linux-kernel - Re: [PATCH v2] sched: Fast idling of CPU when system is partially loaded

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Message-ID: <20140623184757.GG13930@laptop.programming.kicks-ass.net>
Date:	Mon, 23 Jun 2014 20:47:57 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Andi Kleen <andi@...stfloor.org>
Cc:	Tim Chen <tim.c.chen@...ux.intel.com>, Ingo Molnar <mingo@...e.hu>,
	Michel Lespinasse <walken@...gle.com>,
	Rik van Riel <riel@...hat.com>,
	Peter Hurley <peter@...leysoftware.com>,
	Jason Low <jason.low2@...com>,
	Davidlohr Bueson <davidlohr@...com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] sched: Fast idling of CPU when system is partially
 loaded

On Mon, Jun 23, 2014 at 06:22:34PM +0200, Andi Kleen wrote:
> > So I don't get why we can't do the below; I think Jason tried to ask the
> > same...
> 
> The important part for performance is to minimize the cache line transfers. Your
> unconditional variant would cause more dirty cache lines than Tim's,
> right?

Don't think so. We already have the overloaded thing on stack and dirty,
and the only thing it needs is rq->nr_running and we already
unconditionally load that.
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