From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755162Ab0EQK0i (ORCPT ); Mon, 17 May 2010 06:26:38 -0400 Received: from one.firstfloor.org ([213.235.205.2]:51138 "EHLO one.firstfloor.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751894Ab0EQK0h (ORCPT ); Mon, 17 May 2010 06:26:37 -0400 Date: Mon, 17 May 2010 12:26:35 +0200 From: Andi Kleen To: Dan Magenheimer Cc: Arjan van de Ven , Andi Kleen , Venkatesh Pallipadi , Ingo Molnar , Thomas Gleixner , "H. Peter Anvin" , chris.mason@oracle.com, linux-kernel@vger.kernel.org Subject: Re: [PATCH] x86: Export tsc related information in sysfs Message-ID: <20100517102635.GB20761@basil.fritz.box> References: <1273887635-27610-1-git-send-email-venki@google.com> <87tyq9mqrz.fsf@basil.nowhere.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.17 (2007-11-01) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org > Yes, understood. But the kernel doesn't expose a "gettimeofday > performance sucks" flag either. If it did (or in the case of > the patch, if tsc_reliable is zero) the application could at least > choose to turn off the 10000-100000 timestamps/second and log > a message saying "you are running on old hardware so you get > fewer features". I don't think anyone would object to exporting such a flag if it's cleanly designed. Getting the semantics right for that might be somewhat tricky though. How is "slow" defined? > A CPU-hotplugable system is a good example of a case where > the kernel should expose that tsc_reliable is 0. (I've heard That would mean that a large class of systems which are always hotplug capable (even if it's not used) would never get fast TSC time. Wasn't the goal here to be faster? > anecdotally that CPU hotplug into a QPI or Hypertransport system > will have some other interesting challenges, so may require some > special kernel parameters anyway.) Even if tsc_reliable were > only enabled if a "no-cpu_hotplug" kernel parameter is set, > that is still useful. And with cores-per-socket (and even > nodes-per-socket) going up seemingly every day, multi-socket > systems will likely be an ever smaller percentage of new > systems. Still the people running them will expect as good performance as possible. -Andi -- ak@linux.intel.com -- Speaking for myself only.