Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753612AbaGVIkF (ORCPT ); Tue, 22 Jul 2014 04:40:05 -0400 Received: from www.linutronix.de ([62.245.132.108]:36325 "EHLO Galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751861AbaGVIj7 (ORCPT ); Tue, 22 Jul 2014 04:39:59 -0400 Date: Tue, 22 Jul 2014 10:39:17 +0200 (CEST) From: Thomas Gleixner To: Peter Zijlstra cc: Steven Rostedt , Darren Hart , Andy Lutomirski , Andi Kleen , Waiman Long , Ingo Molnar , Davidlohr Bueso , Heiko Carstens , "linux-kernel@vger.kernel.org" , Linux API , "linux-doc@vger.kernel.org" , Jason Low , Scott J Norton , Robert Haas Subject: Re: [RFC PATCH 0/5] futex: introduce an optimistic spinning futex In-Reply-To: <20140722074719.GV3935@laptop> Message-ID: References: <871tte3bjw.fsf@tassilo.jf.intel.com> <20140721212740.GS3935@laptop> <20140721213457.46623e2f@gandalf.local.home> <20140722074719.GV3935@laptop> User-Agent: Alpine 2.10 (DEB 1266 2009-07-14) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII X-Linutronix-Spam-Score: -1.0 X-Linutronix-Spam-Level: - X-Linutronix-Spam-Status: No , -1.0 points, 5.0 required, ALL_TRUSTED=-1,SHORTCIRCUIT=-0.0001 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 22 Jul 2014, Peter Zijlstra wrote: > Anyway, there is one big fail in the entire futex stack that we 'need' > to sort some day and that is NUMA. Some people (again database people) > explicitly do not use futexes and instead use sysvsem because of this. > > The problem with numa futexes is that because they're vaddr based there > is no (persistent) node information. You always end up having to fall > back to looking in all nodes before you can guarantee there is no > matching futex. > > One way to achieve it is by extending the futex value to include a node > number, but that's obviously a complete ABI break. Then again, it should > be pretty straight fwd, since the node number doesn't need to be part of > the actual atomic update part, just part of the userspace storage. So you want per node hash buckets, right? Fair enough, but how do you make sure, that no thread/process on a different node is fiddling with that "node bound" futex as well? Thanks, tglx -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/