Re: [Xen-devel] Using debug-key 'o: Dump IOMMU p2m table, locks up machine

[Keir Fraser <keir.xen@xxxxxxxxx>]

On 02/09/2012 03:08, "Santosh Jodh" <Santosh.Jodh@xxxxxxxxxx> wrote:

>>>> It might schedule softirqs but that won't include scheduling or
>>>> running any guest vcpus. The vcpu that happens to be running on that
>>>> cpu at the time the debug dump starts, will be stuck unrunnable until the
>> dump completes.
>>> 
>>> Why does'nt that vCPU get scheduled on some other pCPU? Is there  a
>>> way to yield the CPU from the key handler?
>> 
>> It can't be descheduled from this pCPU without running through the
>> scheduler. You could try running the handler in a tasklet -- a tasklet causes
>> other vCPUs to be descheduled from that pCPU, before it starts running.
>> 
>> So you'd register a keyhandler which does a tasklet_schedule(), and do your
>> logging work in the tasklet handler.
>> 
>> Worth a shot maybe?
> 
> Yes - certainly. Is there a reason why all key handlers should not be
> tasklets?

Some keys you want to print immediately (stack trace), or you are using them
when the system is in a bad way, and deferring the tracing may cause you to
get no tracing at all. There may be a few informational keys, for irqs and
the like, that could be moved to tasklet context though, yes. It's just the
tasklet-in-hypervisor-thread mechanism is newer than the key handlers. ;-)

 -- Keir



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