linux-kernel - Re: [PATCH RFC] [X86] performance improvement for memcpy

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Message-ID: <20091112121619.GD1394@ucw.cz>
Date:	Thu, 12 Nov 2009 13:16:19 +0100
From:	Pavel Machek <pavel@....cz>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	"H. Peter Anvin" <hpa@...or.com>, "Ma, Ling" <ling.ma@...el.com>,
	Ingo Molnar <mingo@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH RFC] [X86] performance improvement for memcpy_64.S by
	fast string.


> Ling, if you are interested, could you send a user-space test-app to 
> this thread that everyone could just compile and run on various older 
> boxes, to gather a performance profile of hand-coded versus string ops 
> performance?
> 
> ( And i think we can make a judgement based on cache-hot performance
>   alone - if then the strings ops will perform comparatively better in
>   cache-cold scenarios, so the cache-hot numbers would be a conservative
>   estimate. )

Ugh, really? I'd expect cache-cold performance to be not helped at all
(memory bandwidth limit) and you'll get slow down from additional
i-cache misses...
								Pavel

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