From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754213AbbBKXKX (ORCPT ); Wed, 11 Feb 2015 18:10:23 -0500 Received: from mailhub.eng.utah.edu ([155.98.110.27]:42823 "EHLO mailhub.eng.utah.edu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752614AbbBKXKX (ORCPT ); Wed, 11 Feb 2015 18:10:23 -0500 Message-ID: <54DBE154.5040204@eng.utah.edu> Date: Wed, 11 Feb 2015 16:10:12 -0700 From: Scotty Bauer User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.4.0 MIME-Version: 1.0 To: "H. Peter Anvin" CC: tglx@linutronix.de, mingo@redhat.com, linux-kernel@vger.kernel.org, x86@kernel.org, Borislav Petkov Subject: Re: [PATCH] x86/smpboot: check if CLFLUSH is actually necessary References: <54CBF6F9.5040508@eng.utah.edu> <54DBCFD6.8000509@zytor.com> In-Reply-To: <54DBCFD6.8000509@zytor.com> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit X-UCE-Score: -1.9 (-) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 02/11/2015 02:55 PM, H. Peter Anvin wrote: > On 01/30/2015 01:26 PM, Scotty Bauer wrote: >> mwait_play_dead previously issued a CLFLUSH to work around a bug on >> some xeon processors. We can now determine if the CPU is a buggy CPU. >> This patch checks if if we're on a buggy CPU which allows non-buggy >> cpu's to eliminate the CLFLUSH. > Here is my first question: does this matter at all? Otherwise I don't > see a point. > > -hpa > > Do you get the same effect? Sure, but is the previous way the right way to do it? In my opinion no, but I'm not the one merging code its up to someone more experienced to determine if the change is warranted. The change is slightly faster on non-buggy cpu, but like you mention, is that relevant when the machine is going into idle?