On 11.12.20 00:20, boris.ostrovsky@oracle.com 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.

After some discussion with Thomas on IRC and xen-devel archaeology the
result is: this will be needed especially for systems running on a
single vcpu (e.g. small guests), as the .irq_set_affinity() callback
won't be called in this case when starting the irq.


Juergen