linux-kernel - Re: [patch] CFS scheduler, v3

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Message-ID: <20070420201101.GC5475@linux-os.sc.intel.com>
Date:	Fri, 20 Apr 2007 13:11:01 -0700
From:	"Siddha, Suresh B" <suresh.b.siddha@...el.com>
To:	William Lee Irwin III <wli@...omorphy.com>
Cc:	Christoph Lameter <clameter@....com>, Ingo Molnar <mingo@...e.hu>,
	linux-kernel@...r.kernel.org,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Con Kolivas <kernel@...ivas.org>,
	Nick Piggin <npiggin@...e.de>, Mike Galbraith <efault@....de>,
	Arjan van de Ven <arjan@...radead.org>,
	Peter Williams <pwil3058@...pond.net.au>,
	Thomas Gleixner <tglx@...utronix.de>, caglar@...dus.org.tr,
	Willy Tarreau <w@....eu>, Gene Heskett <gene.heskett@...il.com>
Subject: Re: [patch] CFS scheduler, v3

On Fri, Apr 20, 2007 at 01:03:22PM -0700, William Lee Irwin III wrote:
> On Fri, 20 Apr 2007, William Lee Irwin III wrote:
> >> I'm not really convinced it's all that worthwhile of an optimization,
> >> essentially for the same reasons as you, but presumably there's a
> >> benchmark result somewhere that says it matters. I've just not seen it.
> 
> On Fri, Apr 20, 2007 at 12:44:55PM -0700, Christoph Lameter wrote:
> > If it is true that we frequently remotely write the per cpu runqueue 
> > data then we may have a NUMA scalability issue.
> 
> From the discussion on Suresh's thread, it appears to have sped up a
> database benchmark 0.5%.
> 
> Last I checked it was workload-dependent, but there were things that
> hammer it. I mostly know of the remote wakeup issue, but there could
> be other things besides wakeups that do it, too.

remote wakeup was the main issue and the 0.5% improvement was seen
on a two node platform. Aligning it reduces the number of remote
cachelines that needs to be touched as part of this wakeup.

thanks,
suresh
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