Re: Host latency peaks due to kvm-intel

[Gregory Haskins <gregory.haskins@gmail.com>]

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Jan Kiszka wrote:
> Hi,
>
> did anyone recently tried current KVM for Intel over some real-time
> Linux? I'm seeing more than 500 us latency peaks on the host,
> specifically during VM startup. This applies to both 2.6.29.6-rt23 and
> Xenomai/I-pipe. For -rt, I both tried the included (patched) KVM modules
> as well as kvm.git head with some additionally required -rt fixes.
> Xenomai ran over a 2.6.30 kernel with my own KVM-enabler patch.
>
> Early instrumentation actually points to the guest exit itself: I added
> markers right before and after the assembly part of vmx_vcpu_run, and
> further instrumentation reports that the next host APIC tick should go
> off right inside guest mode. But KVM leaves the switching part 500 us
> too late in that case - as if guest exit on external IRQs was disabled.
>
> Will debug this further, but I'm also curious to hear other user
> experiences.
>
> Jan
>
>   
Hi Jan,
  Did you try to run with latency-tracer enabled?  If not, this may
pinpoint the source for you.

Regards,
-Greg


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