Re: [Xen-devel] debug keys (namely '*') vs. NMI watchdog (and so

To:	Jan Beulich <JBeulich@xxxxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxx>
Subject:	Re: [Xen-devel] debug keys (namely '*') vs. NMI watchdog (and softirqs)
From:	Keir Fraser <keir@xxxxxxx>
Date:	Tue, 14 Dec 2010 10:01:02 +0000
Cc:
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Thread-topic:	[Xen-devel] debug keys (namely '*') vs. NMI watchdog (and softirqs)
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On 14/12/2010 09:48, "Jan Beulich" <JBeulich@xxxxxxxxxx> wrote:

> Processing particularly of '*' may take many seconds, and thus
> interfere with the NMI watchdog (immediately terminal) as well as
> handling of other softirqs, namely the time related ones (possibly
> getting the system into bad state as we know from past
> experience).
> 
> For the NMI watchdog, adding a Linux-like touch_nmi_watchdog()
> would certainly help, but it would leave the softirq part
> unaddressed. For that, in -unstable it would seem feasible to simply
> sprinkle in calls to process_pending_softirqs() (e.g. between each
> individual handler being called), but it's not immediately clear
> whether the same would also hold for 4.0 and earlier, as tasklets
> (and hence the handling of the non-IRQ key handlers) there get
> processed in a softirq action handler. Would it be correct to have
> yet another flavor of the wrappers around __do_softirq() for this
> purpose, also filtering out TASKLET_SOFTIRQ?

For 4.0.2? Yes, that's probably best. As you say it's not needed for
xen-unstable since tasklets execute in vcpu context there.

 -- Keir



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Re: [Xen-devel] debug keys (namely '*') vs. NMI watchdog (and softirqs)