From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-5.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,MENTIONS_GIT_HOSTING,SPF_HELO_NONE,SPF_PASS autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id B5698C7618F for ; Mon, 15 Jul 2019 16:12:01 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 93DFA2080A for ; Mon, 15 Jul 2019 16:12:01 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730316AbfGOQMA (ORCPT ); Mon, 15 Jul 2019 12:12:00 -0400 Received: from Galois.linutronix.de ([193.142.43.55]:48273 "EHLO Galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729533AbfGOQMA (ORCPT ); Mon, 15 Jul 2019 12:12:00 -0400 Received: from localhost ([127.0.0.1] helo=nanos.tec.linutronix.de) by Galois.linutronix.de with esmtp (Exim 4.80) (envelope-from ) id 1hn3Zw-0000Hc-8z; Mon, 15 Jul 2019 18:11:52 +0200 Message-Id: <20190715150402.798499167@linutronix.de> User-Agent: quilt/0.65 Date: Mon, 15 Jul 2019 17:04:02 +0200 From: Thomas Gleixner To: Linus Torvalds Cc: LKML , Andrew Morton , Greg Kroah-Hartman , Ingo Molnar , Peter Zijlstra , Steven Rostedt , Sebastian Siewior , Paul McKenney , Christoph Hellwig , Tejun Heo , Lukas Bulwahn , Daniel Wagner , Tom Zanussi , Daniel Bristot de Oliveira , Clark Williams , Julia Cartwright , Marc Zyngier , Frederic Weisbecker Subject: [patch 0/1] Kconfig: Introduce CONFIG_PREEMPT_RT Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Linus, please consider to apply the following patch, which introduces the Kconfig symbol CONFIG_PREEMPT_RT. Rationale: The real-time preemption patch set exists for almost 15 years now and while the vast majority of infrastructure and enhancements have found their way into the mainline kernel, the final integration of RT is still missing. Over the course of the last few years, we have worked on reducing the intrusivenness of the RT patches by refactoring kernel infrastructure to be more real-time friendly. Almost all of these changes were benefitial to the mainline kernel on their own, so there was no objection to integrate them. Though except for the still ongoing printk refactoring, the remaining changes which are required to make RT a first class mainline citizen are not longer arguable as immediately beneficial for the mainline kernel. Most of them are either reordering code flows or adding RT specific functionality. But this now has hit a wall and turned into a classic hen and egg problem: Maintainers are rightfully wary vs. these changes as they make only sense if the final integration of RT into the mainline kernel takes place. Adding CONFIG_PREEMPT_RT aims to solve this as a clear sign that RT will be fully integrated into the mainline kernel. The final integration of the missing bits and pieces will be of course done with the same careful approach as we have used in the past. While I'm aware that you are not entirely enthusiastic about that, I think that RT should receive the same treatment as any other widely used out of tree functionality, which we have accepted into mainline over the years. RT has become the de-facto standard real-time enhancement and is shipped by enterprise, embedded and community distros. It's in use throughout a wide range of industries: telecommunications, industrial automation, professional audio, medical devices, data acquisition, automotive - just to name a few major use cases. RT development is backed by a Linuxfoundation project which is supported by major stakeholders of this technology. The funding will continue over the actual inclusion into mainline to make sure that the functionality is neither introducing regressions, regressing itself, nor becomes subject to bitrot. There is also a lifely user community around RT as well, so contrary to the grim situation 5 years ago, it's a healthy project. As RT is still a good vehicle to exercise rarely used code paths and to detect hard to trigger issues, you could at least view it as a QA tool if nothing else. The current state of the RT patches against 5.2 is: 365 files changed, 9396 insertions(+), 3209 deletions(-) When the already queued changes, agreed on changes and the ongoing printk work is taken out then the diffstat is reduced to: 311 files changed, 6567 insertions(+), 1352 deletions(-) Out of the 6567 insertions about 4000 lines are the self contained RT infrastructure (lock substitutions, scheduler addons, etc.). The remaining bits and pieces are smallish changes to places which need to be slightly modified to cope with the RT semantics. The current full RT set can be found here: git://git.kernel.org/pub/scm/linux/kernel/git/rt/linux-rt-devel.git linux-5.2.y-rt Note that aside of the printk changes (which are under flux due to the ongoing review/design discussions) also a large part of the rest is not the final state as these changes still need to be discussed with the relevant maintainers and we are still working hard on refinining them and reducing the impact. So while the big picture is probably good reflected, please take the details with a grain of salt. Thanks, Thomas