From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S934643AbdDHB13 (ORCPT ); Fri, 7 Apr 2017 21:27:29 -0400 Received: from bombadil.infradead.org ([65.50.211.133]:60202 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933506AbdDHB1P (ORCPT ); Fri, 7 Apr 2017 21:27:15 -0400 Date: Fri, 7 Apr 2017 18:27:07 -0700 From: Darren Hart To: Peter Zijlstra Cc: tglx@linutronix.de, mingo@kernel.org, juri.lelli@arm.com, rostedt@goodmis.org, xlpang@redhat.com, bigeasy@linutronix.de, linux-kernel@vger.kernel.org, mathieu.desnoyers@efficios.com, jdesfossez@efficios.com, bristot@redhat.com Subject: Re: [PATCH -v6 12/13] futex: futex_unlock_pi() determinism Message-ID: <20170408012707.GB16143@fury> References: <20170322103547.756091212@infradead.org> <20170322104152.112378812@infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170322104152.112378812@infradead.org> User-Agent: Mutt/1.7.1 (2016-10-04) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Mar 22, 2017 at 11:35:59AM +0100, Peter Zijlstra wrote: > The problem with returning -EAGAIN when the waiter state mismatches is > that it becomes very hard to proof a bounded execution time on the prove > operation. And seeing that this is a RT operation, this is somewhat an RT > important. > > While in practise; given the previous patch; it will be very unlikely Heh, that's not what semicolons are for ;-) Commas here, or a parenthetical. > to ever really take more than one or two rounds, proving so becomes > rather hard. > > However, now that modifying wait_list is done while holding both > hb->lock and wait_lock, we can avoid the scenario entirely if we > acquire wait_lock while still holding hb-lock. Doing a hand-over, > without leaving a hole. Nice :) -- Darren Hart VMware Open Source Technology Center