From mboxrd@z Thu Jan 1 00:00:00 1970 From: Nick Piggin Subject: Re: [patch] mutex: optimise generic mutex implementations Date: Thu, 23 Oct 2008 09:02:08 +0200 Message-ID: <20081023070207.GA30765@wotan.suse.de> References: <20081012054634.GA12535@wotan.suse.de> <20081022155923.GM23060@elte.hu> <1224737038.7654.385.camel@pasglop> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Received: from cantor2.suse.de ([195.135.220.15]:48283 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750785AbYJWHCK (ORCPT ); Thu, 23 Oct 2008 03:02:10 -0400 Content-Disposition: inline In-Reply-To: <1224737038.7654.385.camel@pasglop> Sender: linux-arch-owner@vger.kernel.org List-ID: To: Benjamin Herrenschmidt Cc: Ingo Molnar , linux-arch@vger.kernel.org, linuxppc-dev@ozlabs.org, paulus@samba.org, Peter Zijlstra 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 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 > > > > 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 > > 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