Messages in this thread | | | Date | Fri, 9 Apr 2010 18:56:50 +0400 | From | Cyrill Gorcunov <> | Subject | Re: [watchdog] combine nmi_watchdog and softlockup |
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On Fri, Apr 09, 2010 at 02:00:38AM +0200, Frederic Weisbecker wrote: > On Tue, Apr 06, 2010 at 07:31:15PM +0400, Cyrill Gorcunov wrote: > > > I fear the cpu clock is not going to help you detecting any hard lockups. > > > If you're stuck in an interrupt or an irq disabled loop, your cpu clock is > > > not going to fire. > > > > > > > I guess it's not supposed to. For such cases only nmi irqs may help for which > > the perf events are there (/me need to check if we program apic timer for anything > > like that). But it should help for other deadlocks. Or I miss something? > > > Actually not. What the hardlockup detector does it to check the progression > of irqs. >
yup, i know what nmi-watchdog is doing. I guess you've misunderstood me. I meant that sw-driven detector is not supposed to guard against the cases you're referring to. I don't remember the details but someone proposed to make a fallback to sw-watchdog if there is no ability to use nmi from perf-events (for any reason) which eventually being implemented in Don's patch. And there will be a message that watchdog has been switched to sw-driven scaffold. So user will (or should) see this message and mark it I believe. This sw-watchdog is like "ok, we've been trying our best but there is a problem and the only solution we could offer -- is to use sw-watchdog". That is how I understand the reason for sw-watchdog there.
> > So it detects true hardlockups: stuck in an irq disabled section. > If you don't have NMI to detect that (here this made by hardware clock based > on cpu cycles overflows), then you're screwed. The hardlockup detector is > useless with a maskable irq based clock. > -- Cyrill
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