RE: [Xen-devel] [PATCH] Fix softlockup issue after vcpu hotplug

["Tian, Kevin" <kevin.tian@xxxxxxxxx>]

>From: Keir Fraser [mailto:Keir.Fraser@xxxxxxxxxxxx]
>Sent: 2007年1月30日 20:59
>On 30/1/07 12:11 pm, "Tian, Kevin" <kevin.tian@xxxxxxxxx> wrote:
>
>>> Presumably softlockup threads are killed and re-created when
>VCPUs
>>> are
>>> offlined and onlined. Perhaps the re-creation is taking a long time?
>But
>>
>> That should not be the case, since the softlockup warning continues
>> to jump out after cpu is brought online.
>
>You are confusing the two parts of the softlockup mechanism. The thread
>is
>responsible only for periodically touching the watchdog. The warning
>mechanism is driven off the timer interrupt handler. So it is entirely
>possible for warnings to appear when the thread does not exist (in fact, if
>the thread does not exist then we *expect* warnings to appear!).
>
> -- Keir

I added a debug print inside the warning by:
        printk(KERN_ERR "BUG: drift by 0x%lx\n", 
                        jiffies - touch_timestamp);

This drift doesn't increment monotonically. Most time it is about 1s 
(an interesting fact!), and seldom dozen of seconds. But anyway, it 
indicates that watchdog thread is still scheduled. :-)

Thanks,
Kevin

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