Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S966369AbaLMJ5u (ORCPT ); Sat, 13 Dec 2014 04:57:50 -0500 Received: from mail-wi0-f169.google.com ([209.85.212.169]:60376 "EHLO mail-wi0-f169.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S966327AbaLMJ5r (ORCPT ); Sat, 13 Dec 2014 04:57:47 -0500 Message-ID: <1418464662.4916.28.camel@marge.simpson.net> Subject: Re: frequent lockups in 3.18rc4 From: Mike Galbraith To: Ingo Molnar Cc: Linus Torvalds , Peter Zijlstra , Chris Mason , =?ISO-8859-1?Q?D=E2niel?= Fraga , Dave Jones , Sasha Levin , "Paul E. McKenney" , Linux Kernel Mailing List Date: Sat, 13 Dec 2014 10:57:42 +0100 In-Reply-To: <20141213081140.GF32572@gmail.com> References: <547b8a45.6e608c0a.20f9.1002@mx.google.com> <547bbe36.48548c0a.105c.779c@mx.google.com> <20141201191431.GA17385@linux.vnet.ibm.com> <547ccf74.a5198c0a.25de.26d9@mx.google.com> <20141201230339.GA20487@ret.masoncoding.com> <1417529606.3924.26.camel@maggy.simpson.net> <1417542432.3924.39.camel@maggy.simpson.net> <20141213081140.GF32572@gmail.com> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.2.3 Content-Transfer-Encoding: 7bit Mime-Version: 1.0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sat, 2014-12-13 at 09:11 +0100, Ingo Molnar wrote: > * Mike Galbraith wrote: > > > On Tue, 2014-12-02 at 08:33 -0800, Linus Torvalds wrote: > > > > > Looking again at that patch (the commit message still doesn't strike > > > me as wonderfully explanatory :^) makes me worry, though. > > > > > > Is that > > > > > > if (rq->skip_clock_update-- > 0) > > > return; > > > > > > really right? If skip_clock_update was zero (normal), it now gets set > > > to -1, which has its own specific meaning (see "force clock update" > > > comment in kernel/sched/rt.c). Is that intentional? That seems insane. > > > > Yeah, it was intentional. Least lines. > > > > > Or should it be > > > > > > if (rq->skip_clock_update > 0) { > > > rq->skip_clock_update = 0; > > > return; > > > } > > > > > > or what? Maybe there was a reason the patch never got applied even to -tip. > > > > Peterz was looking at corner case proofing the thing. Saving those > > cycles has been entirely too annoying. > > > > https://lkml.org/lkml/2014/4/8/295 > > Hm, so that discussion died with: > > https://lkml.org/lkml/2014/4/8/343 > > Did you ever get around to trying Peter's patch? I couldn't plug it into the production -ENOBOOT IO beasts from hell, but did run it on my little desktop a bit. > But ... I've yet to see rq_clock problems cause actual lockups. > That's the main problem we have with its (un)robustness and why > Peter created that rq_clock debug facility: bugs there cause > latencies but no easily actionable symptoms, which are much > harder to debug. If watchdog gets credit for zillion disk detection time, it can end up throttled for what is effectively forever. -Mike -- 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/