Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756793AbYFDBU2 (ORCPT ); Tue, 3 Jun 2008 21:20:28 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752751AbYFDBUU (ORCPT ); Tue, 3 Jun 2008 21:20:20 -0400 Received: from pentafluge.infradead.org ([213.146.154.40]:54450 "EHLO pentafluge.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752544AbYFDBUS (ORCPT ); Tue, 3 Jun 2008 21:20:18 -0400 Date: Tue, 3 Jun 2008 18:20:14 -0700 From: Arjan van de Ven To: akataria@vmware.com Cc: Thomas Gleixner , Ingo Molnar , LKML , Dan Hecht , Tim Mann , Zachary Amsden , Sahil Rihan Subject: Re: [RFC PATCH] x86:Use cpu_khz for loops_per_jiffy calculation Message-ID: <20080603182014.79a38d03@infradead.org> In-Reply-To: <1212540069.19290.57.camel@promb-2n-dhcp368.eng.vmware.com> References: <1212540069.19290.57.camel@promb-2n-dhcp368.eng.vmware.com> Organization: Intel X-Mailer: Claws Mail 3.3.1 (GTK+ 2.12.9; i386-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 pentafluge.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 Content-Length: 1252 Lines: 31 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.... 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) -- 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/