From: Nick Piggin <npiggin@suse.de>
To: Paul Mackerras <paulus@samba.org>
Cc: linux-arch@vger.kernel.org, linuxppc-dev@ozlabs.org,
Ingo Molnar <mingo@elte.hu>
Subject: Re: [patch] powerpc: implement optimised mutex fastpaths
Date: Thu, 6 Nov 2008 06:06:04 +0100 [thread overview]
Message-ID: <20081106050604.GA31556@wotan.suse.de> (raw)
In-Reply-To: <18706.28132.850598.687949@cargo.ozlabs.ibm.com>
On Thu, Nov 06, 2008 at 03:09:08PM +1100, Paul Mackerras wrote:
> Nick Piggin writes:
>
> > On Sun, Oct 12, 2008 at 07:47:32AM +0200, Nick Piggin wrote:
> > >
> > > Implement a more optimal mutex fastpath for powerpc, making use of acquire
> > > and release barrier semantics. This takes the mutex lock+unlock benchmark
> > > from 203 to 173 cycles on a G5.
> > >
> > > +static inline int
> > > +__mutex_fastpath_trylock(atomic_t *count, int (*fail_fn)(atomic_t *))
> > > +{
> > > + if (likely(__mutex_cmpxchg_lock(count, 1, 0) == 1))
> > > + return 1;
> >
> > Oops, I must have sent the wrong version. This needs a return 0 here.
>
> Are you going to send the right version? (or did you send it and I
> missed it?)
Hmm, I thought I did but perhaps not. Will do...
> Also I note that the comment you added just before that routine says:
>
> + * Change the count from 1 to a value lower than 1, and return 0 (failure)
> + * if it wasn't 1 originally, or return 1 (success) otherwise. This function
> + * MUST leave the value lower than 1 even when the "1" assertion wasn't true.
>
> yet just doing a __mutex_cmpxchg_lock isn't going to do that. So
> please fix either the comment or the code (or both :).
OK.
next prev parent reply other threads:[~2008-11-06 5:06 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2008-10-12 5:46 [patch] mutex: optimise generic mutex implementations Nick Piggin
2008-10-12 5:47 ` [patch] powerpc: implement optimised mutex fastpaths Nick Piggin
2008-10-13 1:18 ` Nick Piggin
2008-11-06 4:09 ` Paul Mackerras
2008-11-06 5:06 ` Nick Piggin [this message]
2008-10-13 16:15 ` Scott Wood
2008-10-13 16:20 ` Scott Wood
2008-10-14 7:06 ` Nick Piggin
2008-10-14 8:35 ` [patch] mutex: optimise generic mutex implementations Benjamin Herrenschmidt
2008-10-22 15:59 ` Ingo Molnar
2008-10-23 4:43 ` Benjamin Herrenschmidt
2008-10-23 7:02 ` Nick Piggin
2008-10-22 16:24 ` David Howells
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