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

[Dimitrios Apostolou]

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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