From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756644Ab1EJPil (ORCPT ); Tue, 10 May 2011 11:38:41 -0400 Received: from s15228384.onlinehome-server.info ([87.106.30.177]:55388 "EHLO mail.x86-64.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756602Ab1EJPik (ORCPT ); Tue, 10 May 2011 11:38:40 -0400 Date: Tue, 10 May 2011 17:38:29 +0200 From: Borislav Petkov To: Greg KH Cc: Ben Hutchings , Borislav Petkov , "Rosenfeld, Hans" , "linux-kernel@vger.kernel.org" , "stable@kernel.org" , "akpm@linux-foundation.org" , "H. Peter Anvin" , "torvalds@linux-foundation.org" , "stable-review@kernel.org" , "alan@lxorguk.ukuu.org.uk" , "Ostrovsky, Boris" Subject: Re: [Stable-review] [12/28] x86, cpu: Clean up AMD erratum 400 workaround Message-ID: <20110510153829.GB3347@gere.osrc.amd.com> References: <1303265862.3464.77.camel@localhost> <20110420031105.GA11945@suse.de> <1303274910.3464.95.camel@localhost> <20110420050617.GA16756@suse.de> <1303356555.3464.128.camel@localhost> <20110505225302.GC12316@suse.de> <20110506074120.GB21046@liondog.tnic> <1305032339.4065.276.camel@localhost> <20110510140219.GB16789@aftab> <20110510151305.GA9824@suse.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20110510151305.GA9824@suse.de> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, May 10, 2011 at 08:13:05AM -0700, Greg KH wrote: > On Tue, May 10, 2011 at 04:02:19PM +0200, Borislav Petkov wrote: > > On Tue, May 10, 2011 at 08:58:59AM -0400, Ben Hutchings wrote: > > > I read that: > > > > > > " > > > Support for Always Running APIC timer (ARAT) was introduced in > > > commit db954b5898dd3ef3ef93f4144158ea8f97deb058. This feature > > > allows us to avoid switching timers from LAPIC to something else > > > (e.g. HPET) and go into timer broadcasts when entering deep > > > C-states. > > > > > > AMD processors don't provide a CPUID bit for that feature but > > > they also keep APIC timers running in deep C-states (except for > > > cases when the processor is affected by erratum 400). Therefore > > > we should set ARAT feature bit on AMD CPUs. > > > " > > > > > > This implies that the HPET was previously used during deep C-states, and > > > that all this erratum checking is about deciding whether the CPU has > > > ARAT. So what bug is being fixed by using ARAT instead of the HPET? > > > > That's a good question, actually. The original upstream commit > > b87cf80af3ba4b4c008b4face3c68d604e1715c6 wasn't tagged for stable and > > Boris O. didn't send it to stable either, as I'm being told. > > > > Maybe Greg has an idea? > > I added it because it was needed to get another errata patch to apply > properly, and I saw no reason not to apply other "quirks" like this to > older kernels, right? > > Or should I not have done that? Nah, I wouldn't say that. While this patch doesn't directly fix a regression, it does away with the erratum 400 workaround where we switch to HPET so it is more or less a regression fix for current and future machines which aren't affected by that erratum. Besides reading the LAPIC is much cheaper so we should be getting even a slight performance bump with it. So no, I don't see a problem with the patch being in stable. Thanks. -- Regards/Gruss, Boris. Advanced Micro Devices GmbH Einsteinring 24, 85609 Dornach General Managers: Alberto Bozzo, Andrew Bowd Registration: Dornach, Gemeinde Aschheim, Landkreis Muenchen Registergericht Muenchen, HRB Nr. 43632