linux-kernel - Re: Preemptable Ticket Spinlock

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Message-ID: <5175A277.5080208@redhat.com>
Date:	Mon, 22 Apr 2013 16:49:59 -0400
From:	Rik van Riel <riel@...hat.com>
To:	Jiannan Ouyang <ouyang@...pitt.edu>
CC:	Peter Zijlstra <peterz@...radead.org>,
	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 04/22/2013 04:46 PM, Jiannan Ouyang wrote:

> It would still be very interesting to conduct more experiments to
> compare these two, to see if the fairness enforced by pv_lock is
> mandatory, and if preemptable-lock outperforms pv_lock in most cases,
> and how do they work with PLE.

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.

The fairness is only compromised in a limited way and in certain
circumstances, so I am not too worried about that.

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