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Re: [PATCH] Reimplement clear_page/copy_page

To: Thiemo Seufer <ths@networkno.de>
Subject: Re: [PATCH] Reimplement clear_page/copy_page
From: Ralf Baechle <ralf@linux-mips.org>
Date: Mon, 18 Feb 2008 21:28:23 +0000
Cc: linux-mips@linux-mips.org
In-reply-to: <20080218193249.GD4747@networkno.de>
Original-recipient: rfc822;linux-mips@linux-mips.org
References: <20080218193249.GD4747@networkno.de>
Sender: linux-mips-bounce@linux-mips.org
User-agent: Mutt/1.5.17 (2007-11-01)
On Mon, Feb 18, 2008 at 07:32:49PM +0000, Thiemo Seufer wrote:

> Fold the SB-1 specific implementation of clear_page/copy_page in the
> generic version, and rewrite that one in tlbex style. The immediate
> benefits:
>   - It converts the compile-time workaround for SB-1 pass 1 prefetches
>     to a more efficient run-time check.
>   - It allows adjustment of loop unfolling, which helps to reduce the
>     number of redundant cdex cache ops.
>   - It fixes some esoteric cornercases (the cache line length calculations
>     can go wrong, and support for 64k pages without prefetch instructions
>     will overflow the addiu immediate).
>   - Somewhat better guesses of "good" prefetch values.
> 
> 
> Signed-off-by: Thiemo Seufer <ths@networkno.de>
> ---
> 
> Lmbench3 running on a BCM1480 system shows improvements for some
> benchmarks (three runs with the original kernel, then three runs
> with the patched kernel), most markedly (~5%) for open/close and
> exec:

The patch is certainly a good thing but I somehow doubt for many of the
improvments that they are a result of the patch and not the unavoidable
benchmarking noise.

Queued for 2.6.26,

  Ralf

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