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    SubjectRe: [watchdog] combine nmi_watchdog and softlockup
    On Tue, Apr 06, 2010 at 07:31:15PM +0400, Cyrill Gorcunov wrote:
    > On Tue, Apr 06, 2010 at 04:13:30PM +0200, Frederic Weisbecker wrote:
    > [...]
    > > > +static int watchdog_enable(int cpu)
    > > > +{
    > > > + struct perf_event_attr *wd_attr;
    > > > + struct perf_event *event = per_cpu(watchdog_ev, cpu);
    > > > + struct task_struct *p = per_cpu(softlockup_watchdog, cpu);
    > > > +
    > > > + /* is it already setup and enabled? */
    > > > + if (event && event->state > PERF_EVENT_STATE_OFF)
    > > > + goto out;
    > > > +
    > > > + /* it is setup but not enabled */
    > > > + if (event != NULL)
    > > > + goto out_enable;
    > > > +
    > > > + /* Try to register using hardware perf events first */
    > > > + wd_attr = &wd_hw_attr;
    > > > + wd_attr->sample_period = hw_nmi_get_sample_period();
    > > > + event = perf_event_create_kernel_counter(wd_attr, cpu, -1, watchdog_overflow_callback);
    > > > + if (!IS_ERR(event)) {
    > > > + printk(KERN_INFO "NMI watchdog enabled, takes one hw-pmu counter.\n");
    > > > + goto out_save;
    > > > + }
    > > > +
    > > > + /* hardware doesn't exist or not supported, fallback to software events */
    > > > + printk(KERN_INFO "NMI watchdog: hardware not available, trying software events\n");
    > > > + wd_attr = &wd_sw_attr;
    > > > + wd_attr->sample_period = softlockup_thresh * NSEC_PER_SEC;
    > > > + event = perf_event_create_kernel_counter(wd_attr, cpu, -1, watchdog_overflow_callback);
    > >
    > > 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?


    Yeah but only a part of the hardlockup classes. Those that have interrupt
    enabled.



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