Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752799AbYFDECI (ORCPT ); Wed, 4 Jun 2008 00:02:08 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1750781AbYFDEB4 (ORCPT ); Wed, 4 Jun 2008 00:01:56 -0400 Received: from wa-out-1112.google.com ([209.85.146.176]:14749 "EHLO wa-out-1112.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750765AbYFDEBz (ORCPT ); Wed, 4 Jun 2008 00:01:55 -0400 DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=message-id:date:from:to:subject:cc:in-reply-to:mime-version:content-type:content-transfer-encoding:content-disposition:references; b=lYllpyARQGSb0XaHATCQbOzYXlfFca+fxSy36JbNrx2HzdN3CNrRVLYR3MQZN2j2kIvN97N36SQcRc6ER9iE7w1nPs2YyPYvfzU/mBqNGSPkelCBRbODLJLD2a5VgvzuvX4/zyBISV6K2jPeEJ5ANlTjzfv3sDqJ3eKfG0r7+WU= Message-ID: <35f686220806032101h103152dat841818982aaa5052@mail.gmail.com> Date: Tue, 3 Jun 2008 21:01:54 -0700 From: "Alok kataria" To: "Arjan van de Ven" Subject: Re: [RFC PATCH] x86:Use cpu_khz for loops_per_jiffy calculation Cc: akataria@vmware.com, "Thomas Gleixner" , "Ingo Molnar" , LKML , "Dan Hecht" , "Tim Mann" , "Zachary Amsden" , "Sahil Rihan" In-Reply-To: <20080603182014.79a38d03@infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Content-Disposition: inline References: <1212540069.19290.57.camel@promb-2n-dhcp368.eng.vmware.com> <20080603182014.79a38d03@infradead.org> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2155 Lines: 55 On Tue, Jun 3, 2008 at 6:20 PM, Arjan van de Ven wrote: > On Tue, 03 Jun 2008 17:41:09 -0700 > Alok Kataria wrote: > >> On X86 platform we can use the value of cpu_khz computed during tsc >> calibration to calculate the loops_per_jiffy value. Its very >> important to keep the error in lpj values to minimum as any error in >> that may result in kernel panic in check_timer. >> In virtualization environment on a highly overloaded host, the guest >> delay calibration may sometimes result in errors beyond the ~50% that >> timer_irq_works can handle, resulting in the guest panicking. > \ > > can you guarantee that the rate tsc ticks at is the same as the current > CPU frequency? Answer: You can't.... > I think at the boot time atleast we can assume that, no ? If you are referring to the cpu frequency changing at run time (aka dynamic frequency scaling), in that case the time_cpufreq_notifier should take care of updating the loops_per_jiffy value for that corresponding cpu. > sadly we do need to calibrate this... > > In addition, clearly you can have different cpus in a system run at a > different rate (both in terms of cpu_khz and, independently, in terms > of tsc rate) > Again yes at run time frequency's may change but they shouldn't at boottime. AFAIK, i don't think there are X86 MP systems with asymmetric cpus i.e. systems with different base frequencies. If thats not true then there sure is a problem. Thanks, Alok > > -- > If you want to reach me at my work email, use arjan@linux.intel.com > For development, discussion and tips for power savings, > visit http://www.lesswatts.org > -- > 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/ > -- 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/