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Ignore stolen time in the softlockup watchdog

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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>
This commit is contained in:
Jeremy Fitzhardinge 2007-05-08 00:28:02 -07:00 committed by Linus Torvalds
parent 8524070b79
commit 966812dc98
1 changed files with 29 additions and 6 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

35
kernel/softlockup.c
View File

@ -34,9 +34,19 @@ static struct notifier_block panic_block = {
.notifier_call = softlock_panic,
};
/*
* Returns seconds, approximately. We don't need nanosecond
* resolution, and we don't need to waste time with a big divide when
* 2^30ns == 1.074s.
*/
static unsigned long get_timestamp(void)
{
return sched_clock() >> 30; /* 2^30 ~= 10^9 */
}
void touch_softlockup_watchdog(void)
{
__raw_get_cpu_var(touch_timestamp) = jiffies;
__raw_get_cpu_var(touch_timestamp) = get_timestamp();
}
EXPORT_SYMBOL(touch_softlockup_watchdog);
@ -48,9 +58,17 @@ void softlockup_tick(void)
{
int this_cpu = smp_processor_id();
unsigned long touch_timestamp = per_cpu(touch_timestamp, this_cpu);
unsigned long print_timestamp;
unsigned long now;
/* prevent double reports: */
if (per_cpu(print_timestamp, this_cpu) == touch_timestamp ||
/* watchdog task hasn't updated timestamp yet */
if (touch_timestamp == 0)
return;
print_timestamp = per_cpu(print_timestamp, this_cpu);
/* report at most once a second */
if (print_timestamp < (touch_timestamp + 1) ||
did_panic ||
!per_cpu(watchdog_task, this_cpu))
return;
@ -61,12 +79,14 @@ void softlockup_tick(void)
return;
}
now = get_timestamp();
/* Wake up the high-prio watchdog task every second: */
if (time_after(jiffies, touch_timestamp + HZ))
if (now > (touch_timestamp + 1))
wake_up_process(per_cpu(watchdog_task, this_cpu));
/* Warn about unreasonable 10+ seconds delays: */
if (time_after(jiffies, touch_timestamp + 10*HZ)) {
if (now > (touch_timestamp + 10)) {
per_cpu(print_timestamp, this_cpu) = touch_timestamp;
spin_lock(&print_lock);
@ -87,6 +107,9 @@ static int watchdog(void * __bind_cpu)
sched_setscheduler(current, SCHED_FIFO, &param);
current->flags |= PF_NOFREEZE;
/* initialize timestamp */
touch_softlockup_watchdog();
/*
* Run briefly once per second to reset the softlockup timestamp.
* If this gets delayed for more than 10 seconds then the
@ -118,7 +141,7 @@ cpu_callback(struct notifier_block *nfb, unsigned long action, void *hcpu)
printk("watchdog for %i failed\n", hotcpu);
return NOTIFY_BAD;
}
per_cpu(touch_timestamp, hotcpu) = jiffies;
per_cpu(touch_timestamp, hotcpu) = 0;
per_cpu(watchdog_task, hotcpu) = p;
kthread_bind(p, hotcpu);
break;