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Date: Wed, 07 Apr 2010 20:41:22 -0700 From: Darren Hart <dvhltc@...ibm.com> To: drepper@...il.com CC: Thomas Gleixner <tglx@...utronix.de>, Alan Cox <alan@...rguk.ukuu.org.uk>, Peter Zijlstra <peterz@...radead.org>, Avi Kivity <avi@...hat.com>, 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 drepper@...il.com wrote: > On Tue, Apr 6, 2010 at 16:16, Thomas Gleixner <tglx@...utronix.de> wrote: >> I know that you can do any weird stuff with the futex value, but I >> don't see the "dramatic" limitation. Care to elaborate ? > > If we have to fill in the PID we can represent only three states in a > futex: 0, PID, -PID. Today we can represent 2^32 states. Quite a > difference. For general futexes sure, but not for robust or PI mutexes. Having adaptive futexes be based on the TID|WAITERS_FLAG policy certainly isn't breaking new ground, and is consistent with the other kernel-side futex locking implementations. However, I agree that a FUTEX_SET_WAIT_ADAPTIVE sort of call might be very powerful. However, that might be just academic until I can show an improvement with adaptive futexes. >> The per thread pinned page would be unconditional, right ? > > Only if the process would be using these adaptive mutexes. It could be > conditional. What about the concern of this TLS approach only working for process private locks? I would very much like to make this work for both shared and private locks. Thanks, -- Darren Hart IBM Linux Technology Center Real-Time Linux Team -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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