Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1760336AbZCZSSg (ORCPT ); Thu, 26 Mar 2009 14:18:36 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1754425AbZCZSR6 (ORCPT ); Thu, 26 Mar 2009 14:17:58 -0400 Received: from byss.tchmachines.com ([208.76.80.75]:51470 "EHLO byss.tchmachines.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754163AbZCZSR4 (ORCPT ); Thu, 26 Mar 2009 14:17:56 -0400 Date: Thu, 26 Mar 2009 11:17:47 -0700 From: Ravikiran G Thirumalai To: Ingo Molnar Cc: Jeremy Fitzhardinge , Yinghai Lu , Thomas Gleixner , "H. Peter Anvin" , Andrew Morton , "linux-kernel@vger.kernel.org" , shai@scalex86.org Subject: Re: [PATCH] x86: don't compile vsmp_64 for 32bit Message-ID: <20090326181747.GC10614@localdomain> References: <20090324061429.GH7278@localdomain> <20090324091035.GA6605@elte.hu> <20090325185138.GI7278@localdomain> <49CAAD2E.3060904@goop.org> <20090325223642.GK7278@localdomain> <49CABB25.8040106@goop.org> <20090325232921.GL7278@localdomain> <49CAC543.5020205@goop.org> <20090326003154.GA10614@localdomain> <20090326091153.GB9369@elte.hu> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20090326091153.GB9369@elte.hu> User-Agent: Mutt/1.5.15+20070412 (2007-04-11) X-AntiAbuse: This header was added to track abuse, please include it with any abuse report X-AntiAbuse: Primary Hostname - byss.tchmachines.com X-AntiAbuse: Original Domain - vger.kernel.org X-AntiAbuse: Originator/Caller UID/GID - [47 12] / [47 12] X-AntiAbuse: Sender Address Domain - scalex86.org Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1673 Lines: 46 On Thu, Mar 26, 2009 at 10:11:53AM +0100, Ingo Molnar wrote: > >* Ravikiran G Thirumalai wrote: > >> > unsynchronized_tsc() just returns a guess anyway, and if you >> > don't have X86_FEATURE_CONSTANT_TSC set, then it will return >> > unstable for your hardware anyway, even without the >> > is_vsmp_box() test. >> >> Unfortunately we use hardware which has X86_FEATURE_CONSTANT_TSC. >> >> > >> > Failing that, you could add yourself to bad_tsc_dmi_table[] and >> > have that mark the tsc as unstable (you have DMI, right?). >> > >> >> Newer versions of the VMM does, but older ones don't :(, and >> obviously we have older versions out in the field that still needs >> to be supported. > >But those old versions wont have X86_FEATURE_CONSTANT_TSC set, >right? No, the old versions also do have X86_FEATURE_CONSTANT_TSC. The kernel assumes that even netburst based cpus have synced tscs (of course this is never mentioned in the intel documentation, but in the past we've been told that that intel engineers say so -- that tscs are synced and guaranteed to not drift between intel cpus) Here's the code that sets X86_FEATURE_CONSTANT_TSC. static void __cpuinit early_init_intel(struct cpuinfo_x86 *c) { if ((c->x86 == 0xf && c->x86_model >= 0x03) || (c->x86 == 0x6 && c->x86_model >= 0x0e)) set_cpu_cap(c, X86_FEATURE_CONSTANT_TSC); ... Thanks, Kiran -- 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/