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

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Message-ID: <m2ua36005b51004060747y1abf15edj28227274844db2e7@mail.gmail.com>
Date:	Tue, 6 Apr 2010 07:47:41 -0700
From:	Ulrich Drepper <drepper@...il.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Avi Kivity <avi@...hat.com>, 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, Apr 6, 2010 at 01:48, Peter Zijlstra <peterz@...radead.org> wrote:
>  try
>  spin
>  try
>  syscall

This is available for a long time in the mutex implementation
(PTHREAD_MUTEX_ADAPTIVE_NP mutex type).  It hasn't show much
improvement if any.  There were some people demanding this support for
as far as I know they are not using it now.  This is adaptive
spinning, learning from previous calls how long to wait.  But it's
still unguided.  There is no way to get information like "the owner
has been descheduled".
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