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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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