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

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Message-ID: <1270567769.20295.18.camel@laptop>
Date:	Tue, 06 Apr 2010 17:29:29 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Darren Hart <dvhltc@...ibm.com>
Cc:	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>, Avi Kivity <avi@...hat.com>
Subject: Re: [PATCH V2 0/6][RFC] futex: FUTEX_LOCK with optional adaptive
 spinning

On Mon, 2010-04-05 at 13:23 -0700, Darren Hart wrote:
> Lastly, I should mention that these results all underperform a simple
> pthread_mutex_lock()/pthread_mutex_unlock() pair. I'm looking into why but felt
> I was overdue in sharing what I have to date. A test comparing this to a
> sched_yield() style userspace spinlock would probably be more appropraite.

This really should be able to out-perform a regular pthread_mutex_lock()
we saw a significant performance gain when we added adaptive spins to
the kernel mutex implementation, so I'd expect a gain on the futex one
as well.


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