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From: Ulrich Drepper <drepper@gmail.com>
Date: Sat, 10 Apr 2010 16:53:33 -0700
Message-ID: <i2ta36005b51004101653ka0411bc6z5841f35cbd1e41d1@mail.gmail.com>
Subject: Re: [PATCH V2 0/6][RFC] futex: FUTEX_LOCK with optional adaptive 
	spinning
To: Alan Cox <alan@lxorguk.ukuu.org.uk>
Cc: Darren Hart <dvhltc@us.ibm.com>, Peter Zijlstra <peterz@infradead.org>,
       Avi Kivity <avi@redhat.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>
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On Sat, Apr 10, 2010 at 16:35, Alan Cox <alan@lxorguk.ukuu.org.uk> wrote:
> You only need one page per 4096 threads

Very expensive.  Each cache line would be fought over by 64 threads.
Constant RFOs make context switches significantly slower.

At most 4096/64 = 64 threads should share one page.  One page would
still cover almost all processes.
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