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From: Paolo Bonzini <pbonzini@redhat.com>
To: Wanpeng Li <kernellwp@gmail.com>,
	linux-kernel@vger.kernel.org, kvm@vger.kernel.org
Cc: "Wanpeng Li" <wanpeng.li@hotmail.com>,
	"Radim Krčmář" <rkrcmar@redhat.com>,
	"David Matlack" <dmatlack@google.com>,
	"Christian Borntraeger" <borntraeger@de.ibm.com>,
	"Yang Zhang" <yang.zhang.wz@gmail.com>
Subject: Re: [PATCH v5] KVM: halt-polling: poll for the upcoming fire timers
Date: Thu, 26 May 2016 12:30:20 +0200	[thread overview]
Message-ID: <7cac7435-1f65-6a60-e2f5-ed5c285ea0ae@redhat.com> (raw)
In-Reply-To: <c66b94e0-45db-b8bd-1d63-c3d781afd5ce@redhat.com>



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

  reply	other threads:[~2016-05-26 10:30 UTC|newest]

Thread overview: 7+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-05-25  2:47 Wanpeng Li
2016-05-26 10:26 ` Paolo Bonzini
2016-05-26 10:30   ` Paolo Bonzini [this message]
2016-05-26 11:23     ` Wanpeng Li
2016-05-26 20:33   ` yunhong jiang
2016-05-27  9:49     ` Paolo Bonzini
2016-05-28  0:14       ` yunhong jiang

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