Ignore stolen time in the softlockup watchdog
The softlockup watchdog is currently a nuisance in a virtual machine, since the whole system could have the CPU stolen from it for a long period of time. While it would be unlikely for a guest domain to be denied timer interrupts for over 10s, it could happen and any softlockup message would be completely spurious. Earlier I proposed that sched_clock() return time in unstolen nanoseconds, which is how Xen and VMI currently implement it. If the softlockup watchdog uses sched_clock() to measure time, it would automatically ignore stolen time, and therefore only report when the guest itself locked up. When running native, sched_clock() returns real-time nanoseconds, so the behaviour would be unchanged. Note that sched_clock() used this way is inherently per-cpu, so this patch makes sure that the per-processor watchdog thread initialized its own timestamp. Signed-off-by: Jeremy Fitzhardinge <jeremy@xensource.com> Cc: Ingo Molnar <mingo@elte.hu> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: john stultz <johnstul@us.ibm.com> Cc: Zachary Amsden <zach@vmware.com> Cc: James Morris <jmorris@namei.org> Cc: Dan Hecht <dhecht@vmware.com> Cc: Paul Mackerras <paulus@samba.org> Cc: Martin Schwidefsky <schwidefsky@de.ibm.com> Cc: Prarit Bhargava <prarit@redhat.com> Cc: Chris Lalancette <clalance@redhat.com> Cc: Rick Lindsley <ricklind@us.ibm.com> Cc: Eric Dumazet <dada1@cosmosbay.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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1 changed files with 29 additions and 6 deletions
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@ -34,9 +34,19 @@ static struct notifier_block panic_block = {
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.notifier_call = softlock_panic,
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.notifier_call = softlock_panic,
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};
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};
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/*
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* Returns seconds, approximately. We don't need nanosecond
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* resolution, and we don't need to waste time with a big divide when
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* 2^30ns == 1.074s.
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*/
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static unsigned long get_timestamp(void)
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{
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return sched_clock() >> 30; /* 2^30 ~= 10^9 */
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}
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void touch_softlockup_watchdog(void)
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void touch_softlockup_watchdog(void)
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{
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{
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__raw_get_cpu_var(touch_timestamp) = jiffies;
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__raw_get_cpu_var(touch_timestamp) = get_timestamp();
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}
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}
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EXPORT_SYMBOL(touch_softlockup_watchdog);
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EXPORT_SYMBOL(touch_softlockup_watchdog);
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@ -48,9 +58,17 @@ void softlockup_tick(void)
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{
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{
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int this_cpu = smp_processor_id();
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int this_cpu = smp_processor_id();
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unsigned long touch_timestamp = per_cpu(touch_timestamp, this_cpu);
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unsigned long touch_timestamp = per_cpu(touch_timestamp, this_cpu);
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unsigned long print_timestamp;
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unsigned long now;
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/* prevent double reports: */
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/* watchdog task hasn't updated timestamp yet */
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if (per_cpu(print_timestamp, this_cpu) == touch_timestamp ||
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if (touch_timestamp == 0)
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return;
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print_timestamp = per_cpu(print_timestamp, this_cpu);
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/* report at most once a second */
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if (print_timestamp < (touch_timestamp + 1) ||
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did_panic ||
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did_panic ||
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!per_cpu(watchdog_task, this_cpu))
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!per_cpu(watchdog_task, this_cpu))
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return;
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return;
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@ -61,12 +79,14 @@ void softlockup_tick(void)
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return;
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return;
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}
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}
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now = get_timestamp();
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/* Wake up the high-prio watchdog task every second: */
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/* Wake up the high-prio watchdog task every second: */
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if (time_after(jiffies, touch_timestamp + HZ))
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if (now > (touch_timestamp + 1))
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wake_up_process(per_cpu(watchdog_task, this_cpu));
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wake_up_process(per_cpu(watchdog_task, this_cpu));
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/* Warn about unreasonable 10+ seconds delays: */
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/* Warn about unreasonable 10+ seconds delays: */
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if (time_after(jiffies, touch_timestamp + 10*HZ)) {
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if (now > (touch_timestamp + 10)) {
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per_cpu(print_timestamp, this_cpu) = touch_timestamp;
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per_cpu(print_timestamp, this_cpu) = touch_timestamp;
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spin_lock(&print_lock);
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spin_lock(&print_lock);
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@ -87,6 +107,9 @@ static int watchdog(void * __bind_cpu)
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sched_setscheduler(current, SCHED_FIFO, ¶m);
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sched_setscheduler(current, SCHED_FIFO, ¶m);
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current->flags |= PF_NOFREEZE;
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current->flags |= PF_NOFREEZE;
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/* initialize timestamp */
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touch_softlockup_watchdog();
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/*
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/*
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* Run briefly once per second to reset the softlockup timestamp.
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* Run briefly once per second to reset the softlockup timestamp.
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* If this gets delayed for more than 10 seconds then the
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* If this gets delayed for more than 10 seconds then the
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@ -118,7 +141,7 @@ cpu_callback(struct notifier_block *nfb, unsigned long action, void *hcpu)
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printk("watchdog for %i failed\n", hotcpu);
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printk("watchdog for %i failed\n", hotcpu);
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return NOTIFY_BAD;
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return NOTIFY_BAD;
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}
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}
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per_cpu(touch_timestamp, hotcpu) = jiffies;
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per_cpu(touch_timestamp, hotcpu) = 0;
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per_cpu(watchdog_task, hotcpu) = p;
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per_cpu(watchdog_task, hotcpu) = p;
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kthread_bind(p, hotcpu);
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kthread_bind(p, hotcpu);
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break;
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break;
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