netdev - Re: [PATCH] tg3 : avoid an expensive divide

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Message-Id: <20070207.014514.132928442.davem@davemloft.net>
Date:	Wed, 07 Feb 2007 01:45:14 -0800 (PST)
From:	David Miller <davem@...emloft.net>
To:	ak@...e.de
Cc:	dada1@...mosbay.com, mchan@...adcom.com, netdev@...r.kernel.org
Subject: Re: [PATCH] tg3 : avoid an expensive divide

From: Andi Kleen <ak@...e.de>
Date: 07 Feb 2007 10:54:49 +0100

> Probably Eric compiled with the now default CONFIG_CC_OPTIMIZE_FOR_SIZE/-Os.
> With that gcc decides to use the shorter hardware divide instruction, even
> though it is significantly slower than an expanded optimized sequence
> for constant dividend.
> 
> We've seen this in a few other cases while during performance regression
> testing between kernels that still used -O2 vs the newer -Os.
> 
> No good solution found unfortunately.

Thanks for the explanation, that makes a lot of sense.
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