linux-kernel - Re: -Os versus -O2

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Message-ID: <20070625014627.GC1094@stusta.de>
Date:	Mon, 25 Jun 2007 03:46:28 +0200
From:	Adrian Bunk <bunk@...sta.de>
To:	Jeff Garzik <jeff@...zik.org>
Cc:	Arjan van de Ven <arjan@...radead.org>,
	Benjamin LaHaise <bcrl@...ck.org>,
	Oleg Verych <olecom@...wer.upol.cz>, rae l <crquan@...il.com>,
	linux-kernel@...r.kernel.org
Subject: Re: -Os versus -O2

On Sun, Jun 24, 2007 at 09:34:05PM -0400, Jeff Garzik wrote:
> Adrian Bunk wrote:
>> The interesting questions are:
>> Does -Os still sometimes generate faster code with gcc 4.2?
>> If yes, why?
>
> Smaller code can mean fewer page faults, fewer cache invalidations, etc.
>
> It's not just a matter of compiler code generation, gotta look at the whole 
> picture.

Sure, but my point is that if the kernel is considered special and the 
best optimization for the kernel is therefore between -Os and -O2, we 
should try to find this point of best optimization.

This should address Arjans point that -Os might not be best choice for 
best performance (and it's actually our fault if gcc generates stupid 
but small code when we use -Os).

> 	Jeff

cu
Adrian

-- 

       "Is there not promise of rain?" Ling Tan asked suddenly out
        of the darkness. There had been need of rain for many days.
       "Only a promise," Lao Er said.
                                       Pearl S. Buck - Dragon Seed

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