Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758700AbaGXLSI (ORCPT ); Thu, 24 Jul 2014 07:18:08 -0400 Received: from mx6-phx2.redhat.com ([209.132.183.39]:41307 "EHLO mx6-phx2.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752666AbaGXLSG (ORCPT ); Thu, 24 Jul 2014 07:18:06 -0400 Date: Thu, 24 Jul 2014 07:18:05 -0400 (EDT) From: Ulrich Obergfell To: Paolo Bonzini Cc: Andrew Jones , linux-kernel@vger.kernel.org, kvm@vger.kernel.org, dzickus@redhat.com, akpm@linux-foundation.org, mingo@redhat.com Message-ID: <1140033921.17233579.1406200685037.JavaMail.zimbra@redhat.com> In-Reply-To: <53D0E3F3.6050206@redhat.com> References: <1406196811-5384-1-git-send-email-drjones@redhat.com> <1406196811-5384-3-git-send-email-drjones@redhat.com> <53D0E3F3.6050206@redhat.com> Subject: Re: [PATCH 2/3] watchdog: control hard lockup detection default MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit X-Originating-IP: [10.5.82.7] X-Mailer: Zimbra 8.0.6_GA_5922 (ZimbraWebClient - FF22 (Linux)/8.0.6_GA_5922) Thread-Topic: watchdog: control hard lockup detection default Thread-Index: HiZCwsNMPv2nFG98L0gT5mCO8QG/PA== Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org > ----- Original Message ----- > From: "Paolo Bonzini" > To: "Andrew Jones" , linux-kernel@vger.kernel.org, kvm@vger.kernel.org > Cc: uobergfe@redhat.com, dzickus@redhat.com, akpm@linux-foundation.org, mingo@redhat.com > Sent: Thursday, July 24, 2014 12:46:11 PM > Subject: Re: [PATCH 2/3] watchdog: control hard lockup detection default > >Il 24/07/2014 12:13, Andrew Jones ha scritto: >> >> The running kernel still has the ability to enable/disable at any >> time with /proc/sys/kernel/nmi_watchdog us usual. However even >> when the default has been overridden /proc/sys/kernel/nmi_watchdog >> will initially show '1'. To truly turn it on one must disable/enable >> it, i.e. >> echo 0 > /proc/sys/kernel/nmi_watchdog >> echo 1 > /proc/sys/kernel/nmi_watchdog > > Why is it hard to make this show the right value? :) > > Paolo 'echo 1 > /proc/sys/kernel/nmi_watchdog' enables both - hard lockup and soft lockup detection. watchdog_enable_all_cpus() starts a 'watchdog/N' thread for each CPU. If the kernel runs on a bare metal system where the processor does not have a PMU, or when perf_event_create_kernel_counter() returns failure to watchdog_nmi_enable(), or when the kernel runs as a guest on a hypervisor that does not emulate a PMU, then the 'watchdog/N' threads are still active for soft lockup detection. Patch 2/3 essentially makes watchdog_nmi_enable() behave in the same way as if -ENOENT would have been returned by perf_event_create_kernel_counter(). This is then reported via a console message. NMI watchdog: disabled (cpu0): hardware events not enabled It's hard say what _is_ 'the right value' (because lockup detection is then enabled 'partially'), regardless of whether patch 2/3 is applied or not. Regards, Uli -- 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/