Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752104AbWCOBZ1 (ORCPT ); Tue, 14 Mar 2006 20:25:27 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752112AbWCOBZ1 (ORCPT ); Tue, 14 Mar 2006 20:25:27 -0500 Received: from smtp107.mail.mud.yahoo.com ([209.191.85.217]:45995 "HELO smtp107.mail.mud.yahoo.com") by vger.kernel.org with SMTP id S1752104AbWCOBZ1 (ORCPT ); Tue, 14 Mar 2006 20:25:27 -0500 DomainKey-Signature: a=rsa-sha1; q=dns; c=nofws; s=s1024; d=yahoo.com.au; h=Received:Message-ID:Date:From:User-Agent:X-Accept-Language:MIME-Version:To:CC:Subject:References:In-Reply-To:Content-Type:Content-Transfer-Encoding; b=reLp/y4eQHFozRiPB44LmP88v7uKGT4s3QSIgV8iym64ZHz+BDdcaZzCtt8tyU69JlUTlodO4Wew1mJzxuo5WlhohrZ032rfU+28om1Oq3v1LaQVwxdMHIw5zzQT2M4U2MbinCcVYclPxU+L+FkCH8d4pzfzp8w2wCezECmsvco= ; Message-ID: <44176CF9.90909@yahoo.com.au> Date: Wed, 15 Mar 2006 12:25:13 +1100 From: Nick Piggin User-Agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.7.8) Gecko/20050927 Debian/1.7.8-1sarge3 X-Accept-Language: en MIME-Version: 1.0 To: Linus Torvalds CC: David Howells , Paul Mackerras , "Eric W. Biederman" , akpm@osdl.org, linux-arch@vger.kernel.org, linux-kernel@vger.kernel.org, mingo@redhat.com, alan@redhat.com, linuxppc64-dev@ozlabs.org Subject: Re: [PATCH] Document Linux's memory barriers [try #4] References: <17431.14867.211423.851470@cargo.ozlabs.ibm.com> <16835.1141936162@warthog.cambridge.redhat.com> <32068.1142371612@warthog.cambridge.redhat.com> <2301.1142380768@warthog.cambridge.redhat.com> In-Reply-To: Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1087 Lines: 31 Linus Torvalds wrote: > >On Tue, 14 Mar 2006, David Howells wrote: > >>But that doesn't make any sense! >> >>That would mean we that we'd've read b into d before having read the new value >>of p into q, and thus before having calculated the address from which to read d >>(ie: &b) - so how could we know we were supposed to read d from b and not from >>a without first having read p? >> >>Unless, of course, the smp_wmb() isn't effective, and the write to b happens >>after the write to p; or the Alpha's cache isn't fully coherent. >> > >The cache is fully coherent, but the coherency isn't _ordered_. > > This is what I was referring to when I said your (David's) idea of "memory" WRT memory consistency isn't correct -- cache coherency can be out of order. -- Send instant messages to your online friends http://au.messenger.yahoo.com - 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/