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

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Message-ID: <20100406175415.3e4a57df@lxorguk.ukuu.org.uk>
Date:	Tue, 6 Apr 2010 17:54:15 +0100
From:	Alan Cox <alan@...rguk.ukuu.org.uk>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	Avi Kivity <avi@...hat.com>, Darren Hart <dvhltc@...ibm.com>,
	Peter Zijlstra <peterz@...radead.org>,
	linux-kernel@...r.kernel.org, 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

> > IMO the best solution is to spin in userspace while the lock holder is
> > running, fall into the kernel when it is scheduled out.
> 
> That's just not realistic as user space has no idea whether the lock
> holder is running or not and when it's scheduled out without a syscall :)

Which is the real problem that wants addressing and can be addressed very
cheaply. That would bring us up to par with 1970s RTOS environments ;)

Alan
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