From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1761865Ab2COMmr (ORCPT ); Thu, 15 Mar 2012 08:42:47 -0400 Received: from mx2.mail.elte.hu ([157.181.151.9]:44924 "EHLO mx2.mail.elte.hu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753570Ab2COMmq (ORCPT ); Thu, 15 Mar 2012 08:42:46 -0400 Date: Thu, 15 Mar 2012 13:42:29 +0100 From: Ingo Molnar To: Peter Zijlstra Cc: Mandeep Singh Baines , Andrew Morton , Don Zickus , LKML , Michal Hocko Subject: Re: [PATCH] watchdog: Make sure the watchdog thread gets CPU on loaded system Message-ID: <20120315124228.GA5318@elte.hu> References: <1331757525-5755-1-git-send-email-dzickus@redhat.com> <20120314161906.e53359d3.akpm@linux-foundation.org> <20120315014511.GT27051@google.com> <1331809239.18960.168.camel@twins> <1331809597.18960.171.camel@twins> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1331809597.18960.171.camel@twins> User-Agent: Mutt/1.5.21 (2010-09-15) 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=3.3.1 -2.0 BAYES_00 BODY: Bayes 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 * Peter Zijlstra wrote: > On Thu, 2012-03-15 at 12:00 +0100, Peter Zijlstra wrote: > > On Wed, 2012-03-14 at 18:45 -0700, Mandeep Singh Baines wrote: > > > You could make MAX_RT_PRIO greater than MAX_USER_RT_PRIO but that > > > might > > > have some impact on real-time applications. A simple one-line patch: > > > > > > - #define MAX_RT_PRIO MAX_USER_RT_PRIO > > > + #define MAX_RT_PRIO (MAX_USER_RT_PRIO + 1) > > > > > > would prevent user-space from causing a false lockup detection. > > > > We're so not going to muck with the fifo priorities just for this stupid > > soft watchdog,.. I already hate that I can't disable the piece of crap, > > making it more involved is just really not going to happen. > > And before people start to whinge about that, all the soft > watchdog issues I've seen fly by the past year or so all were > bugs in the watchdog itself, I can't actually remember it > flagging a real problem. Its efficiency always depended on which area I was working on. For syscall level stuff it helped me numerous times. > The NMI watchdog otoh works like a charm for me and regularly > helps out when I done stupid. Sure, you are mostly working on perf events, the scheduler and related core kernel areas so when you are stupid you get a hard lockup or worse, quickly. Not much room for soft lockups. So it's more of a case of selection bias, me thinks. So unless there's concensus to remove everything but the hard lockup detection facilities, lets solve the technical problem at hand, ok? Thanks, Ingo