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    SubjectRE: [PATCH v2 1/2] x86: skip migrating IRQF_PER_CPU irq in fixup_irqs
    > From: Konrad Rzeszutek Wilk [mailto:konrad.wilk@oracle.com]
    > Sent: Friday, May 06, 2011 9:58 PM
    >
    > On Fri, May 06, 2011 at 02:43:36PM +0800, Tian, Kevin wrote:
    > > x86: skip migrating IRQF_PER_CPU irq in fixup_irqs
    > >
    > > IRQF_PER_CPU marks a irq binding to a specific cpu, and can never be
    > > moved away from that cpu. So it shouldn't be migrated when fixup irqs
    > > to offline a cpu. Xen pvops guest is one source using IRQF_PER_CPU
    > ^- are called
    > > on a set of virtual interrupts. Previously no error is observed
    > ^^- was
    > Which ones? Can you be more specific here of which type of virtual interrupts?
    > spinlock? timer?

    all of them: spinlock, timer, resched, callfunc, ...

    > > because Xen event chip silently fails the set_affinity ops, and
    > > logically IRQF_PER_CPU should be recognized here.
    >
    > OK, so what if the set_affinity ops was implemented?

    it was implemented: (drivers/xen/event.c, rebind_irq_to_cpu)
    /*
    * If this fails, it usually just indicates that we're dealing with a
    * virq or IPI channel, which don't actually need to be rebound. Ignore
    * it, but don't do the xenlinux-level rebind in that case.
    */
    if (HYPERVISOR_event_channel_op(EVTCHNOP_bind_vcpu, &bind_vcpu) >= 0)
    bind_evtchn_to_cpu(evtchn, tcpu);
    Hypervisor doesn't allow to change affinity for virq and ipi.

    Thanks,
    Kevin

    > >
    > > Signed-off-by: Fengzhe Zhang <fengzhe.zhang@intel.com>
    > > Signed-off-by: Kevin Tian <kevin.tian@intel.com>
    > > CC: Thomas Gleixner <tglx@linutronix.de>
    > > CC: Ingo Molnar <mingo@redhat.com>
    > > CC: H. Peter Anvin <hpa@zytor.com>
    > > CC: Ian Campbell <Ian.Campbell@citrix.com>
    > > CC: Jan Beulich <JBeulich@novell.com>
    > >
    > > --- linux-2.6.39-rc6.orig/arch/x86/kernel/irq.c 2011-05-04
    > 10:59:13.000000000 +0800
    > > +++ linux-2.6.39-rc6/arch/x86/kernel/irq.c 2011-05-06 09:20:25.563963000
    > +0800
    > > @@ -249,7 +250,7 @@ void fixup_irqs(void)
    > >
    > > data = irq_desc_get_irq_data(desc);
    > > affinity = data->affinity;
    > > - if (!irq_has_action(irq) ||
    > > + if (!irq_has_action(irq) || irqd_is_per_cpu(data) ||
    > > cpumask_subset(affinity, cpu_online_mask)) {
    > > raw_spin_unlock(&desc->lock);
    > > continue;
    > > --
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