linux-kernel - RE: [PATCH 2/2] Call percpu smp cacheline algin interface

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Message-ID: <A29F7A5700A7EA4380E08C1F68C3B6D802B5F7CA@scsmsx411.amr.corp.intel.com>
Date:	Wed, 9 May 2007 16:10:05 -0700
From:	"Yu, Fenghua" <fenghua.yu@...el.com>
To:	"Christoph Lameter" <clameter@....com>,
	"Andrew Morton" <akpm@...ux-foundation.org>
CC:	"Siddha, Suresh B" <suresh.b.siddha@...el.com>,
	<linux-kernel@...r.kernel.org>
Subject: RE: [PATCH 2/2] Call percpu smp cacheline algin interface

On Wed, 9 May 2007, Andrew Morton wrote:

>> erm, it's not obviosu from all this that the patches are worth
proceeding
>> with, are they?

>What was it? 0.5% performance improvement on a synthetic benchmark? 
>Process wakeup I believe?

The initial patch and discussion is from:
http://www.uwsg.iu.edu/hypermail/linux/kernel/0704.1/0340.html

Yes, the runqueue patch has a 0.5% perf improvement on database
workload(which is a good improvement for this workload).

The theory behind the patches is:

1. Minimize number of cache lines that are touched during a remote
access. On Numa system, remote access is more expensive than local.
2. Do not share cache line between remote accessed data and local
accessed data. Local data update may cause remote access cache miss and
wait for longer time.

Although the patches themselves don't save or waste per_cpu size, the
above two reasons are good to have them in.

Thanks.

-Fenghua
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