On 06/17/2011 01:03 PM, Jan Kiszka wrote:
> On 2011-06-17 12:55, Gilles Chanteperdrix wrote:
>> On 06/17/2011 11:26 AM, Jan Kiszka wrote:
>>> Our current interrupt handlers assume that they leave over the same task
>>> and CPU they entered. But CONFIG_XENO_HW_UNLOCKED_SWITCH and commit
>>> f6af9b831c broke this assumption: xnpod_schedule invoked from the
>>> handler tail can now actually trigger a domain migration
>>
>> What unlocked context swith introduce from my point of view is simply
>> sections where interrupt happen which do not reschedule.
>>
>> f6af9b831c introduce a rescheduling point, but does not change what
>> happens during the interrupt handler either.
>>
>> So, I do not really understand this commit message. Either we can assume
>> that interrupt handlers migrate tasks or not, but this does not seem to
>> have anything to do with unlocked context switches or commit f6af9b831c.
> 
> It has: Task is about to relax, re-enables interrupts in
> xnpod_resume_thread, IRQ hits, handler is entered over the relaxing RT
> task, xnpod_schedule in its tail performs the switch to root, which then
> continues to relaxed task, IRQ tail resumes over a different task, on
> SMP potentially also on a different CPU. I can send you a the trace if
> you want to have a closer look.

Ok. Got it. But what has this to do with unlocked context switches ?

-- 
                                                                Gilles.

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