linux-kernel - Re: [PATCH v2] KVM: halt-polling: poll if emulated lapic timer will fire soon

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Date:	Thu, 19 May 2016 17:03:37 +0200
From:	Christian Borntraeger <borntraeger@...ibm.com>
To:	Paolo Bonzini <pbonzini@...hat.com>,
	Wanpeng Li <kernellwp@...il.com>, linux-kernel@...r.kernel.org,
	kvm@...r.kernel.org
Cc:	Wanpeng Li <wanpeng.li@...mail.com>,
	Radim Krčmář <rkrcmar@...hat.com>,
	David Matlack <dmatlack@...gle.com>
Subject: Re: [PATCH v2] KVM: halt-polling: poll if emulated lapic timer will
 fire soon

On 05/19/2016 04:56 PM, Paolo Bonzini wrote:
> 
> 
> On 19/05/2016 16:52, Christian Borntraeger wrote:
>>>> Would this work too and be simpler?
>> Hmm, your patch does only fiddle with the grow/shrink logic (which might
>> be a good idea independently of this change), but the original patch 
>> actually takes into account that we have a guaranteed maximum time by a 
>> wakeup timer - IOW we know exactly what the maximum poll time is.
>>
> 
> Yes, it's different.  The question is whether a 10us poll (40,000 clock
> cycles) has an impact even if it's sometimes wrong.

Valid question. As I said, this change might be something good independent from
the original patch. (it might make it unnecessary, though) On the other hand
I can handle ~30 guest entry/exit cycles of a simple exit like diag9c.
Needs measurement.