Re: Compiling packages for the standard distribution with -Os instead of -O2
Anthony DeRobertis wrote:
> On Wed, May 03, 2006 at 11:02:57AM -0300, Henrique de Moraes Holschuh wrote:
>
> > For Etch and Sid, it is probably a good idea to use -Os instead of -O2 at
> > least on the bigger arches (ia32, ia64, amd64, etc), as we can probably
> > trust gcc not to screw up.
>
> If gcc generally generates faster code with -Os than -O2, then isn't
> that a gcc bug,
It doesn't do so generally.
>in that the optimizations enabled by -O2 are incorrectly picked?
The compiler can only make some broad assumptions about the CPU's
memory/cache system, and none about the size of the working set.
If the working set with -O2 spills out of the cache but doesn't with
-Os then you get a performance improvement from -Os, for the next CPU
with bigger caches it can swing back.
> [Also, are there that man AMD64 machines with limited memory? Or IA64?]
Swap is now mostly irrelevant for performance discussions, if you hit
swap you won't have performance anyway. :-)
Thiemo
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