From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753250Ab0EPU0r (ORCPT ); Sun, 16 May 2010 16:26:47 -0400 Received: from casper.infradead.org ([85.118.1.10]:42493 "EHLO casper.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752474Ab0EPU0q (ORCPT ); Sun, 16 May 2010 16:26:46 -0400 Date: Sun, 16 May 2010 13:29:33 -0700 From: Arjan van de Ven To: Dan Magenheimer Cc: Thomas Gleixner , Andi Kleen , Venkatesh Pallipadi , Ingo Molnar , "H. Peter Anvin" , chris.mason@oracle.com, linux-kernel@vger.kernel.org Subject: Re: [PATCH] x86: Export tsc related information in sysfs Message-ID: <20100516132933.617d1544@infradead.org> In-Reply-To: References: <1273887635-27610-1-git-send-email-venki@google.com> <87tyq9mqrz.fsf@basil.nowhere.org> <35aa841b-e151-424d-b1c1-0c03dbcae5cc@default> <20100515121424.38f5b389@infradead.org> <20100515224305.17a04022@infradead.org alpine.LFD.2.00.1005161113450.3199@localhost.localdomain> Organization: Intel X-Mailer: Claws Mail 3.7.5 (GTK+ 2.16.6; i586-redhat-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-SRS-Rewrite: SMTP reverse-path rewritten from by casper.infradead.org See http://www.infradead.org/rpr.html Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sun, 16 May 2010 09:42:40 -0700 (PDT) Dan Magenheimer wrote: > > From: Thomas Gleixner [mailto:tglx@linutronix.de] > > Nah, there are systems which will have it set to 1: > > Dig out your good old Pentium-I box and enjoy. > > Hot stove syndrome again? Are you truly saying that there > are NO single-socket multi-core systems that don't have > stupid firmware (SMI and/or BIOS)? there are no systems *where we can know* this. Some of the stupid SMI only triggers on higher temperature situations etc. Impossible to know upfront. > If things are this bad, why on earth would the kernel itself > EVER use TSC even as its own internal clocksource? Why do you think we do extensive and continuous validation of the tsc (and soon, continuous recalibration) > But that doesn't mean the vast majority of latest generation > single-socket systems can't set "tsc_reliable" to 1. Or that > the kernel is responsible for detecting and/or correcting > every system with buggy firmware. sadly this also shows up on single socket systems... much more than we like. This is why I really really hate having apps run tsc directly. A VDSO call at least gives the kernel the option to ensure correctness... even if it starts out fast and goes slow suddenly after 3 weeks when the AC in the datacenter got maintenance for an hour. -- Arjan van de Ven Intel Open Source Technology Centre For development, discussion and tips for power savings, visit http://www.lesswatts.org