linux-kernel - Re: -O0 kernel Re: High cpu temperature with 2.6.32, bisection shows commit 69d258 (fwd)

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Date:	Fri, 15 Jan 2010 22:40:39 +0200 (EET)
From:	Dimitrios Apostolou <jimis@....net>
To:	Pavel Machek <pavel@....cz>
cc:	Arjan van de Ven <arjan@...radead.org>,
	Alex Chiang <achiang@...com>, Len Brown <lenb@...nel.org>,
	Bjorn Helgaas <bjorn.helgaas@...com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Yinghai Lu <yinghai@...nel.org>, linux-kernel@...r.kernel.org
Subject: Re: -O0 kernel Re: High cpu temperature with 2.6.32, bisection shows
 commit 69d258 (fwd)

On Fri, 15 Jan 2010, Pavel Machek wrote:
>
>> BTW, how can I remove that irritating -O2 flag? I 'm used to compiling
>> with -O0 my debug builds in userland, because compilation is *many times*
>> faster. I should be really useful for bisections.
>
> Actually, figuring out kernel flags for fastest kernel compilation
> would be nice. Nice for bisect, and nice for slow machines. Zaurus
> needs 4 hours to compile kernel, kohjinsha cca 1.5 hours.
>
> -O0 may not fly, as inlining is needed... some tests are

I did some research too and this has been discussed again. Regarding 
inlining and -O0 I understand that theoretically it should work, but 
practically it doesn't. Here is an explanatory message from Andi Kleen:

http://lists.openwall.net/linux-kernel/2008/09/09/399

> neccessary. Now that we support icc, gcc -O0 should be doable, too...
>
> ...ok, so I tried -O0.
>
> -O2 compilation took 1250seconds, -O0 took 1167seconds and failed.
>
> is there some fast compiler around that could be used?

Strange that -O0 was not faster. Compiling userland I'm sure I've seen 
great speeds, and much less memory usage. Another compiler that is 
infamous for its speed is TCC (Tiny C Compiler) but I haven't actually 
used it, perhaps you want to try first. :-)


Dimitris

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