Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751199AbWCIR4p (ORCPT ); Thu, 9 Mar 2006 12:56:45 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751101AbWCIR4p (ORCPT ); Thu, 9 Mar 2006 12:56:45 -0500 Received: from smtp.osdl.org ([65.172.181.4]:46034 "EHLO smtp.osdl.org") by vger.kernel.org with ESMTP id S1751199AbWCIR4o (ORCPT ); Thu, 9 Mar 2006 12:56:44 -0500 Date: Thu, 9 Mar 2006 09:56:17 -0800 (PST) From: Linus Torvalds To: David Howells cc: Alan Cox , Pavel Machek , akpm@osdl.org, mingo@redhat.com, linux-arch@vger.kernel.org, linuxppc64-dev@ozlabs.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] Document Linux's memory barriers In-Reply-To: Message-ID: References: <1141855305.10606.6.camel@localhost.localdomain> <20060308161829.GC3669@elf.ucw.cz> <31492.1141753245@warthog.cambridge.redhat.com> <24309.1141848971@warthog.cambridge.redhat.com> <24280.1141904462@warthog.cambridge.redhat.com> <12101.1141925945@warthog.cambridge.redhat.com> 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: 759 Lines: 19 On Thu, 9 Mar 2006, Linus Torvalds wrote: > > So the fact that x86 SMP ops basically never guarantee any bus cycles > basically means that they are fundamentally no-ops when it comes to IO > serialization. That was really my only point. Side note: of course, locked cycles _do_ "serialize" the core. So they'll stop at least the core write merging, and speculative reads. So they do have some impact on IO, but they have no way of impacting things like write posting etc that is outside the CPU. 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/