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 <[EMAIL PROTECTED]>
Cc: Ingo Molnar <[EMAIL PROTECTED]>
Cc: Thomas Gleixner <[EMAIL PROTECTED]>
Cc: john stultz <[EMAIL PROTECTED]>
Cc: Zachary Amsden <[EMAIL PROTECTED]>
Cc: James Morris <[EMAIL PROTECTED]>
Cc: Dan Hecht <[EMAIL PROTECTED]>
Cc: Paul Mackerras <[EMAIL PROTECTED]>
Cc: Martin Schwidefsky <[EMAIL PROTECTED]>
Cc: Prarit Bhargava <[EMAIL PROTECTED]>
Cc: Chris Lalancette <[EMAIL PROTECTED]>
Cc: Rick Lindsley <[EMAIL PROTECTED]>
Cc: Eric Dumazet <[EMAIL PROTECTED]>
---
kernel/softlockup.c | 37 ++++++++++++++++++++++++++++++-------
1 file changed, 30 insertions(+), 7 deletions(-)
===================================================================
--- a/kernel/softlockup.c
+++ b/kernel/softlockup.c
@@ -35,9 +35,19 @@ 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);
@@ -48,10 +58,18 @@ void softlockup_tick(void)
void softlockup_tick(void)
{
int this_cpu = smp_processor_id();
- unsigned long touch_timestamp = per_cpu(touch_timestamp, this_cpu);
+ unsigned long touch_timestamp = __get_cpu_var(touch_timestamp);
+ 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 = __get_cpu_var(print_timestamp);
+
+ /* report at most once a second */
+ if (print_timestamp < (touch_timestamp + 1) ||
did_panic ||
!per_cpu(watchdog_task, this_cpu))
return;
@@ -62,12 +80,14 @@ 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, ¶m);
current->flags |= PF_NOFREEZE;
+
+ /* initialize timestamp */
+ touch_softlockup_watchdog();
/*
* Run briefly once per second to reset the softlockup timestamp.
@@ -120,7 +143,7 @@ cpu_callback(struct notifier_block *nfb,
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;
--
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