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From: John Bradford <john@grabjohn.com>
To: alan@lxorguk.ukuu.org.uk, miller@techsource.com
Cc: bunk@fs.tum.de, linux-kernel@vger.kernel.org
Subject: Re: [2.6 patch] add an -Os config option
Date: Tue, 12 Aug 2003 20:43:57 +0100	[thread overview]
Message-ID: <200308121943.h7CJhvsa000910@81-2-122-30.bradfords.org.uk> (raw)

> >>+config OPTIMIZE_FOR_SIZE
> >>+	bool "Optimize for size" if EMBEDDED
> >>+	default n
> >>+	help
> >>+	  Enabling this option will pass "-Os" instead of "-O2" to gcc
> >>+	  resulting in a smaller kernel.
> >>+
> >>+	  The resulting kernel might be significantly slower.
> > 
> > 
> > With most of the gcc's I tried -Os was faster.
>
>
> Why is -Os faster?  Fewer cache misses?
>
> Wouldn't that make -O2 kinda pointless?  It seems kinda futile to 
> optimize for speed just to have it come out slower.

See the comments Linus made earlier this year on the same subject:

http://marc.theaimsgroup.com/?l=linux-kernel&m=104457390406050&w=2

Alan, could Valgrind help us to profile cache hits/misses in different
parts of the kernel?

John.

             reply	other threads:[~2003-08-12 19:32 UTC|newest]

Thread overview: 20+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2003-08-12 19:43 John Bradford [this message]
  -- strict thread matches above, loose matches on Subject: below --
2003-08-11 21:11 [2.6 patch] add an -Os config option Adrian Bunk
2003-08-11 21:19 ` Michael Buesch
2003-08-11 21:37   ` Mike Fedyk
2003-08-11 21:39   ` Christophe Saout
2003-08-11 21:41   ` Dagfinn Ilmari Mannsåker
2003-08-12  1:29   ` Gene Heskett
2003-08-12  2:51     ` Thomas Molina
2003-08-12 14:48       ` Gene Heskett
2003-08-12 10:11     ` Michael Buesch
2003-08-12 14:42       ` Gene Heskett
2003-08-12  1:45   ` Warren Turkal
2003-08-11 22:20 ` Russell King
2003-08-12  7:06 ` Christoph Hellwig
2003-08-12 15:43   ` Timothy Miller
2003-08-12 15:58     ` Adrian Bunk
2003-08-12 16:03     ` Kevin P. Fleming
2003-08-12 13:35 ` Alan Cox
2003-08-12 15:45   ` Joe Korty
2003-08-12 18:03   ` Timothy Miller

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