Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753547Ab1BNV3d (ORCPT ); Mon, 14 Feb 2011 16:29:33 -0500 Received: from hrndva-omtalb.mail.rr.com ([71.74.56.125]:57380 "EHLO hrndva-omtalb.mail.rr.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752918Ab1BNV3a (ORCPT ); Mon, 14 Feb 2011 16:29:30 -0500 X-Authority-Analysis: v=1.1 cv=3uSaImBeuprzHBlOOPjkqgu+7PcxSRW0m2Aphm9Zmck= c=1 sm=0 a=4UV-9Kl2S54A:10 a=Q9fys5e9bTEA:10 a=OPBmh+XkhLl+Enan7BmTLg==:17 a=4nhS0ASVNNpThf63vxYA:9 a=bsguCIjqvlTbnrEweIp5pdHNDFUA:4 a=PUjeQqilurYA:10 a=OPBmh+XkhLl+Enan7BmTLg==:117 X-Cloudmark-Score: 0 X-Originating-IP: 67.242.120.143 Subject: Re: [PATCH 0/2] jump label: 2.6.38 updates From: Steven Rostedt To: Peter Zijlstra Cc: Will Newton , Jason Baron , Mathieu Desnoyers , hpa@zytor.com, mingo@elte.hu, tglx@linutronix.de, andi@firstfloor.org, roland@redhat.com, rth@redhat.com, masami.hiramatsu.pt@hitachi.com, fweisbec@gmail.com, avi@redhat.com, davem@davemloft.net, sam@ravnborg.org, ddaney@caviumnetworks.com, michael@ellerman.id.au, linux-kernel@vger.kernel.org, Mike Frysinger , Chris Metcalf , dhowells , Martin Schwidefsky , "heiko.carstens" , benh In-Reply-To: <1297707868.5226.189.camel@laptop> References: <1297452328.5226.89.camel@laptop> <1297460297.5226.99.camel@laptop> <1297536465.5226.108.camel@laptop> <20110214155113.GA2840@redhat.com> <1297699024.2401.12.camel@twins> <20110214160437.GB2840@redhat.com> <1297700754.5226.110.camel@laptop> <20110214162947.GA3449@redhat.com> <1297701438.5226.113.camel@laptop> <1297702013.23343.51.camel@gandalf.stny.rr.com> <1297703892.23343.71.camel@gandalf.stny.rr.com> <1297704447.5226.127.camel@laptop> <1297705428.5226.142.camel@laptop> <1297707868.5226.189.camel@laptop> Content-Type: text/plain; charset="ISO-8859-15" Date: Mon, 14 Feb 2011 16:29:24 -0500 Message-ID: <1297718964.23343.75.camel@gandalf.stny.rr.com> Mime-Version: 1.0 X-Mailer: Evolution 2.30.3 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1112 Lines: 33 On Mon, 2011-02-14 at 19:24 +0100, Peter Zijlstra wrote: > On Mon, 2011-02-14 at 17:50 +0000, Will Newton wrote: > > > > It would observe a stale value, but that value would only be updated > > when the cache line was reloaded from main memory which would have to > > be triggered by either eviction or cache flushing. So it could get > > pretty stale. Whilst that's probably within the spec. of atomic_read I > > suspect it would lead to problems in practice. I could be wrong > > though. > > Right, so the typical scenario that could cause pain is something like: > > while (atomic_read(&foo) != n) > cpu_relax(); > > and the problem is that cpu_relax() doesn't know which particular > cacheline to flush in order to make things go faster, hm? But what about any global variable? Can't we also just have: while (global != n) cpu_relax(); ? -- Steve -- 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/