From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753005AbZHaP7U (ORCPT ); Mon, 31 Aug 2009 11:59:20 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751427AbZHaP7U (ORCPT ); Mon, 31 Aug 2009 11:59:20 -0400 Received: from www.tglx.de ([62.245.132.106]:57598 "EHLO www.tglx.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751386AbZHaP7T (ORCPT ); Mon, 31 Aug 2009 11:59:19 -0400 Date: Mon, 31 Aug 2009 17:59:00 +0200 (CEST) From: Thomas Gleixner To: Martin Schwidefsky cc: mingo@redhat.com, hpa@zytor.com, linux-kernel@vger.kernel.org, johnstul@us.ibm.com, linux-tip-commits@vger.kernel.org Subject: Re: [tip:timers/core] clocksource: Resolve cpu hotplug dead lock with TSC unstable In-Reply-To: <20090831101928.4c00c797@skybase> Message-ID: References: <20090831101928.4c00c797@skybase> User-Agent: Alpine 2.00 (LFD 1167 2008-08-23) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, 31 Aug 2009, Martin Schwidefsky wrote: > Ah, very good. I've been going round in circles to find a solution that > allows to downgrade the tsc rating when the second cpu is enabled. > Could not find a solution. Your approach changes semantics slightly: > the tsc clock will continue with its old rating for a while until the > watchdog will do the downgrade. If that is acceptable then this is a > good solution. Even the old code did not switch right away. The TSC was used until the next timer interrupt. Also we survive the detection of unstable TSCs with the watchdog which can happen quite after the fact that it became unusable. The important point is that we detect it at all and replace it with something useable. Thanks, tglx