Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753152AbXI1RND (ORCPT ); Fri, 28 Sep 2007 13:13:03 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751359AbXI1RMv (ORCPT ); Fri, 28 Sep 2007 13:12:51 -0400 Received: from outpipe-village-512-1.bc.nu ([81.2.110.250]:47910 "EHLO the-village.bc.nu" rhost-flags-OK-FAIL-OK-FAIL) by vger.kernel.org with ESMTP id S1751146AbXI1RMv (ORCPT ); Fri, 28 Sep 2007 13:12:51 -0400 Date: Fri, 28 Sep 2007 18:18:31 +0100 From: Alan Cox To: Nick Piggin Cc: Linux Kernel Mailing List , Linus Torvalds , Andi Kleen Subject: Re: [patch] x86: improved memory barrier implementation Message-ID: <20070928181831.26f34a64@the-village.bc.nu> In-Reply-To: <20070928165425.GA7366@wotan.suse.de> References: <20070928154832.GB12538@wotan.suse.de> <20070928170719.2f617a7a@the-village.bc.nu> <20070928165425.GA7366@wotan.suse.de> X-Mailer: Claws Mail 2.10.0 (GTK+ 2.10.14; i386-redhat-linux-gnu) Organization: Red Hat UK Cyf., Amberley Place, 107-111 Peascod Street, Windsor, Berkshire, SL4 1TE, Y Deyrnas Gyfunol. Cofrestrwyd yng Nghymru a Lloegr o'r rhif cofrestru 3798903 Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1230 Lines: 27 > on the broken ppro stores config option if you just tell me what should > be there (again, remember that my patch isn't actually changing anything > already there except for smp_rmb side). The PPro needs rmb to ensure a store doesn't go for a walk on the wild side and pass the read especially when we are dealing with device space. The rest of the stuff is a little vague which makes me nervous when considering relaxing the PPro case for smp_rmb. With smp_rmb as it is at the moment the PPro is effectively treated as an out of order cpu and so shouldn't hit anything occassionally that a PPC wouldn't hit every time. > > - and for modern processors its still not remotely clear your patch is > > correct because of NT stores. > > No. We already _have_ to rely on this model for barriers Well Linus has dealt with the question of NT stores for us now... Given this isn't an issue on 64bit I'm inclined to argue that only 64bit behaviour should be changed at this point. Alan - 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/