linux-kernel - Re: Preemptable Ticket Spinlock

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Message-id: <CAJocwcf2=+oWmn3EvNnCA5U81LPA=Ue8=RNYDJb_J6wNYmgNMQ@mail.gmail.com>
Date:	Mon, 22 Apr 2013 16:50:40 -0400
From:	Jiannan Ouyang <ouyang@...pitt.edu>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Rik van Riel <riel@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Raghavendra K T <raghavendra.kt@...ux.vnet.ibm.com>,
	Avi Kivity <avi.kivity@...il.com>,
	Gleb Natapov <gleb@...hat.com>, Ingo Molnar <mingo@...hat.com>,
	Marcelo Tosatti <mtosatti@...hat.com>,
	Srikar <srikar@...ux.vnet.ibm.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	"Nikunj A. Dadhania" <nikunj@...ux.vnet.ibm.com>,
	KVM <kvm@...r.kernel.org>, Thomas Gleixner <tglx@...utronix.de>,
	Chegu Vinod <chegu_vinod@...com>,
	"Andrew M. Theurer" <habanero@...ux.vnet.ibm.com>,
	Srivatsa Vaddagiri <srivatsa.vaddagiri@...il.com>,
	Andrew Jones <drjones@...hat.com>,
	Karen Noel <knoel@...hat.com>
Subject: Re: Preemptable Ticket Spinlock

On Mon, Apr 22, 2013 at 4:44 PM, Peter Zijlstra <peterz@...radead.org> wrote:
> On Mon, 2013-04-22 at 16:32 -0400, Rik van Riel wrote:
>>
>> IIRC one of the reasons was that the performance improvement wasn't
>> as obvious.  Rescheduling VCPUs takes a fair amount of time, quite
>> probably more than the typical hold time of a spinlock.
>
> IIRC it would spin for a while before blocking..
>
> /me goes re-read some of that thread...
>
> Ah, its because PLE is curing most of it.. !PLE it had huge gains but
> apparently nobody cares about !PLE hardware anymore :-)
>

For now, I don't know how good it can work with PLE. But I think it
should save the time of VMEXIT on PLE machine.
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