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

Avi Kivity
2007-10-23T17:05:09Z

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.

--
Do not meddle in the internals of kernels, for they are subtle and quick to panic.