Re: [PATCH v5] KVM: halt-polling: poll for the upcoming fire timers

From: Wanpeng Li
Date: Thu May 26 2016 - 07:23:25 EST

2016-05-26 18:30 GMT+08:00 Paolo Bonzini <pbonzini@xxxxxxxxxx>:
> On 26/05/2016 12:26, Paolo Bonzini wrote:
>> As discussed on IRC, I would like to understand why the adaptive
>> adjustment of halt_poll_ns is failing. It seems like you have so few
>> halts that you don't get halt_poll_ns>0. Yet, when the VM halts, it's
>> very close to the timer tick---often enough for this patch to have an
>> effect.
>> Please send a trace of halt_poll_ns_grow and halt_poll_ns_shrink
>> tracepoints, so that we can find out more about this.
> And 30 seconds after I wrote this email, you told me on IRC that the
> guest had HZ=1000 and the module parameter was set to 1 ms in order to
> _really_ benefit from the patch. So basically you could obtain the same
> effect with idle=poll in the guest.
> This explains why your reported results were not so great (as David noted).

Yeah, I will drop the patch.

Wanpeng Li