From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S964800AbVLMKNp (ORCPT ); Tue, 13 Dec 2005 05:13:45 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S932601AbVLMKNp (ORCPT ); Tue, 13 Dec 2005 05:13:45 -0500 Received: from mx3.mail.elte.hu ([157.181.1.138]:54175 "EHLO mx3.mail.elte.hu") by vger.kernel.org with ESMTP id S932600AbVLMKNo (ORCPT ); Tue, 13 Dec 2005 05:13:44 -0500 Date: Tue, 13 Dec 2005 11:13:00 +0100 From: Ingo Molnar To: David Howells Cc: Nick Piggin , torvalds@osdl.org, akpm@osdl.org, hch@infradead.org, arjan@infradead.org, matthew@wil.cx, linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org Subject: Re: [PATCH 1/19] MUTEX: Introduce simple mutex implementation Message-ID: <20051213101300.GA2178@elte.hu> References: <439E122E.3080902@yahoo.com.au> <22479.1134467689@warthog.cambridge.redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <22479.1134467689@warthog.cambridge.redhat.com> User-Agent: Mutt/1.4.2.1i X-ELTE-SpamScore: 0.0 X-ELTE-SpamLevel: X-ELTE-SpamCheck: no X-ELTE-SpamVersion: ELTE 2.0 X-ELTE-SpamCheck-Details: score=0.0 required=5.9 tests=AWL autolearn=no SpamAssassin version=3.0.3 0.0 AWL AWL: From: address is in the auto white-list X-ELTE-VirusStatus: clean Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org * David Howells wrote: > Nick Piggin wrote: > > > We have atomic_cmpxchg. Can you use that for a sufficient generic > > implementation? > > No. CMPXCHG/CAS is not as available as XCHG, and it's also unnecessary. take a look at the PREEMPT_RT implementation of mutexes: it uses cmpxchg(), and thus both the down() and the up() fastpath is lockless! (And that is a mutex type that does alot more things, as it supports priority inheritance.) architectures which dont have cmpxchg can use a spinlock just fine. Ingo