Re: Host latency peaks due to kvm-intel

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

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Jan Kiszka wrote:
> Gregory Haskins wrote:
>   
>> 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.
>>     
>
> I did, see above.
>   

Ah, sorry.  It wasn't clear what "instrumenation" was or if you felt it
was definitively pinpointed.  :P

Regards,
-Greg



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