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Re: [Xen-devel] IRQ SMP affinity problems in domU with vcpus > 4 on HP ProLiant G6 with dual Xeon 5540 (Nehalem)

On Fri, 2009-10-16 at 15:32 +0800, Zhang, Xiantao wrote:
> According to the description, the issue should be caused by lost EOI write
> for the MSI interrupt and leads to permanent interrupt mask. There should
> be a race between guest setting new vector and  EOIs old vector for the
> interrupt.  Once guest sets new vector before it EOIs the old vector,
> hypervisor can't find the pirq which corresponds old vector(has changed
> to new vector) , so also can't EOI the old vector forever in hardware
> level. Since the corresponding vector in real processor can't be EOIed,
> so system may lose all interrupts and result the reported issues ultimately.

> But I remembered there should be a timer to handle this case
> through a forcible EOI write to the real processor after timeout,
> but seems it doesn't function in the expected way.

The EOI timer is supposed to deal with the irq sharing problem,
since MSI doesn't share, this timer will not be started in the
case of MSI.

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