From mboxrd@z Thu Jan 1 00:00:00 1970 Return-path: Received: from mx2.suse.de ([195.135.220.15]) by merlin.infradead.org with esmtps (Exim 4.92.3 #3 (Red Hat Linux)) id 1jtBrk-0004YQ-UF for kexec@lists.infradead.org; Wed, 08 Jul 2020 15:20:10 +0000 Date: Wed, 8 Jul 2020 17:20:05 +0200 From: Petr Mladek Subject: Re: [PATCH v4 0/4] printk: replace ringbuffer Message-ID: <20200708152005.GF4751@alley> References: <20200707145932.8752-1-john.ogness@linutronix.de> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20200707145932.8752-1-john.ogness@linutronix.de> List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "kexec" Errors-To: kexec-bounces+dwmw2=infradead.org@lists.infradead.org To: John Ogness Cc: Andrea Parri , Sergey Senozhatsky , Paul McKenney , Peter Zijlstra , Greg Kroah-Hartman , kexec@lists.infradead.org, linux-kernel@vger.kernel.org, Steven Rostedt , Sergey Senozhatsky , Thomas Gleixner , Linus Torvalds On Tue 2020-07-07 17:05:28, John Ogness wrote: > Hello, > > Here is a v4 for the first series to rework the printk > subsystem. The v3 is here [0]. This first series > only replaces the existing ringbuffer implementation. No locking > is removed. The semantics/behavior of printk are kept the same > except for a minor optimization that is reverted (patch 3). > > Despite minor changes to the ringbuffer code since v3 (comments, > function names, very minor refactoring), the ringbuffer logic > itself has not changed. And, in particular, the memory barriers > have been exactly preserved from v3. For this reason I deem it > appropriate to keep Paul's reviewed by tag (patch 2). > > RFC patches for various userspace tools to dump the kernel log > are available: crash [1], makedumpfile [2], kexec-tools [3]. > > Finally, I would like to thank some people/organizations that > helped with performing ringbuffer stress tests on big or rare > hardware that I do not have access to: > > - Prarit Bhargava of Red Hat (x86_64, ppc64le power8) > - Michael Cree of Debian (alpha) > - Jeff Scheel of OSU Open Source Lab (ppc64le power8 kvm) OK, I think that we are ready to try this in linux-next. I am going to push it there via printk/linux.git. I have a good feeling about the patchset. The great thing is that the access is still synchronized using logbuf_lock so that we do not have to deal with races for the moment. Of course, there are still many potential problems. The following comes to my mind: + Bugs in the algorithm logic or implementation might prevent showing any messages on consoles or via syslog or /dev/kmsg. We did our best to avoid it. + Debugging tools accessing the buffer directly would need to understand the new structure. Fortunately John provided patches for the most prominent ones. + Small devices might complain about less effective use of memory. Part of descriptors and dictionaries ring buffers might stay unused. But it hopefully could get tuned. This is basically just a start of the journey. I hope that it will be a good one. Best Regards, Petr _______________________________________________ kexec mailing list kexec@lists.infradead.org http://lists.infradead.org/mailman/listinfo/kexec