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Date: Tue, 24 Apr 2007 10:50:01 -0700
From: "Siddha, Suresh B" <suresh.b.siddha@intel.com>
To: Christoph Lameter <clameter@sgi.com>
Cc: "Siddha, Suresh B" <suresh.b.siddha@intel.com>,
       William Lee Irwin III <wli@holomorphy.com>, Ingo Molnar <mingo@elte.hu>,
       linux-kernel@vger.kernel.org,
       Linus Torvalds <torvalds@linux-foundation.org>,
       Andrew Morton <akpm@linux-foundation.org>,
       Con Kolivas <kernel@kolivas.org>, Nick Piggin <npiggin@suse.de>,
       Mike Galbraith <efault@gmx.de>, Arjan van de Ven <arjan@infradead.org>,
       Peter Williams <pwil3058@bigpond.net.au>,
       Thomas Gleixner <tglx@linutronix.de>, caglar@pardus.org.tr,
       Willy Tarreau <w@1wt.eu>, Gene Heskett <gene.heskett@gmail.com>
Subject: Re: [patch] CFS scheduler, v3
Message-ID: <20070424175001.GF5475@linux-os.sc.intel.com>
References: <Pine.LNX.4.64.0704201223280.21417@schroedinger.engr.sgi.com> <20070420192906.GB2986@holomorphy.com> <Pine.LNX.4.64.0704201231250.21514@schroedinger.engr.sgi.com> <20070420193856.GC2986@holomorphy.com> <Pine.LNX.4.64.0704201243280.21514@schroedinger.engr.sgi.com> <20070420200322.GD2986@holomorphy.com> <20070420201101.GC5475@linux-os.sc.intel.com> <Pine.LNX.4.64.0704241039110.8341@schroedinger.engr.sgi.com> <20070424174226.GE5475@linux-os.sc.intel.com> <Pine.LNX.4.64.0704241045160.8418@schroedinger.engr.sgi.com>
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On Tue, Apr 24, 2007 at 10:47:45AM -0700, Christoph Lameter wrote:
> On Tue, 24 Apr 2007, Siddha, Suresh B wrote:
> > Anyhow, this is a straight forward optimization and needs to be done. Do you
> > have any specific concerns?
> 
> Yes there should not be contention on per cpu data in principle. The 
> point of per cpu data is for the cpu to have access to contention free 
> cachelines.
> 
> If the data is contented then it should be moved out of per cpu data and properly 
> placed to minimize contention. Otherwise we will get into cacheline 
> aliases (__read_mostly in per cpu??) etc etc in the per cpu areas.

yes, we were planning to move this to a different percpu section, where
all the elements in this new section will be cacheline aligned(both
at the start, aswell as end)

thanks,
suresh