RE: IRQ affinity enforced only after first interrupt.

From: Yevgeny Petrilin
Date: Tue Mar 27 2012 - 05:39:43 EST

> > >
> > > The architecture specific code will determine whether the IRQ could be migrated
> > > in process context. For example, the IRQ_MOVE_PCNTXT flag will be set on x86
> > > systems if interrupt remapping is enabled.
> >
> > Actually I am encountering this issue with x86, and see different
> > behavior with different HW devices (NICs). On same machine I have
> > one device that responds immediately to affinity changes while the
> > other one changes the affinity only after first interrupt.
> That simply depends on the underlying hardware. On certain hardware we
> can change the affinity only in hard interrupt context, that means
> right when a interrupt of that device is delivered.
> On the other devices we can change it right away and the corresponding
> interrupt chips set IRQ_MOVE_PCNTXT to indicate that.
> There is nothing we can do about this. It's dictated by hardware.

Thanks for the explanation,
Which capabilities of the HW show whether IRQ_MOVE_PCNTXT can be set or not?
Is it done by reading configuration from PCI?

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