Re: [2.6 patch] add a config option for -Os compilation

[Martin J. Bligh]

>> I really doubt it.  Kernel CPU footprint is dominated by dcache misses.  If
>> -Os reduces icache footprint it may even be a net win; people tend to
>> benchmark things in tight loops, which favours fast code over small code.
> 
> The main effect of -Os compared to -O2 (besides disabling some
> reordering of the code and prefetching) is the disabling of various
> alignments. I doubt that's a win on all CPUs.
> 
>> > - I've already seen a report for an ICE in gcc 2.95 of a user compiling
>> >   kernel 2.4 with -Os [1]
>> 
>> Well there's only one way to find out if we'll hit that.  How's about you
>> cook me a patch which switches to -Os unconditionally and we'll see how it
>> goes?
> 
> I still dislike it, but the patch is below.

Please don't - I benchmarked it a while ago, and it's definitely slower.
If you have a puny 128K L2 cache, it might help, but it definitely needs
to be optional.

M.

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