linux-kernel - Re: Preemptable Ticket Spinlock

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Message-ID: <1366664518.8337.21.camel@laptop>
Date:	Mon, 22 Apr 2013 23:01:58 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Rik van Riel <riel@...hat.com>
Cc:	Jiannan Ouyang <ouyang@...pitt.edu>,
	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, 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.

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