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

[Andrew Morton]

Adrian Bunk <bunk@xxxxxxxxx> wrote:
>
> On Wed, Oct 15, 2003 at 04:12:51PM -0700, Andrew Morton wrote:
> >...
> > They are small concerns really, but it does make one wonder why we should
> > not make this change unconditional: just switch the kernel to -Os?
> > 
> > Does anyone have any (non-micro-)benchmark results which say this is a bad
> > idea?
> 
> No benchmarks, only arguments:
> 
> - it's less tested (there might be miscompilations in some part of the 
>   kernel with some supported compilers)

Testing is not a problem.

> - there might be fast path code somewhere in the kernel that becomes
>   significantely slower with -Os

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.

> - 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?

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