From mboxrd@z Thu Jan 1 00:00:00 1970 From: Prarit Bhargava Subject: Re: [patch 1/2] Ignore stolen time in the softlockup watchdog Date: Tue, 27 Mar 2007 13:20:52 -0400 Message-ID: <46095274.7050502@redhat.com> References: <20070327053816.881735237@goop.org> <20070327054106.664262413@goop.org> <46092C9B.4030700@redhat.com> <46094861.7080400@goop.org> <46094C02.9050702@redhat.com> <46095006.2000306@xensource.com> Mime-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Return-path: In-Reply-To: <46095006.2000306@xensource.com> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: virtualization-bounces@lists.linux-foundation.org Errors-To: virtualization-bounces@lists.linux-foundation.org To: Jeremy Fitzhardinge Cc: virtualization@lists.osdl.org, Rick Lindsley , Andrew Morton , Thomas Gleixner , Martin Schwidefsky , john stultz , Ingo Molnar , Linux Kernel , Paul Mackerras List-Id: virtualization@lists.linuxfoundation.org Jeremy Fitzhardinge wrote: > Prarit Bhargava wrote: > = >> Jeremy Fitzhardinge wrote: >> = >> = >>> Prarit Bhargava wrote: >>> = >>> = >>> = >>>> I'd like to see this patch implement/fix touch_cpu_softlockup_watchdog >>>> and touch_softlockup_watchdog to mimic touch_nmi_watchdog's behaviour. >>>> = >>>> = >>>> = >>> Why? Is that more correct? It seems to me that you're interested in >>> whether a specific CPU has gone and locked up. If touching the watchdog >>> = >>> makes it update all CPU timestamps, then you'll hide the fact that other >>> CPUs have locked up, won't it? >>> >>> = >>> = >>> = >> In case of misuse, yes. But there are cases where we know that all CPUs = >> will have softlockup issues, such as when doing a "big" sysrq-t dump. = >> When doing the sysrq-t we take the tasklist_lock which prevents all = >> other CPUs from scheduling -- this leads to bogus softlockup messages, = >> so we need to reset everyone's watchdog just before releasing the = >> tasklist_lock. >> >> Another question -- are you going to expose disable/enable_watchdog to = >> other subsystems? Or are you going to expose touch_softlockup_watchdog? >> = > > Well, it depends on who turns up. = > > My first thought is to export both the global enable/disable interfaces > and touch_softlockup_watchdog. But on second thoughts maybe > touch_softlockup_watchdog is completely redundant, since you'd only do > = IMO, if you export enable/disable you should drop touch_softlockup_watchdog. > it if you're holding off timer interrupts, but the lockup only gets > reported if timer interrupts are enabled (in other words, the best it > can tell you is "you locked up for a while there", which isn't terribly > useful). = I like to think of the softlockup watchdog letting me know that a cpu = hasn't scheduled in a long time. > So perhaps this can just be dropped. I haven't looked at the > users to see what they're really trying to achieve. > = I've looked through much of that code for my previous patch ;) AFAICT the uses appear to be cases where we _know_ that we've gone away = for a while and need to reset the timer. But there were some exceptions: touch_nmi_watchdog erroneously calls = touch_softlockup_watchdog. In fact, touch_nmi_watchdog is trying to = touch all cpus softlockup watchdogs, not just one. IIRC, There was an extra call to touch_softlockup_watchdog which wasn't = necessary IIRC... Look at my previous patch where I replaced touch_softlockup_watchdog = with touch_cpu_softlockup_watchdog ... > The enable/disable interfaces are more generally useful in that you can > say "I *know* I'm going to go away for a while, so don't bother > reporting it". > > J > =