linux-kernel - Re: [PATCH RFC 2/2] kvm: Be courteous to other VMs in overcommitted scenario in PLE handler

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Message-ID: <50607F9B.7090701@redhat.com>
Date:	Mon, 24 Sep 2012 17:43:23 +0200
From:	Avi Kivity <avi@...hat.com>
To:	Peter Zijlstra <peterz@...radead.org>
CC:	Raghavendra K T <raghavendra.kt@...ux.vnet.ibm.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>,
	"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 2/2] kvm: Be courteous to other VMs in overcommitted
 scenario in PLE handler

On 09/24/2012 05:34 PM, Peter Zijlstra wrote:
> On Mon, 2012-09-24 at 17:26 +0200, Avi Kivity wrote:
>> I think this is a no-op these (CFS) days.  To get schedule() to do
>> anything, you need to wake up a task, or let time pass, or block.
>> Otherwise it will see that nothing has changed and as far as it's
>> concerned you're still the best task to be running (otherwise it
>> wouldn't have picked you in the first place). 
> 
> Time could have passed enough before calling this that there's now a
> different/more eligible task around to schedule.

Wouldn't this correspond to the scheduler interrupt firing and causing a
reschedule?  I thought the timer was programmed for exactly the point in
time that CFS considers the right time for a switch.  But I'm basing
this on my mental model of CFS, not CFS itself.

> Esp. for a !PREEMPT kernel this is could be significant.


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