linux-kernel - RE: [PATCH 1/2] Define new percpu interface for shared data -- version 3

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Message-ID: <79E93560F4A5FD42BB769DAAF8BEF62A01AA8C77@scsmsx411.amr.corp.intel.com>
Date:	Wed, 23 May 2007 11:26:53 -0700
From:	"Yu, Fenghua" <fenghua.yu@...el.com>
To:	"Andrew Morton" <akpm@...ux-foundation.org>
Cc:	"Siddha, Suresh B" <suresh.b.siddha@...el.com>, <clameter@....com>,
	<kiran@...lex86.org>, <rmk@....linux.org.uk>,
	<linux-kernel@...r.kernel.org>
Subject: RE: [PATCH 1/2] Define new percpu interface for shared data -- version 3

> elements are cacheline aligned. And as such, this differentiates the
local
> only data and remotely accessed data cleanly.

>OK, but could we please have a concise description of the impact
>of these changes on kernel memory footprint?  Increase or decrease?
>And by approximately how much?

Depending on how linker places percpu data, the patches could
increase or decrease percpu section size. Data from 2.6.21-rc7-mm2:

On x86 SMP, the section size is increased from 0x7768 to 0x790c.
1.3% increase.

On X86-64 SMP, the size is decreased from 0x72d0 to 0x6540.
11.8% decrease.

On X86-64 VSMP, the size is increased from 0x72d0 to 0x8340.
14.3% increase.

On IA64 SMP, the size is decreased from 0x8370 to 0x7fc0.
2.8% decrease.
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