Re: [Xen-devel] [PATCH] Xen/timer: Disable watchdog during dumping timer queues

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 22.09.16 at 16:18, <tianyu.lan@xxxxxxxxx> wrote:
> On 9/21/2016 5:25 PM, Jan Beulich wrote:
>>>>> On 21.09.16 at 03:54, <tianyu.lan@xxxxxxxxx> wrote:
>>> On 2016年09月20日 23:36, Jan Beulich wrote:
>>>>> The precondition of process_pending_softirq() working in the debug key
>>>>>> handler is that timer interrupt arrives on time and nmi_timer_fn() can
>>>>>> run to update nmi_timer_ticks before watchdog timeout.
>>>> Precondition?
>>>
>>> Process_pending_softirq() in debug key handler is mainly to deal with
>>> timer softirq to update nmi_timer_ticks in order to avoid NMI watchdog.
>>> If there is no timer interrupt arriving for long time,
>>> process_pending_softirq() here is meaningless and NMI watchdog still
>>> will be timeout.
>>
>> Oh, right. Still I continue to be unconvinced that disabling the
>> watchdog is the right answer (not running timers for a long time
>> has other undesirable consequence), or if it is, then it being
>> needed in only this one key handler. So perhaps you should
>> really consider submitting your generic key handler adjustment
>> as an alternative.
> 
> Disable watchdog is common solution for such kind of issues in current
> codes and so I chose it. I also proposed another solution in previous
> mail that run keyhandler always in a tasklet and insert
> process_pending_softirq() in the keyhandler.

Yes, that's the patch I've been referring to in my previous answer.

>> But please also answer the earlier question, which you did strip
>> from your reply:
>>
>>> Which btw raises another question: Why are you in polling mode in
>>> the first place? Do you have a UART without working interrupt?
> 
> I found there was no interrupt with Xen ns16550 dirver while
> linux kernel's serial driver can receive interrupt.

And do you know the reason? Is it perhaps a PCI plug in card, and
you don't specify the IRQ on the command line? Or the kernel
doesn't provide the necessary information (from ACPI) for Xen to
set up that IRQ?

Jan

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