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Subject: RE: [PATCH 1/2] Define new percpu interface for shared data -- version 3
Date: Wed, 23 May 2007 11:26:53 -0700
Message-ID: <79E93560F4A5FD42BB769DAAF8BEF62A01AA8C77@scsmsx411.amr.corp.intel.com>
In-Reply-To: <20070523104946.f279241c.akpm@linux-foundation.org>
Thread-Topic: [PATCH 1/2] Define new percpu interface for shared data -- version 3
Thread-Index: AcedYsn36XFq/U8/RzWdd8giGOkWvQAARGIg
From: "Yu, Fenghua" <fenghua.yu@intel.com>
To: "Andrew Morton" <akpm@linux-foundation.org>
Cc: "Siddha, Suresh B" <suresh.b.siddha@intel.com>, <clameter@sgi.com>,
       <kiran@scalex86.org>, <rmk@arm.linux.org.uk>,
       <linux-kernel@vger.kernel.org>
Sender: linux-kernel-owner@vger.kernel.org
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> 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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