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SubjectRe: [PATCH] perf, nmi: fix unknown NMI warning
On Fri, Feb 14, 2014 at 04:44:08PM -0800, Andi Kleen wrote:
>
> Make intel_pmu_handle_irq() take the full exit path when returning early.

This reminds me of the late-ack stuff;

The way I understand interrupts to work is that when you raise the
interrupt it gets latched, when you ACK you drop the latch. Then when it
gets re-raised while its still in progress, it gets latched again and
the irq-enable at the end of the running handler will get it to trigger
again.

So by late-ACK-ing the PMI we can miss PMIs that happen between enabling
the PMU and ACKing the PMI.

We should either re-check the overflow mask after the ACK or do the ACK
while the PMU is disabled.


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