Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1426040AbWLHRZd (ORCPT ); Fri, 8 Dec 2006 12:25:33 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1426038AbWLHRZc (ORCPT ); Fri, 8 Dec 2006 12:25:32 -0500 Received: from omx2-ext.sgi.com ([192.48.171.19]:41383 "EHLO omx2.sgi.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1426035AbWLHRZb (ORCPT ); Fri, 8 Dec 2006 12:25:31 -0500 Date: Fri, 8 Dec 2006 09:23:57 -0800 (PST) From: Christoph Lameter To: Russell King 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 In-Reply-To: <20061208171816.GG31068@flint.arm.linux.org.uk> Message-ID: 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> <20061208171816.GG31068@flint.arm.linux.org.uk> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 964 Lines: 19 On Fri, 8 Dec 2006, Russell King wrote: > 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. As also shown in this thread: There are restrictions on what you can do between ll/sc. You would not want to use C code there. ll/sc is an thing that needs to be restricted to asm code. So this is not a viable proposal at all. ll/sc is useful to construct various atomic functions but cannot be directly used in C code. cmpxchg can be effectively realized using ll/sc. - 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/