Re: High vm-exit latencies during kvm boot-up/shutdown

Jan Kiszka
2007-10-24T08:37:56Z

Avi Kivity wrote:
> Jan Kiszka wrote:
>> Avi Kivity wrote:
>>
>>> Jan Kiszka wrote:
>>>
>>>> It's both: -rt tests were performed with nosmp (-rt locks up under SMP
>>>> here), and the Xenomai tests, including the last instrumentation, ran in
>>>> SMP mode. So I tend to exclude SMP effects.
>>>>
>>>> Do you have some suggestion how to analyse what the guest is executing
>>>> while those IRQs are delayed? As I said, I suspect some interaction of
>>>> the Bochs BIOS is triggering the effect, because it only shows up (with
>>>> a Linux guest) before the BIOS prints the first messages.
>>>>
>>>>
>>> The guest is probably spinning. Can you try modifying
>>> user/test/bootstrap.S, around the start label, to look like
>>>
>>> start: jmp start
>>>
>>> ? This can then be executed with
>>>
>>> user/kvmctl user/test/bootstrap user/test/access.flat
>>>
>> Access flat is not being built here (kvm-48), or I'm pressing the wrong
>> button. Forcing it with "make test/access.flat" gives build errors.
>> What's the trick?
>>
>>
>
> Sorry, it's x86_64 specific. Just pick any other small file, since it
> won't be executed anyway, and there are no format requirements.
>
>>> This will give us something consistent to test. The output of kvm_stat
>>> should also be interesting (should show exits and irq_exits advancing at
>>> 10K/sec).
>>>
>> You probably mean with the artificial test, not with qemu/kvm.
>>
>>
>
> Yes.
>

I ran

user/kvmctl user/test/bootstrap user/test/smp.flat

with the busy loop hacked into bootstrap, but I got no latency spots
this time. And what should I look for in the output of kvm_stat?

Jan

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