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

From	Paolo Bonzini <pbonzini@redhat.com>
Newsgroups	linux.kernel
Subject	Re: [PATCH v5] KVM: halt-polling: poll for the upcoming fire timers
Date	2016-05-26 12:40 +0200
Message-ID	<rD0RP-5hu-9@gated-at.bofh.it> (permalink)
References	<rCx3s-3y6-3@gated-at.bofh.it> <rD0Ia-5eg-25@gated-at.bofh.it>
Organization	linux.* mail to news gateway

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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).

Thanks,

Paolo

Thread

[PATCH v5] KVM: halt-polling: poll for the upcoming fire timers Wanpeng Li <kernellwp@gmail.com> - 2016-05-25 04:50 +0200
  Re: [PATCH v5] KVM: halt-polling: poll for the upcoming fire timers Paolo Bonzini <pbonzini@redhat.com> - 2016-05-26 12:30 +0200
    Re: [PATCH v5] KVM: halt-polling: poll for the upcoming fire timers Paolo Bonzini <pbonzini@redhat.com> - 2016-05-26 12:40 +0200
      Re: [PATCH v5] KVM: halt-polling: poll for the upcoming fire timers Wanpeng Li <kernellwp@gmail.com> - 2016-05-26 13:30 +0200
    Re: [PATCH v5] KVM: halt-polling: poll for the upcoming fire timers yunhong jiang <yunhong.jiang@linux.intel.com> - 2016-05-26 22:50 +0200
      Re: [PATCH v5] KVM: halt-polling: poll for the upcoming fire timers Paolo Bonzini <pbonzini@redhat.com> - 2016-05-27 11:50 +0200
        Re: [PATCH v5] KVM: halt-polling: poll for the upcoming fire timers yunhong jiang <yunhong.jiang@linux.intel.com> - 2016-05-28 02:30 +0200

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