From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754234Ab0C0Xhm (ORCPT ); Sat, 27 Mar 2010 19:37:42 -0400 Received: from rcsinet12.oracle.com ([148.87.113.124]:61759 "EHLO rcsinet12.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754211Ab0C0Xhl (ORCPT ); Sat, 27 Mar 2010 19:37:41 -0400 Date: Sat, 27 Mar 2010 16:36:30 -0700 From: Joel Becker To: Yury Polyanskiy Cc: linux-kernel@vger.kernel.org, Andrew Morton , john stultz , Jan Glauber Subject: Re: [PATCH] hangcheck-timer is broken on x86 Message-ID: <20100327233630.GB1810@mail.oracle.com> Mail-Followup-To: Yury Polyanskiy , linux-kernel@vger.kernel.org, Andrew Morton , john stultz , Jan Glauber References: <20100323233611.6dcbe4f4@penta.localdomain> <20100326214648.GF9984@mail.oracle.com> <20100326180025.052d930f@penta.localdomain> <20100327005710.GA31009@mail.oracle.com> <20100326220259.702859e9@penta.localdomain> <20100327220355.GA1810@mail.oracle.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: X-Burt-Line: Trees are cool. X-Red-Smith: Ninety feet between bases is perhaps as close as man has ever come to perfection. User-Agent: Mutt/1.5.20 (2009-06-14) X-Source-IP: acsmt353.oracle.com [141.146.40.153] X-Auth-Type: Internal IP X-CT-RefId: str=0001.0A090208.4BAE9699.00B9:SCFMA4539814,ss=1,fgs=0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sat, Mar 27, 2010 at 06:51:01PM -0400, Yury Polyanskiy wrote: > >        It's OK to tell hangcheck-timer users that suspend is not > > allowed.  After all, you're running something that you don't want to see > > hang. > > Joel, what I am saying is exactly the opposite: it is totally ok to > suspend-resume with hangcheck-timer (jiffies are stopped and so is > getrawmonotonic() when system suspended). Nope. The point of hangcheck-timer is that it reboots should the system not be running for a certain amountof time. If suspend-resume is allowed, a system can resume after days and think it wasn't more than a second. hangcheck-timer will not know to reboot. > >        Is there a clock in the system that is a true wallclock?  I'm > > guessing, since getrawmonotonic() is get_cycles() based, that it doesn't > > provide accurate time in the face of cpufreq changes.  Is that true? > > Of course, getrawmonotonic accounts for cpufreq changes (see > arch/x86/kernel/tsc.c:time_cpufreq_notifier()). Excellent! That's a definite improvement over raw get_cycles(). Joel -- Life's Little Instruction Book #182 "Be romantic." Joel Becker Principal Software Developer Oracle E-mail: joel.becker@oracle.com Phone: (650) 506-8127