linux-kernel - Re: [tip:x86/asm] x86/defconfig: Turn on CONFIG_CC_OPTIMIZE_FOR

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Date:	Sat, 26 Jan 2013 07:18:26 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Borislav Petkov <bp@...en8.de>, mingo@...nel.org,
	linux-kernel@...r.kernel.org, torvalds@...ux-foundation.org,
	arjan@...ux.intel.com, jbeulich@...e.com, ling.ml@...pay.com,
	rostedt@...dmis.org, akpm@...ux-foundation.org, tglx@...utronix.de
CC:	linux-tip-commits@...r.kernel.org
Subject: Re: [tip:x86/asm] x86/defconfig: Turn on CONFIG_CC_OPTIMIZE_FOR_SIZE= y in the 64-bit defconfig

On the CPUs Ling is testing on the downsides of -Os probably matter less, in particular since rep movsb works well.

It is questionable as a generic default, though.

The whole -Ok discussion came from that.

Borislav Petkov <bp@...en8.de> wrote:

>On Sat, Jan 26, 2013 at 04:25:57AM -0800, tip-bot for Ma Ling wrote:
>> During the same  time (269.410275674 seconds) IPC from Os is
>> 0.37, O2 is 0.36, Os improved performance 2.7%.
>> 
>> Signed-off-by: Ma Ling <ling.ml@...pay.com>
>> Cc: Linus Torvalds <torvalds@...ux-foundation.org>
>> Cc: Arjan van de Ven <arjan@...ux.intel.com>
>> Cc: Andrew Morton <akpm@...ux-foundation.org>
>> Cc: Jan Beulich <jbeulich@...e.com>
>> Cc: Steven Rostedt <rostedt@...dmis.org>
>> Link:
>http://lkml.kernel.org/r/1359123061-6139-1-git-send-email-ling.ma@alipay.com
>> [ So, this is a bit symbolic as most people don't use the defconfig,
>>   but the measurements are useful nevertheless so let's commit this
>>   if there are no objections. ]
>
>What about
>
>commit 3a55fb0d9fe8e2f4594329edd58c5fd6f35a99dd
>Author: Kirill Smelkov <kirr@....spb.ru>
>Date:   Fri Nov 2 15:41:01 2012 +0400
>
>    Tell the world we gave up on pushing CC_OPTIMIZE_FOR_SIZE
>
>?
>
>Reportedly, -Os generates suboptimal code in certain cases and we
>advise
>against it with this patch.

-- 
Sent from my mobile phone. Please excuse brevity and lack of formatting.
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