linux-kernel - Re: [PATCH RFC 0/2] kvm: Improving undercommit,overcommit scenarios in PLE handler

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Date:	Fri, 28 Sep 2012 16:13:05 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	habanero@...ux.vnet.ibm.com
Cc:	Raghavendra K T <raghavendra.kt@...ux.vnet.ibm.com>,
	Avi Kivity <avi@...hat.com>, "H. Peter Anvin" <hpa@...or.com>,
	Marcelo Tosatti <mtosatti@...hat.com>,
	Ingo Molnar <mingo@...hat.com>, Rik van Riel <riel@...hat.com>,
	Srikar <srikar@...ux.vnet.ibm.com>,
	"Nikunj A. Dadhania" <nikunj@...ux.vnet.ibm.com>,
	KVM <kvm@...r.kernel.org>, Jiannan Ouyang <ouyang@...pitt.edu>,
	chegu vinod <chegu_vinod@...com>,
	LKML <linux-kernel@...r.kernel.org>,
	Srivatsa Vaddagiri <srivatsa.vaddagiri@...il.com>,
	Gleb Natapov <gleb@...hat.com>,
	Andrew Jones <drjones@...hat.com>
Subject: Re: [PATCH RFC 0/2] kvm: Improving undercommit,overcommit scenarios
 in PLE handler

On Fri, 2012-09-28 at 06:40 -0500, Andrew Theurer wrote:
> It will be interesting to see how this behaves with a very high lock
> activity in a guest.  Once the scheduler defers preemption, is it for
> a
> fixed amount of time, or does it know to cut the deferral short as
> soon
> as the lock depth is reduced [by x]? 

Since the locks live in a guest/userspace, we don't even know they're
held at all, let alone when state changes.

Also, afaik PLE simply exits the guest whenever you do a busy-wait,
there's no guarantee its due to a lock at all, we could be waiting for a
'virtual' hardware resource or whatnot.


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