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

Avi Kivity
2007-10-23T16:14:05Z

Jan Kiszka wrote:
>
>> Exiting on a pending interrupt is controlled by the vmcs word
>> PIN_BASED_EXEC_CONTROL, bit PIN_BASED_EXT_INTR_MASK. Can you check (via
>> vmcs_read32()) that the bit is indeed set?
>>
>> [if not, a guest can just enter a busy loop and kill a processor]
>>
>>
>
> I traced it right before and after the asm block, and in all cases
> (including those with low latency exits) it's just 0x1f, which should be
> fine.
>
>

Yes.

> Earlier, I also checked GUEST_INTERRUPTIBILITY_INFO and
> GUEST_ACTIVITY_STATE, but found neither some suspicious state nor a
> difference compared to fast exits.
>

GUEST_* things are unrelated; these talk about whether the guest is
ready to receive an interrupt, but we don't really care, do we?

I don't have any idea why this is happening. This is completely
unrelated to -rt issues -- this is between kvm and the hardware.

Is this on a uniprocessor system? If not, can you try nosmp?

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