Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S937866AbWLGAzK (ORCPT ); Wed, 6 Dec 2006 19:55:10 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S937869AbWLGAzJ (ORCPT ); Wed, 6 Dec 2006 19:55:09 -0500 Received: from smtp.osdl.org ([65.172.181.25]:60470 "EHLO smtp.osdl.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S937866AbWLGAzH (ORCPT ); Wed, 6 Dec 2006 19:55:07 -0500 Date: Wed, 6 Dec 2006 16:54:30 -0800 (PST) From: Linus Torvalds To: Roman Zippel cc: Matthew Wilcox , Christoph Lameter , David Howells , 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: Message-ID: References: <20061206164314.19870.33519.stgit@warthog.cambridge.redhat.com> <20061206190025.GC9959@flint.arm.linux.org.uk> <20061206195820.GA15281@flint.arm.linux.org.uk> <20061206213626.GE3013@parisc-linux.org> <20061206220532.GF3013@parisc-linux.org> 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: 1530 Lines: 35 On Thu, 7 Dec 2006, Roman Zippel wrote: > On Wed, 6 Dec 2006, Matthew Wilcox wrote: > > > To be honest, it'd be much easier if we only defined these operations on > > atomic_t's. We have all the infrastructure in place for them, and > > they're fairly well understood. If you need different sizes, I'm OK > > with an atomic_pointer_t, or whatever. > > FWIW Seconded. I disagree. Any _real_ CPU will simply never care about _anything_ else than just the size of the datum in question. There's absolutely no point to only allow it on certain types, especially as we _know_ those certain types are already going to be more than one, and we also know that they are going to be different sizes. In other words, in reality, we have to handle a sizeable subset of the whole generic situation, and the "on certain types only" situation is only going to be awkward and irritating. For example, would we have a different "cmpxchg_ptr()" function for the atomic pointer thing? With any reasonable CPU just depending on the _size_ of the type, I don't see what the problem is with just doing the bog-standard "cmpxchg_8/16/32/64" and having the bog-standard case- statement in a header file to do it all automatically for you, and then we don't need to worry about it. Linus - 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/