From: Andi Kleen <ak@suse.de>
To: Christoph Lameter <clameter@engr.sgi.com>
Subject: Re: [PATCH 1/5] cpuset memory spread basic implementation
Date: Tue, 7 Feb 2006 18:26:17 +0100
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Cc: Ingo Molnar <mingo@elte.hu>, Paul Jackson <pj@sgi.com>, akpm@osdl.org,
       dgc@sgi.com, steiner@sgi.com, Simon.Derr@bull.net,
       linux-kernel@vger.kernel.org
References: <20060204071910.10021.8437.sendpatchset@jackhammer.engr.sgi.com> <20060207123001.GA634@elte.hu> <Pine.LNX.4.62.0602070904460.24623@schroedinger.engr.sgi.com>
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On Tuesday 07 February 2006 18:06, Christoph Lameter wrote:
> On Tue, 7 Feb 2006, Ingo Molnar wrote:
> 
> > * Andi Kleen <ak@suse.de> wrote:
> > 
> > > I still don't really think it will make much difference if the file 
> > > cache is local or global. Compare to disk IO it is still infinitely 
> > > faster, so a relatively small slowdown from going off node is not that 
> > > big an issue.
> > 
> > well, maybe the SGI folks can give us some numbers?
> 
> The latency may grow (average) by a factor of 4 (same thoughput though on 
> our boxes). On some architectures it is significantly more and also the 
> bandwidth is reduced.
> 
> This is a significant factor. Applications that do not manage locality 
> correctly loose at least 30-40% performance.

This number is for local mapped memory I assume.

But do you have any numbers for file caches or dentry/inode caches? 
My guess is that if an  application would lose that much in read/write 
or readdir/stat it would call them too often :) But it's unlikely
i guess.

-Andi
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