Messages in this thread | | | Date | Fri, 28 Jun 2013 16:09:38 +0200 | From | Borislav Petkov <> | Subject | Re: [PATCH] x86: Use asm-goto to implement mutex fast path on x86-64 |
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On Fri, Jun 28, 2013 at 01:19:48PM +0200, Ingo Molnar wrote: > > * Wedson Almeida Filho <wedsonaf@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?
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> 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.
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