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 Cc: Ingo Molnar Cc: Thomas Gleixner Cc: john stultz Cc: Zachary Amsden Cc: James Morris Cc: Dan Hecht Cc: Paul Mackerras Cc: Martin Schwidefsky Cc: Prarit Bhargava Cc: Chris Lalancette Cc: Rick Lindsley --- kernel/softlockup.c | 28 +++++++++++++++++++--------- 1 file changed, 19 insertions(+), 9 deletions(-) =================================================================== --- a/kernel/softlockup.c +++ b/kernel/softlockup.c @@ -17,8 +17,8 @@ static DEFINE_SPINLOCK(print_lock); -static DEFINE_PER_CPU(unsigned long, touch_timestamp); -static DEFINE_PER_CPU(unsigned long, print_timestamp); +static DEFINE_PER_CPU(unsigned long long, touch_timestamp); +static DEFINE_PER_CPU(unsigned long long, print_timestamp); static DEFINE_PER_CPU(struct task_struct *, watchdog_task); static int did_panic = 0; @@ -37,7 +37,7 @@ static struct notifier_block panic_block void touch_softlockup_watchdog(void) { - __raw_get_cpu_var(touch_timestamp) = jiffies; + __raw_get_cpu_var(touch_timestamp) = sched_clock(); } EXPORT_SYMBOL(touch_softlockup_watchdog); @@ -48,10 +48,15 @@ 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 long touch_timestamp = per_cpu(touch_timestamp, this_cpu); + unsigned long 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; + + /* report at most once a second */ + if (per_cpu(print_timestamp, this_cpu) < (touch_timestamp + NSEC_PER_SEC) || did_panic || !per_cpu(watchdog_task, this_cpu)) return; @@ -62,12 +67,14 @@ void softlockup_tick(void) return; } + now = sched_clock(); + /* Wake up the high-prio watchdog task every second: */ - if (time_after(jiffies, touch_timestamp + HZ)) + if (now > (touch_timestamp + NSEC_PER_SEC)) 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 + 10ull*NSEC_PER_SEC)) { per_cpu(print_timestamp, this_cpu) = touch_timestamp; spin_lock(&print_lock); @@ -87,6 +94,9 @@ 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 +130,7 @@ 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; -- - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/