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

[Jürgen Groß <jgross@xxxxxxxx>]

On 11.12.20 00:20, boris.ostrovsky@xxxxxxxxxx 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

Attachment: OpenPGP_0xB0DE9DD628BF132F.asc
Description: application/pgp-keys

Attachment: OpenPGP_signature
Description: OpenPGP digital signature