Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1425642AbWLHQ5g (ORCPT ); Fri, 8 Dec 2006 11:57:36 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1425641AbWLHQ5g (ORCPT ); Fri, 8 Dec 2006 11:57:36 -0500 Received: from mx1.redhat.com ([66.187.233.31]:35849 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1425617AbWLHQ5f (ORCPT ); Fri, 8 Dec 2006 11:57:35 -0500 From: David Howells In-Reply-To: References: <20061206164314.19870.33519.stgit@warthog.cambridge.redhat.com> <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> To: Christoph Lameter Cc: Russell King , Nick Piggin , David Howells , 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 X-Mailer: MH-E 8.0; nmh 1.1; GNU Emacs 22.0.50 Date: Fri, 08 Dec 2006 16:56:57 +0000 Message-ID: <4595.1165597017@redhat.com> Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 790 Lines: 21 Christoph Lameter wrote: > cmpxchg is the simplest solution to realize many other atomic operations and > its widely available on a wide variety of platforms. But by no means all. Where it doesn't exist it can only be properly emulated by something such as LL/SC if they are there. If not, then you can't do a safe cmpxchg on SMP. > It is the most universal atomic instruction that I know of. I think TAS-type things and XCHG-type things are more common. In fact I think more things have LL/SC than have CMPXCHG. David - 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/