linux-kernel - Re: [PATCH V2 0/6][RFC] futex: FUTEX_LOCK with optional adaptive spinning

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Message-ID: <1270562948.1595.442.camel@laptop>
Date:	Tue, 06 Apr 2010 16:09:08 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Avi Kivity <avi@...hat.com>
Cc:	Darren Hart <dvhltc@...ibm.com>, linux-kernel@...r.kernel.org,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...e.hu>,
	Eric Dumazet <eric.dumazet@...il.com>,
	"Peter W. Morreale" <pmorreale@...ell.com>,
	Rik van Riel <riel@...hat.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Gregory Haskins <ghaskins@...ell.com>,
	Sven-Thorsten Dietrich <sdietrich@...ell.com>,
	Chris Mason <chris.mason@...cle.com>,
	John Cooper <john.cooper@...rd-harmonic.com>,
	Chris Wright <chrisw@...s-sol.org>
Subject: Re: [PATCH V2 0/6][RFC] futex: FUTEX_LOCK with optional adaptive
 spinning

On Tue, 2010-04-06 at 16:41 +0300, Avi Kivity wrote:
> On 04/06/2010 04:35 PM, Peter Zijlstra wrote:
> > On Tue, 2010-04-06 at 16:28 +0300, Avi Kivity wrote:
> >    
> >> Yes, but that's the best case for spinning.  You could simply use a
> >> userspace spinlock in this case.
> >>      
> > Userspace spinlocks are evil.. they should _never_ be used.
> >    
> 
> But in this case they're fastest.  If we don't provide a non-evil 
> alternative, people will use them.
> 

That's what FUTEX_LOCK is about.

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