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SubjectRe: [PATCH] KVM: add halt_attempted_poll to VCPU stats
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On 16/09/2015 12:12, Christian Borntraeger wrote:
> I am looking into a case right now, where auto polling goes
> completely nuts on my system:
>
> guest1: 8vcpus guest2: 1 vcpu
> iperf with 25 process (-P25) from guest1 to guest2.
>
> I/O interrupts on s390 are floating (pending on all CPUs) so on
> ALL VCPUs that go to sleep, polling will consider any pending
> network interrupt as successful poll. So with auto polling the
> guest consumes up to 5 host CPUs without auto polling only 1.
> Reducing halt_poll_ns to 100000 seems to work (goes back to
> 1 cpu).
>
> The proper way might be to feedback the result of the
> interrupt dequeue into the heuristics. Don't know yet how
> to handle that properly.

I think it's simplest to disable halt_poll_ns by default on s390. On
x86, for example, you can mark interrupts so that they _can_ be
delivered to all CPUs but only one will get it.

You can add a Kconfig symbol for that to other architectures, and not s390.

Paolo


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