100, Andi Kleen wrote: 
> On Sat, Dec 07, 2013 at 05:57:32AM +0100, Mike Galbraith wrote:
> > On Fri, 2013-12-06 at 16:46 -0800, Andi Kleen wrote: 
> > > From: Andi Kleen <ak@...ux.intel.com>
> > > 
> > > This patch creates 4 new trace points: one at the beginning of idle,
> > > one before entering mwait, one after exiting mwait, and one after
> > > finishing the idle code. This is useful to trace down any
> > > additional latencies caused by the ever-growing idle code.
> > > 
> > > Idle latencies are a common source of performance problems, so it's
> > > important to be able to measure them.
> > 
> > You mean stuff like.. oh, say 60 cores doing zero work every 12ms
> > munching ~20% cpu?
> 
> Well that one is obvious. I mean more the subtle problems.

Yeah, not subtle.  SGI could use C2 as power supply stress tester.

-Mike

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