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 85DF3410 for ; Thu, 15 Oct 2015 02:20:05 +0000 (UTC) Received: from cdptpa-oedge-vip.email.rr.com (cdptpa-outbound-snat.email.rr.com [107.14.166.228]) by smtp1.linuxfoundation.org (Postfix) with ESMTP id E390490 for ; Thu, 15 Oct 2015 02:20:04 +0000 (UTC) Date: Wed, 14 Oct 2015 22:20:02 -0400 From: Steven Rostedt To: Tim Bird Message-ID: <20151014222002.3f345ac3@grimm.local.home> In-Reply-To: <561EAD4D.6080901@sonymobile.com> References: <20151013124230.1a082d28@gandalf.local.home> <20151014092041.282117ac@gandalf.local.home> <20151014112225.26771952@gandalf.local.home> <20151014143244.19c2512a@gandalf.local.home> <561EAD4D.6080901@sonymobile.com> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit 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 Wed, 14 Oct 2015 12:30:21 -0700 Tim Bird wrote: REPLY ALL Tim! I didn't notice this email till I saw it as QotW on LWN. > Check out Xenomai. (xenomai.org) I think that's what many embedded folk use > if they find that RT-PREEMPT does not meet their needs. Xenomai 3.0 > allows you to use their system either on top of RT-PREEMPT or > on top of their Cobalt kernel sitting next to (or in front of, > depending on your perspective) the Linux kernel. > > Sony used RT-PREEMPT in some products, and a dual-kernel in others, > and isolated CPUs running something else (usually uItron) in yet others. > > Personally, I'd be happy to see RT-PREEMPT go in - there are certain use BTW, it's PREEMPT_RT not RT-PREEMPT. > cases for it. I'd also like to see the NOHZ stuff go in as well. It should > solve a set of problems for isolating RT tasks without sacrificing > performance on the non-RT CPUs. And finally, I wouldn't mind putting > a non-Linux RT kernel like Cobalt (oh the horrors) into mainline as well. > Each of these approaches has their strengths and weaknesses. Linux is, > after all, whatever we say it is - and it could easily have a small RT > micro-kernel as part of the source base as well. > > AFAIK the patent issues that plagued the dual-kernel approach are now > behind us, so this might be a good area of investigation. > > I've long felt that RT-PREEMPT was sucking the oxygen out of getting other, > technically valid, approaches to RT with Linux into mainline. I'm perfectly fine with working together with Xenomai. When you need a few microsecond latencies, that may be the best tool. I don't think they are mutually exclusive, but actually complement each other quite nicely. -- Steve