From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752092AbdI2Ign (ORCPT ); Fri, 29 Sep 2017 04:36:43 -0400 Received: from bombadil.infradead.org ([65.50.211.133]:58354 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750847AbdI2Igl (ORCPT ); Fri, 29 Sep 2017 04:36:41 -0400 Date: Fri, 29 Sep 2017 10:36:35 +0200 From: Peter Zijlstra To: Gerd Gerats Cc: tglx@linutronix.de, mingo@redhat.com, dvhart@infradead.org, LKML Subject: Re: [RFC] futex: hashbucket as list of futex instead of waiters Message-ID: <20170929083635.dgvywknme6lhmjtd@hirez.programming.kicks-ass.net> References: <20170910213324.GA24252@pluto.fritz.box> <20170928105814.cfzsyi42asybctfo@hirez.programming.kicks-ass.net> <20170928223932.GA874@pluto.fritz.box> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170928223932.GA874@pluto.fritz.box> User-Agent: NeoMutt/20170609 (1.8.3) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Sep 29, 2017 at 12:39:32AM +0200, Gerd Gerats wrote: > > > > So I suppose the purpose of that plist in futex is to enable waking up > > the highest prio waiter, but with the advent of SCHED_DEADLINE that no > > longer works. > > I do not understand, plist is the original data structure. I assume, it works > together with SCHED_DEADLINE. plist does not work well with DEADLINE, all deadline tasks will get lumped together at prio -1; prio as a single integer doesn't really work for DEADLINE. We've converted the RT-mutes over to RB-trees a fair while ago; see commit: fb00aca47440 ("rtmutex: Turn the plist into an rb-tree") > Or is there something on the way not pressent in 4.13. Thomas held off on converting futex to rb-trees because, as he said elsewhere in this thread, he's worried about the performance impact on futexes.