[patch] mutex: optimise generic mutex implementations

[Nick Piggin]

On Thu, Oct 23, 2008 at 03:43:58PM +1100, Benjamin Herrenschmidt wrote:
> On Wed, 2008-10-22 at 17:59 +0200, Ingo Molnar wrote:
> > * Nick Piggin <npiggin at suse.de> wrote:
> > 
> > > Speed up generic mutex implementations.
> > > 
> > > - atomic operations which both modify the variable and return something imply
> > >   full smp memory barriers before and after the memory operations involved
> > >   (failing atomic_cmpxchg, atomic_add_unless, etc don't imply a barrier because
> > >   they don't modify the target). See Documentation/atomic_ops.txt.
> > >   So remove extra barriers and branches.
> > >   
> > > - All architectures support atomic_cmpxchg. This has no relation to
> > >   __HAVE_ARCH_CMPXCHG. We can just take the atomic_cmpxchg path unconditionally
> > > 
> > > This reduces a simple single threaded fastpath lock+unlock test from 590 cycles
> > > to 203 cycles on a ppc970 system.
> > > 
> > > Signed-off-by: Nick Piggin <npiggin at suse.de>
> > 
> > no objections here. Lets merge these two patches via the ppc tree, so 
> > that it gets testing on real hardware as well?
> > 
> > Acked-by: Ingo Molnar <mingo at elte.hu>
> 
> Allright but in that case it will be after -rc1 unless I manage to sneak
> something in tomorrow before linux closes the merge window.
> 
> I can't get an update today.

Fine with me.

Thanks,
Nick