From mboxrd@z Thu Jan 1 00:00:00 1970 From: Ingo Molnar Subject: Re: smp.c && barriers (Was: [PATCH 1/4] generic-smp: remove single ipi fallback for smp_call_function_many()) Date: Fri, 20 Feb 2009 20:40:54 +0100 Message-ID: <20090220194054.GA2444@elte.hu> References: <20090217112657.GE26402@wotan.suse.de> <1234923702.29823.7.camel@vayu> <20090218135945.GC23125@wotan.suse.de> <1234982620.29823.22.camel@vayu> <20090218191757.GD8889@elte.hu> <1235001314.14523.2.camel@vayu> <20090219122031.GC1703@elte.hu> <1235080824.14523.19.camel@vayu> <20090220105640.GE28581@elte.hu> <1235156214.14523.54.camel@vayu> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Received: from mx3.mail.elte.hu ([157.181.1.138]:60409 "EHLO mx3.mail.elte.hu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751032AbZBTTlk (ORCPT ); Fri, 20 Feb 2009 14:41:40 -0500 Content-Disposition: inline In-Reply-To: <1235156214.14523.54.camel@vayu> Sender: linux-arch-owner@vger.kernel.org List-ID: To: Suresh Siddha Cc: Nick Piggin , Peter Zijlstra , Oleg Nesterov , Jens Axboe , Linus Torvalds , "Paul E. McKenney" , Rusty Russell , Steven Rostedt , "linux-kernel@vger.kernel.org" , "linux-arch@vger.kernel.org" , steiner@sgi.com * Suresh Siddha wrote: > > So the question is, is an SFENCE there enough to serialize > > the WRMSR with previous memory-writes? It's not specified in > > the x2apic docs as far as i could see. > > No. sfence is not enough (wrmsr to x2apic regs was still > passing ahead). We have done a small experiment to demonstrate > the issue and adding mfence fixes the issue but not sfence. We > need a serializing instruction or mfence. I will try to get > the SDM updated. Fair enough! Ingo