Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1760777AbWLHRSb (ORCPT ); Fri, 8 Dec 2006 12:18:31 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1760778AbWLHRSb (ORCPT ); Fri, 8 Dec 2006 12:18:31 -0500 Received: from caramon.arm.linux.org.uk ([217.147.92.249]:4488 "EHLO caramon.arm.linux.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1760777AbWLHRSa (ORCPT ); Fri, 8 Dec 2006 12:18:30 -0500 Date: Fri, 8 Dec 2006 17:18:17 +0000 From: Russell King To: Christoph Lameter Cc: David Howells , Nick Piggin , torvalds@osdl.org, akpm@osdl.org, linux-arm-kernel@lists.arm.linux.org.uk, linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org Subject: Re: [PATCH] WorkStruct: Implement generic UP cmpxchg() where an arch doesn't support it Message-ID: <20061208171816.GG31068@flint.arm.linux.org.uk> Mail-Followup-To: Christoph Lameter , David Howells , Nick Piggin , torvalds@osdl.org, akpm@osdl.org, linux-arm-kernel@lists.arm.linux.org.uk, linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org References: <20061206190025.GC9959@flint.arm.linux.org.uk> <20061206195820.GA15281@flint.arm.linux.org.uk> <4577DF5C.5070701@yahoo.com.au> <20061207150303.GB1255@flint.arm.linux.org.uk> <4578BD7C.4050703@yahoo.com.au> <20061208085634.GA25751@flint.arm.linux.org.uk> <4595.1165597017@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.4.2.1i Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1574 Lines: 42 On Fri, Dec 08, 2006 at 09:06:00AM -0800, Christoph Lameter wrote: > On Fri, 8 Dec 2006, David Howells wrote: > > > > It is the most universal atomic instruction that I know of. > > > > I think TAS-type things and XCHG-type things are more common. > > Huh? The most popular architectures are i386 x86_64 sparc ia64 etc which > all have one or the other form of cmpxchg (some issues with early sparc > and i386). According to the latest figures, 621 million ARM processors were shipped in Q3, which equates to about 78 processors per second. (taken from http://www.arm.com/news/15300.html). I'd like to know the figures for these other so-called "popular architectures". But in any case that's an utterly irrelevant point to the argument at hand. > > In fact I think more things have LL/SC than have CMPXCHG. > > LL/SC can be easily used to come up with a cmpxchg equivalent. As proven previously the reverse is also true. And as shown previously the cheaper out of the two for all platforms is the LL/SC based implementation, where the architecture specific implementation can be _either_ LL/SC based or cmpxchg based depending on what is supported in their hardware. I'm going to keep saying this until people get it. -- Russell King Linux kernel 2.6 ARM Linux - http://www.arm.linux.org.uk/ maintainer of: - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/