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=-0.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=no 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 26817C4CEC9 for ; Wed, 18 Sep 2019 09:05:40 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 03E9120640 for ; Wed, 18 Sep 2019 09:05:40 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728079AbfIRJFj (ORCPT ); Wed, 18 Sep 2019 05:05:39 -0400 Received: from Galois.linutronix.de ([193.142.43.55]:45369 "EHLO Galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725909AbfIRJFi (ORCPT ); Wed, 18 Sep 2019 05:05:38 -0400 Received: from localhost ([127.0.0.1] helo=vostro.local) by Galois.linutronix.de with esmtp (Exim 4.80) (envelope-from ) id 1iAVty-0002uu-W5; Wed, 18 Sep 2019 11:05:31 +0200 From: John Ogness To: Sergey Senozhatsky Cc: Steven Rostedt , Linus Torvalds , Thomas Gleixner , Peter Zijlstra , Petr Mladek , Andrea Parri , Sergey Senozhatsky , Brendan Higgins , Greg Kroah-Hartman , LKML , Theodore Ts'o , Paul Turner , Daniel Vetter , Prarit Bhargava Subject: Re: printk meeting at LPC References: <20190905143118.GP2349@hirez.programming.kicks-ass.net> <20190905121101.60c78422@oasis.local.home> <87k1acz5rx.fsf@linutronix.de> <20190918012546.GA12090@jagdpanzerIV> <20190917220849.17a1226a@oasis.local.home> <20190918023654.GB15380@jagdpanzerIV> <20190918051933.GA220683@jagdpanzerIV> <87h85anj85.fsf@linutronix.de> <20190918081012.GB37041@jagdpanzerIV> Date: Wed, 18 Sep 2019 11:05:28 +0200 In-Reply-To: <20190918081012.GB37041@jagdpanzerIV> (Sergey Senozhatsky's message of "Wed, 18 Sep 2019 17:10:12 +0900") Message-ID: <877e66nfdz.fsf@linutronix.de> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/23.4 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2019-09-18, Sergey Senozhatsky wrote: >> Each console has its own iterator. This iterators will need to >> advance, regardless if the message was printed via write() or >> write_atomic(). > > Great. > > ->atomic_write() path will make sure that kthread is parked or will > those compete for uart port? A cpu-lock (probably per-console) will be used to synchronize the two. Unlike my RFCv1, we want to keep the cpu-lock out of the console drivers and we want it to be less aggressive (using trylock's instead of spinning). This should make the cpu-lock less "dangerous". I talked with PeterZ, Thomas, and PetrM about how this can be implemented, but there may still be some corner cases. I would like to put everything together now so that we can run and test if the decisions made in that meeting hold up for all the cases. I think it will be easier to identify/add the missing pieces, once we have it coded. John Ogness