linux-kernel - Re: Preemptable Ticket Spinlock

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Date:	Tue, 23 Apr 2013 10:33:00 +0530
From:	Raghavendra K T <raghavendra.kt@...ux.vnet.ibm.com>
To:	Peter Zijlstra <peterz@...radead.org>
CC:	Rik van Riel <riel@...hat.com>,
	Jiannan Ouyang <ouyang@...pitt.edu>,
	LKML <linux-kernel@...r.kernel.org>,
	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 04/23/2013 02:31 AM, Peter Zijlstra wrote:
> On Mon, 2013-04-22 at 16:49 -0400, Rik van Riel wrote:
>> Given the fairly high cost of rescheduling a VCPU (which is likely
>> to include an IPI), versus the short hold time of most spinlocks,
>> I have the strong suspicion that your approach would win.
>
>    https://lkml.org/lkml/2012/5/2/101
>
> If you schedule too often your SPIN_THRESHOLD is far too low.
>
> Anyway.. performance can't be that bad, otherwise Jeremey would have
> spend as much time on it as he did.

When I experimented last time ideal SPIN_THRESHOLD for PLE machine,
was around 4k, 8k. Jeremy's experiment was on a non-PLE machine AFAIK,
which complemented PLE feature in a nice way with 2k threshold.

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