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

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Message-Id: <20120925232122.e6fabbc5c472148aeec70234@gmail.com>
Date:	Tue, 25 Sep 2012 23:21:22 +0900
From:	Takuya Yoshikawa <takuya.yoshikawa@...il.com>
To:	Avi Kivity <avi@...hat.com>
Cc:	Raghavendra K T <raghavendra.kt@...ux.vnet.ibm.com>,
	Rik van Riel <riel@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	"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>, Jiannan Ouyang <ouyang@...pitt.edu>,
	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 Tue, 25 Sep 2012 10:12:49 +0200
Avi Kivity <avi@...hat.com> wrote:

> It will.  The tradeoff is between false-positive costs (undercommit) and
> true positive costs (overcommit).  I think undercommit should perform
> well no matter what.
> 
> If we utilize preempt notifiers to track overcommit dynamically, then we
> can vary the spin time dynamically.  Keep it long initially, as we get
> more preempted vcpus make it shorter.

What will happen if we pin each vcpu thread to some core?
I don't want to see so many vcpu threads moving around without
being pinned at all.

In that case, we don't want to make KVM do any work of searching
a vcpu thread to yield to.

Thanks,
	Takuya
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