Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757680Ab3ETSOb (ORCPT ); Mon, 20 May 2013 14:14:31 -0400 Received: from mail-we0-f179.google.com ([74.125.82.179]:43744 "EHLO mail-we0-f179.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755618Ab3ETSOa (ORCPT ); Mon, 20 May 2013 14:14:30 -0400 Date: Mon, 20 May 2013 20:14:26 +0200 From: Frederic Weisbecker To: Don Zickus Cc: LKML , Steven Rostedt , "Paul E. McKenney" , Ingo Molnar , Andrew Morton , Thomas Gleixner , Peter Zijlstra , Li Zhong Subject: Re: [PATCH 3/8] watchdog: Boot-disable by default on full dynticks Message-ID: <20130520181424.GA22846@somewhere> References: <1369065716-22801-1-git-send-email-fweisbec@gmail.com> <1369065716-22801-4-git-send-email-fweisbec@gmail.com> <20130520175229.GI133453@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20130520175229.GI133453@redhat.com> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1321 Lines: 28 On Mon, May 20, 2013 at 01:52:29PM -0400, Don Zickus wrote: > On Mon, May 20, 2013 at 06:01:51PM +0200, Frederic Weisbecker wrote: > > When the watchdog runs, it prevents the full dynticks > > CPUs from stopping their tick because the hard lockup > > detector uses perf events internally, which in turn > > rely on the periodic tick. > > > > Since this is a rather confusing behaviour that is not > > easy to track down and identify for those who want to > > test CONFIG_NO_HZ_FULL, let's default disable the > > watchdog on boot time when full dynticks is enabled. > > > > The user can still enable it later on runtime using > > proc or sysctl. > > I thought Peter committed a patch to perf so that this isn't needed any > more? There is the patchset that converts perf_event_task_tick() to an hrtimer. But I'm not sure it covers everything. Also this will be for the next merge window. And in the end this moves the problem elsewhere: we still have timer interrupts, they just come as specific hrtimers, although may be less often, I haven't looked yet at the patchset. -- 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/