Re: [patch] i386: use C code for current_thread_info()

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In-Reply-To: <[email protected]>

On Sun, 11 Jun 2006 23:05:59 +0200, Emmanuel Fleury wrote:

> > Looking at the generated code, it seems the compiler just makes dumb
> > choices and tends to recompute current_thread_info() in unlikely code
> > paths even when there is no register pressure.  4.0.2 makes better
> > choices.
> What size with gcc 4.1.2 ? (just curiosity)

The 3.3 vs 4.0 comparisons were with two different configs, so only
relative gain/loss with asm vs. C could be compared.

I downloaded gcc 4.1.1 and compared to 4.0.2 with the exact same config,
since I was curious how much better it might be overall.

gcc 4.0.2:
   text	   data	    bss	    dec	    hex	filename
3645212	 555556	 312024	4512792	 44dc18	2.6.17-rc6-nb-C/vmlinux
3647276	 555556	 312024	4514856	 44e428	2.6.17-rc6-nb-asm/vmlinux

gcc 4.1.1:
   text	   data	    bss	    dec	    hex	filename
3614686	 520416	 311672	4446774	 43da36	2.6.17-rc6-nb-C/vmlinux
3616942	 520416	 311672	4449030	 43e306	2.6.17-rc6-nb-asm/vmlinux

Kernel code starts out ~30K bytes smaller with gcc 4.1 and using C
for current_thread_info() helps even more than with 4.0.  Nice...

Maybe a patch that enables C code for gcc 4.0+ would work, since
on 3.3 the asm code is better?

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