Date: Tue, 6 Apr 2010 17:53:11 +0100
From: Alan Cox <alan@lxorguk.ukuu.org.uk>
To: Avi Kivity <avi@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>, Darren Hart <dvhltc@us.ibm.com>,
       linux-kernel@vger.kernel.org, Thomas Gleixner <tglx@linutronix.de>,
       Ingo Molnar <mingo@elte.hu>, Eric Dumazet <eric.dumazet@gmail.com>,
       "Peter W. Morreale" <pmorreale@novell.com>,
       Rik van Riel <riel@redhat.com>, Steven Rostedt <rostedt@goodmis.org>,
       Gregory Haskins <ghaskins@novell.com>,
       Sven-Thorsten Dietrich <sdietrich@novell.com>,
       Chris Mason <chris.mason@oracle.com>,
       John Cooper <john.cooper@third-harmonic.com>,
       Chris Wright <chrisw@sous-sol.org>
Subject: Re: [PATCH V2 0/6][RFC] futex: FUTEX_LOCK with optional adaptive
 spinning
Message-ID: <20100406175311.11e5d3a8@lxorguk.ukuu.org.uk>
In-Reply-To: <4BBB5CEF.6060803@redhat.com>
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	<4BBB36FA.4020008@redhat.com>
	<1270560931.1595.342.camel@laptop>
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	<4BBB5CEF.6060803@redhat.com>
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> That works for the uncontended case.  For the contended case, the waiter 
> and the owner have to go into the kernel and back out to transfer 
> ownership.

If you insist on doing it that way yes, but knowing the lock owner is
likely to be away for a while also lets you do things like punt work
either by picking another work package in the meantime, or by queueing
the work you can't do on a list the pre-empted lock owner will review
before dropping the lock.

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