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Message-ID: <alpine.DEB.2.10.1407221034260.20847@nanos> Date: Tue, 22 Jul 2014 10:39:17 +0200 (CEST) From: Thomas Gleixner <tglx@...utronix.de> To: Peter Zijlstra <peterz@...radead.org> cc: Steven Rostedt <rostedt@...dmis.org>, Darren Hart <dvhart@...ux.intel.com>, Andy Lutomirski <luto@...capital.net>, Andi Kleen <andi@...stfloor.org>, Waiman Long <Waiman.Long@...com>, Ingo Molnar <mingo@...nel.org>, Davidlohr Bueso <davidlohr@...com>, Heiko Carstens <heiko.carstens@...ibm.com>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, Linux API <linux-api@...r.kernel.org>, "linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>, Jason Low <jason.low2@...com>, Scott J Norton <scott.norton@...com>, Robert Haas <robertmhaas@...il.com> Subject: Re: [RFC PATCH 0/5] futex: introduce an optimistic spinning futex 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@...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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