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=-5.5 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 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 7AF4AC433E1 for ; Thu, 13 Aug 2020 07:32:02 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 4D44520771 for ; Thu, 13 Aug 2020 07:32:02 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726526AbgHMHcB (ORCPT ); Thu, 13 Aug 2020 03:32:01 -0400 Received: from mx2.suse.de ([195.135.220.15]:55544 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726072AbgHMHcA (ORCPT ); Thu, 13 Aug 2020 03:32:00 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id 3F77DB1ED; Thu, 13 Aug 2020 07:32:21 +0000 (UTC) Date: Thu, 13 Aug 2020 09:31:58 +0200 From: Petr Mladek To: John Ogness Cc: Linus Torvalds , Sergey Senozhatsky , Sergey Senozhatsky , Steven Rostedt , Greg Kroah-Hartman , Peter Zijlstra , Thomas Gleixner , kexec@lists.infradead.org, Linux Kernel Mailing List Subject: Re: POC: Alternative solution: Re: [PATCH 0/4] printk: reimplement LOG_CONT handling Message-ID: <20200813073158.GI12903@alley> References: <20200717234818.8622-1-john.ogness@linutronix.de> <87blkcanps.fsf@jogness.linutronix.de> <20200811160551.GC12903@alley> <20200812163908.GH12903@alley> <87v9hn2y1p.fsf@jogness.linutronix.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <87v9hn2y1p.fsf@jogness.linutronix.de> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu 2020-08-13 02:30:02, John Ogness wrote: > On 2020-08-12, Petr Mladek wrote: > > So, I have one crazy idea to add one more state bit so that we > > could have: > > > > + committed: set when the data are written into the data ring. > > + final: set when the data block could not longer get reopened > > + reuse: set when the desctiptor/data block could get reused > > > > "final" bit will define when the descriptor could not longer > > get reopened (cleared committed bit) and the data block could > > not get extended. > > I implemented this solution for myself and am currently running more > tests. Some things that I changed from your suggestion: > > 1. I created a separate prb_reserve_cont() function. The reason for this > is because the caller needs to understand what is happening. The caller > is getting an existing record with existing data and must append new > data. The @text_len field of the info reports how long the existing data > is. I see. > So the LOG_CONT handling code in printk.c looks something like this: Yeah, it makes sense. > 2. I haven't yet figured out how to preserve calling context when a > newline appears. For example: > > pr_info("text"); > pr_cont(" 1"); > pr_cont(" 2\n"); > pr_cont("3"); > pr_cont(" 4\n"); > > For "3" the calling context (info, timestamp) is lost because with "2" > the record is finalized. Perhaps the above is invalid usage of LOG_CONT? I am going to answer Sergey's reply. > 3. There are some memory barriers introduced, but it looks like it > shouldn't add too much complexity. Uff. I have hooped for this. > I will continue to refine my working version and post a patch so that we > have something to work with. This looks to be the most promising way > forward. Thanks. Uff, I am happy that it seems working. Several other approaches looked much more complicated or they caused regressions. Best Regards, Petr