linux-kernel - Re: Preemptable Ticket Spinlock

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Message-ID: <1366631460.4443.3.camel@laptop>
Date:	Mon, 22 Apr 2013 13:51:00 +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 Sun, 2013-04-21 at 17:12 -0400, Rik van Riel wrote:
> 
> If we always incremented the ticket number by 2 (instead of 1), then
> we could use the lower bit of the ticket number as the spinlock.

ISTR that paravirt ticket locks already do that and use the lsb to
indicate the unlock needs to perform wakeups.

Also, since all of this is virt nonsense, shouldn't it live in the
paravirt ticket lock code and leave the native code as is?

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