From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from smtp1.linuxfoundation.org (smtp1.linux-foundation.org [172.17.192.35]) by mail.linuxfoundation.org (Postfix) with ESMTPS id 1B295282 for ; Tue, 13 Oct 2015 22:48:40 +0000 (UTC) Received: from mx2.suse.de (mx2.suse.de [195.135.220.15]) by smtp1.linuxfoundation.org (Postfix) with ESMTPS id 75819128 for ; Tue, 13 Oct 2015 22:48:39 +0000 (UTC) Date: Wed, 14 Oct 2015 00:48:37 +0200 From: "Luis R. Rodriguez" To: Steven Rostedt Message-ID: <20151013224837.GG14464@wotan.suse.de> References: <20151013124230.1a082d28@gandalf.local.home> <2823307.1o7LnhjveU@vostro.rjw.lan> <20151013221941.GF14464@wotan.suse.de> <20151013183934.0d1ac4bc@gandalf.local.home> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20151013183934.0d1ac4bc@gandalf.local.home> Cc: ksummit-discuss@lists.linuxfoundation.org Subject: Re: [Ksummit-discuss] [TECH TOPIC] Mainlining PREEMPT_RT List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On Tue, Oct 13, 2015 at 06:39:34PM -0400, Steven Rostedt wrote: > On Wed, 14 Oct 2015 00:19:41 +0200 > "Luis R. Rodriguez" wrote: > > > On Wed, Oct 14, 2015 at 12:40:10AM +0200, Rafael J. Wysocki wrote: > > > On Tuesday, October 13, 2015 12:42:30 PM Steven Rostedt wrote: > > > > > > > > Now that it was announced in Dublin last week that mainlining > > > > PREEMPT_RT has funding, I would like to propose a tech topic to discuss > > > > what is needed to be done in the near future. > > > > > > > > Thomas Gleixner and his minions will be doing the brunt of the work, > > > > but there's issues that need to be addressed with the rest of the > > > > kernel. The various topics would include: > > > > > > > > CPU hotplug > > > > preempt_disable and local_irq_disable annotations > > > > new timer_wheel implementation > > > > simple waitqueues > > > > trylock boosting > > > > > > > > Several of the Real Time developers will be present at kernel summit. I > > > > think this would be a great opportunity to have them be able to sit > > > > down together and discuss the remaining issues. > > > > > > Well, that's not limited to the RT developers even. > > > > > > Good topic. > > > > How much of this is the above topics Vs lack of good semantics in general, or > > code which needs love / good design? I ask as we have a few 'semantic' > > discussions, and I have a feeling there might be overlap. > > Well, CPU hotplug needs a rewrite. Preempt disabling and irq disabling > needs some commentary on what they are actually protecting. The timer > wheel is showing its age. Simple waitqueues can help make the majority > of the cases less complex. But the trylock boosting is -rt only. > > As always, when -rt goes into mainline, we try hard to make sure those > changes improve mainline. Thus, we change designs and clean up code as > -rt goes in. We've been doing that since 2004, and nobody took > notice ;-) That is, people saw improvements and never knew those > improvements were solely to get -rt working better. That's what I was alluding to -- what lessons have been learned here that we have needed over time to make that happen, which to others not in the know, perhaps have been transparent / nothing new other than yet-another-kernel-feature / kernel-bell-whistle. Luis