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SubjectRe: [patch 11/26] x64, x2apic/intr-remap: generic irq migration support from process context
On Thu, Jul 10, 2008 at 04:08:03PM -0700, Eric W. Biederman wrote:
> Suresh Siddha <suresh.b.siddha@intel.com> writes:
>
> > Generic infrastructure for migrating the irq from the process context in the
> > presence of CONFIG_GENERIC_PENDING_IRQ.
> >
> > This will be used later for migrating irq in the presence of
> > interrupt-remapping.
>
> Why the API difference between IRQ_MOVE_PCNTXT set affinity handlers and
> !CONFIG_GENERIC_PENDING_IRQ handlers?

You are referring to desc->lock portion?

Two reasons:

a. Other code in CONFIG_GENERIC_PENDING_IRQ, assuming that desc->lock is held
while calling set_affinity. like fixup_irqs(). Just wanted to be same
across the board.

b. for level triggered, we still touch irq_desc and set IRQ_MOVE_PENDING,
when we fail to move the irq (if there is already some level triggered
interrupt happening in parallel). while, we can acquire the lock inside
the set_affinity, I thought this simplifies things.

>
>
> > #ifdef CONFIG_GENERIC_PENDING_IRQ
> > - set_pending_irq(irq, cpumask);
> > + if (desc->status & IRQ_MOVE_PCNTXT) {
> > + unsigned long flags;
> > +
> > + spin_lock_irqsave(&desc->lock, flags);
> > + desc->chip->set_affinity(irq, cpumask);
> > + spin_unlock_irqrestore(&desc->lock, flags);
> > + } else
> > + set_pending_irq(irq, cpumask);
> > #else
> > desc->affinity = cpumask;
> > desc->chip->set_affinity(irq, cpumask);
> >
> > --

thanks,
suresh


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