From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752166Ab0IAFbI (ORCPT ); Wed, 1 Sep 2010 01:31:08 -0400 Received: from mx3.mail.elte.hu ([157.181.1.138]:48331 "EHLO mx3.mail.elte.hu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751132Ab0IAFbG (ORCPT ); Wed, 1 Sep 2010 01:31:06 -0400 Date: Wed, 1 Sep 2010 07:30:55 +0200 From: Ingo Molnar To: Don Zickus Cc: peterz@infradead.org, gorcunov@gmail.com, fweisbec@gmail.com, linux-kernel@vger.kernel.org Subject: Re: [PATCH 1/3] [lockup detector] sync touch_*_watchdog back to old semantics Message-ID: <20100901053055.GA14316@elte.hu> References: <1283310009-22168-1-git-send-email-dzickus@redhat.com> <1283310009-22168-2-git-send-email-dzickus@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1283310009-22168-2-git-send-email-dzickus@redhat.com> User-Agent: Mutt/1.5.20 (2009-08-17) X-ELTE-SpamScore: -2.0 X-ELTE-SpamLevel: X-ELTE-SpamCheck: no X-ELTE-SpamVersion: ELTE 2.0 X-ELTE-SpamCheck-Details: score=-2.0 required=5.9 tests=BAYES_00 autolearn=no SpamAssassin version=3.2.5 -2.0 BAYES_00 BODY: Bayesian spam probability is 0 to 1% [score: 0.0000] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org * Don Zickus wrote: > void touch_nmi_watchdog(void) > { > - __get_cpu_var(watchdog_nmi_touch) = true; > + if (watchdog_enabled) { > + unsigned cpu; > + > + for_each_present_cpu(cpu) { > + if (per_cpu(watchdog_nmi_touch, cpu) != true) > + per_cpu(watchdog_nmi_touch, cpu) = true; > + } Hm, this is going to be a scalability nightmare with lots of CPUs. Not only do we have a nr_cpus loop, but we touch per-cpu areas of _other_ CPUs - a big scalability nono. Why do we need to do this? We never needed to touch other CPU's NMI lockup accounting data areas - why has this changed? The changelog does not explain this. Thanks, Ingo