From: David Howells <dhowells@redhat.com>
To: Nick Piggin <npiggin@suse.de>
Cc: linux-arch@vger.kernel.org, linuxppc-dev@ozlabs.org,
paulus@samba.org, Ingo Molnar <mingo@elte.hu>
Subject: Re: [patch] mutex: optimise generic mutex implementations
Date: Wed, 22 Oct 2008 17:24:28 +0100 [thread overview]
Message-ID: <22459.1224692668@redhat.com> (raw)
In-Reply-To: <20081012054634.GA12535@wotan.suse.de>
Nick Piggin <npiggin@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@suse.de>
This seems to work on FRV which uses the mutex-dec generic algorithm, though
you have to take that with a pinch of salt as I don't have SMP hardware for
it.
Acked-by: David Howells <dhowells@redhat.com>
prev parent reply other threads:[~2008-10-22 16:24 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
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 [this message]
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