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

[Lan Tianyu <tianyu.lan@xxxxxxxxx>]

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.

> 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.


> Jan


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