RE: [Xen-devel] Re: event delay issue on SMP machine when xen0 is SMP enabled

["Li, Xin B" <xin.b.li@xxxxxxxxx>]

>>> BTW, why vcpu other than vcpu0 won't handle event by default?
>>
>> We could allow any vcpu to process any pending 
>notifications. It would 
>> mean vcpus outside an irq's affinity set could end up processing an 
>> interrupt and I'm not sure if that's a good thing. It would actually 
>> slightly simplify evtchn.c though (no need to apply a 
>per-cpu mask to 
>> the event-channel port array).
>
>You always remember a good reason not to do something after 
>sending the 
>email. :-)
>
>IPIs and VIRQs must be processed by their home vcpu. Hence we do need 
>to limit evtchn processing to the current bound vcpu, and that leads 
>(currently) to the problem you see.
>
>So I think the right fix is just to fix unmask_evtchn(). Maybe 
>you guys 
>want to send a patch to move it into evtchn.c and fix it to send to 
>cpu_from_evtchn(evtchn)?
>

Since evtchn code is critical to xen, we are very careful when finding
any possible fixes :-)
Why not turn on cpu_evtchn_mask by default, and when calling
bind_evtchn_to_cpu, we turn off it on other cpus.

Thanks
-Xin

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