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From: Don Zickus on 9 Apr 2010 11:10 On Fri, Apr 09, 2010 at 06:56:50PM +0400, Cyrill Gorcunov wrote: > 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. Correct. > > > > > 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 Cheers, Don -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo(a)vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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