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

Jan Kiszka
2007-10-23T16:56:16Z

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?

>
> 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.

>
>
> (once Linux starts executing, it takes a lot of pagefault exits for the
> mmu, and then a lot of hlt exit once it idles).
>
>

Jan

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