Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759729AbXFFIzG (ORCPT ); Wed, 6 Jun 2007 04:55:06 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1754719AbXFFIy4 (ORCPT ); Wed, 6 Jun 2007 04:54:56 -0400 Received: from 207.47.60.4.static.nextweb.net ([207.47.60.4]:60926 "EHLO rpc.xensource.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1753138AbXFFIyz (ORCPT ); Wed, 6 Jun 2007 04:54:55 -0400 User-Agent: Microsoft-Entourage/11.3.3.061214 Date: Wed, 06 Jun 2007 09:54:51 +0100 Subject: Re: [Xen-devel] [patch 14/33] xen: xen time implementation From: Keir Fraser To: Jan Beulich , Jeremy Fitzhardinge CC: Xen-devel , Andrew Morton , Andi Kleen , lkml , Chris Wright , , Ingo Molnar , Linus Torvalds , Thomas Gleixner Message-ID: Thread-Topic: [Xen-devel] [patch 14/33] xen: xen time implementation Thread-Index: AceoGFfalk+8WBQLEdyEZAAX8io7RQ== In-Reply-To: <46668EC6.76E4.0078.0@novell.com> Mime-version: 1.0 Content-type: text/plain; charset="US-ASCII" Content-transfer-encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1152 Lines: 23 On 6/6/07 09:39, "Jan Beulich" wrote: > The issue is > that on that system, transition into ACPI mode takes over 600ms (SMM > execution, and hence no interrupts delivered during that time), and with > Xen using the PIT (PM timer support was added by Keir as a result of this, > but that doesn't cure the problem here, it just reduces the likelihood it'll > be encountered) platform time and local time got pretty much out of sync. If you have an ACPI PM timer in your system (and if you have SMM then your system is almost certainly modern enough to have one) then surely the problem is fixed for all practical purposes? The problem was overflow of a fixed-width platform counter. The PIT wraps every ~50ms, but the ACPI PM timer will wrap only every ~4s. It would be quite unreasonable for SMM to take the CPU away for multiple seconds, even as a one-time boot operation. -- Keir - 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/