On Fri, Jun 28, 2013 at 01:19:48PM +0200, Ingo Molnar wrote:
>
> * Wedson Almeida Filho <wedso...@gmail.com> wrote:
>
> > The new implementation allows the compiler to better optimize the code; the
> > original implementation is still used when the kernel is compiled with older
> > versions of gcc that don't support asm-goto.
> >
> > Compiling with gcc 4.7.3, the original mutex_lock() is 60 bytes with the
> > fast
> > path taking 16 instructions; the new mutex_lock() is 42 bytes, with the fast
> > path taking 12 instructions.
> >
> > The original mutex_unlock() is 24 bytes with the fast path taking 7
> > instructions; the new mutex_unlock() is 25 bytes (because the compiler used
> > a 2-byte ret) with the fast path taking 4 instructions.
> >
> > The two versions of the functions are included below for reference.
Btw, do we have any perf data showing any improvements from this patch?
[ … ]
> One detail:
>
> > +#if defined(CC_HAVE_ASM_GOTO)
> > +#if defined(CC_HAVE_ASM_GOTO)
>
> Please change these to #ifdef.
Cool - so we have a scripts/gcc-goto.sh which checks for support
for asm goto.
Our testing for asm goto otherwise is a bit more, hmm, hands-on in
arch/x86/include/asm/cpufeature.h:
#if __GNUC__ > 4 || __GNUC_MINOR__ >= 5
Maybe I should change that to the more explicit CC_HAVE_ASM_GOTO then.
--
Regards/Gruss,
Boris.
Sent from a fat crate under my desk. Formatting is fine.
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