linux-kernel - Re: Preemptable Ticket Spinlock

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Message-ID: <5175A38D.4070002@hp.com>
Date:	Mon, 22 Apr 2013 13:54:37 -0700
From:	Chegu Vinod <chegu_vinod@...com>
To:	Jiannan Ouyang <ouyang@...pitt.edu>
CC:	Peter Zijlstra <peterz@...radead.org>,
	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>,
	"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 4/22/2013 1:50 PM, Jiannan Ouyang wrote:
> 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.
> .
>
Thanks for sharing your patch. 'am waiting for your v2 patch(es) and 
then let you any review feedback. Hoping to verify your changes on a 
large box (PLE enabled) and get back to you with some data...

Thanks
Vinod
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