[patch 27/30] xen/events: Only force affinity mask for percpu interrupts

[Thomas Gleixner]

On Thu, Dec 10 2020 at 18:20, boris ostrovsky wrote:
> On 12/10/20 2:26 PM, Thomas Gleixner wrote:
>> All event channel setups bind the interrupt on CPU0 or the target CPU for
>> percpu interrupts and overwrite the affinity mask with the corresponding
>> cpumask. That does not make sense.
>>
>> The XEN implementation of irqchip::irq_set_affinity() already picks a
>> single target CPU out of the affinity mask and the actual target is stored
>> in the effective CPU mask, so destroying the user chosen affinity mask
>> which might contain more than one CPU is wrong.
>>
>> Change the implementation so that the channel is bound to CPU0 at the XEN
>> level and leave the affinity mask alone. At startup of the interrupt
>> affinity will be assigned out of the affinity mask and the XEN binding will
>> be updated. 
>
> If that's the case then I wonder whether we need this call at all and
> instead bind at startup time.

I was wondering about that, but my knowledge about the Xen internal
requirements is pretty limited. The current set at least survived basic
testing by Jürgen.

Thanks,

        tglx