linux-kernel - Re: [PATCH RFC 1/2] kvm: Handle undercommitted guest case in PLE handler

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Message-ID: <50644148.5090201@redhat.com>
Date:	Thu, 27 Sep 2012 14:06:32 +0200
From:	Avi Kivity <avi@...hat.com>
To:	Raghavendra K T <raghavendra.kt@...ux.vnet.ibm.com>
CC:	Jiannan Ouyang <ouyang@...pitt.edu>,
	Peter Zijlstra <peterz@...radead.org>,
	Rik van Riel <riel@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...hat.com>,
	Marcelo Tosatti <mtosatti@...hat.com>,
	Srikar <srikar@...ux.vnet.ibm.com>,
	"Nikunj A. Dadhania" <nikunj@...ux.vnet.ibm.com>,
	KVM <kvm@...r.kernel.org>, chegu vinod <chegu_vinod@...com>,
	"Andrew M. Theurer" <habanero@...ux.vnet.ibm.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Srivatsa Vaddagiri <srivatsa.vaddagiri@...il.com>,
	Gleb Natapov <gleb@...hat.com>
Subject: Re: [PATCH RFC 1/2] kvm: Handle undercommitted guest case in PLE
 handler

On 09/27/2012 01:26 PM, Raghavendra K T wrote:
> On 09/27/2012 02:20 PM, Avi Kivity wrote:
>> On 09/25/2012 04:43 PM, Jiannan Ouyang wrote:
>>> I've actually implemented this preempted_bitmap idea.
>>
>> Interesting, please share the code if you can.
>>
>>> However, I'm doing this to expose this information to the guest, so the
>>> guest is able to know if the lock holder is preempted or not before
>>> spining. Right now, I'm doing experiment to show that this idea works.
>>>
>>> I'm wondering what do you guys think of the relationship between the
>>> pv_ticketlock approach and PLE handler approach. Are we going to adopt
>>> PLE instead of the pv ticketlock, and why?
>>
>> Right now we're searching for the best solution.  The tradeoffs are more
>> or less:
>>
>> PLE:
>> - works for unmodified / non-Linux guests
>> - works for all types of spins (e.g. smp_call_function*())
>> - utilizes an existing hardware interface (PAUSE instruction) so likely
>> more robust compared to a software interface
>>
>> PV:
>> - has more information, so it can perform better
> 
> Should we also consider that we always have an edge here for non-PLE
> machine?

True.  The deployment share for these is decreasing rapidly though.  I
hate optimizing for obsolete hardware.


-- 
error compiling committee.c: too many arguments to function
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