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a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=g8y3Kv95ejyL7msYqyPIoRMuCM9aKky/CsOCvaHvzKM=; b=qhQatlpTZ7W6ynYcamhkQ9zPU7HC9YopKVOoYLVUBOPcfMNXqT2mUibZZ1oSqdO103 /rWXQ/tSa2YVG8x597yBEKdrL0PTEsTHSunE+Z8HKQaaeEBDl4pjneJD6nZpcZ2/T/7b bGhb3kR2bzRLFI23vNK+kQyHMl4rkEvGnt4kIRC2ZMyFI9PgeZxFEIy2OCycDUFzbfUR YytsFVDLEFbx2wGekyShy+P93sQ3CP7fQCAkF8w3c0mOcN8R9CEJR3PTCnOHyzAqSzeu tCAAwBfVaae1pDQxm9yLWiK7ARisbs2SVM3CUQCC9z3PSnHpTHsmwyBMJ9AWZ6D6fWIM a33w== X-Gm-Message-State: APjAAAWgdbqzVhkHufjFCq6AiyUcRZTErTgz/7Y8d5rwQO3OAgBGc+/T JlobwWefEIDaMbU+Dl6hRWE2OP/qPGQpmD/n8GL9iA== X-Google-Smtp-Source: APXvYqzHzf9qj/gQvrMhsVZj/mUBqCeBT0v/95hThrViwKN4rfJkI0AUVqq0YGCyoYWqoiClXSsdpDtSyx/K8KYU40o= X-Received: by 2002:a19:ab11:: with SMTP id u17mr7519021lfe.78.1573230521103; Fri, 08 Nov 2019 08:28:41 -0800 (PST) MIME-Version: 1.0 References: <20191106030542.868541-1-dima@arista.com> <20191106092039.GT4131@hirez.programming.kicks-ass.net> <10db6fa1-5b17-ebe6-09e0-6335e09e4db8@arista.com> <20191106203440.GH3079@worktop.programming.kicks-ass.net> In-Reply-To: <20191106203440.GH3079@worktop.programming.kicks-ass.net> From: Dmitry Safonov Date: Fri, 8 Nov 2019 16:28:30 +0000 Message-ID: Subject: Re: [PATCH 00/50] Add log level to show_stack() To: Peter Zijlstra X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20191108_082847_334865_F0BE37C4 X-CRM114-Status: GOOD ( 20.30 ) X-BeenThere: linux-riscv@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Juri Lelli , linux-sh@vger.kernel.org, Catalin Marinas , Ben Segall , Guo Ren , Pavel Machek , Vincent Guittot , Paul Burton , Michael Ellerman , Geert Uytterhoeven , Mel Gorman , Jiri Slaby , Matt Turner , uclinux-h8-devel@lists.sourceforge.jp, Len Brown , linux-pm@vger.kernel.org, Heiko Carstens , linux-um@lists.infradead.org, Thomas Gleixner , Dietmar Eggemann , Richard Henderson , Greg Kroah-Hartman , "Rafael J. Wysocki" , LKML , Ralf Baechle , Paul Mackerras , Andrew Morton , linux-ia64@vger.kernel.org, Tetsuo Handa , James Hogan , "James E.J. Bottomley" , Max Filippov , Vincent Chen , Ingo Molnar , linux-s390@vger.kernel.org, linux-c6x-dev@linux-c6x.org, Yoshinori Sato , linux-hexagon@vger.kernel.org, Helge Deller , "open list:TENSILICA XTENSA PORT \(xtensa\)" , Vasily Gorbik , Aurelien Jacquiot , linux-m68k@lists.linux-m68k.org, Stafford Horne , linux-arm-kernel@lists.infradead.org, Chris Zankel , Tony Luck , Douglas Anderson , Benjamin Herrenschmidt , Dmitry Safonov <0x7f454c46@gmail.com>, Will Deacon , Daniel Thompson , Brian Cain , Christian Borntraeger , kgdb-bugreport@lists.sourceforge.net, linux-snps-arc@lists.infradead.org, Fenghua Yu , Borislav Petkov , Jeff Dike , Steven Rostedt , Ivan Kokshaysky , Greentime Hu , Guan Xuetao , linux-parisc@vger.kernel.org, linux-alpha@vger.kernel.org, Ley Foon Tan , "David S. Miller" , Rich Felker , Petr Mladek , "H. Peter Anvin" , sparclinux@vger.kernel.org, linux-riscv@lists.infradead.org, Anton Ivanov , Jonas Bonn , Richard Weinberger , X86 ML , Russell King , clang-built-linux@googlegroups.com, Ingo Molnar , Mark Salter , Albert Ou , Stefan Kristiansson , openrisc@lists.librecores.org, Paul Walmsley , Michal Simek , Vineet Gupta , linux-mips@vger.kernel.org, Sergey Senozhatsky , Palmer Dabbelt , Jason Wessel , nios2-dev@lists.rocketboards.org, linuxppc-dev@lists.ozlabs.org Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-riscv" Errors-To: linux-riscv-bounces+infradead-linux-riscv=archiver.kernel.org@lists.infradead.org On 11/6/19 8:34 PM, Peter Zijlstra wrote: > On Wed, Nov 06, 2019 at 04:27:33PM +0000, Dmitry Safonov wrote: [..] >> Sorry, I should have tried to describe better. >> >> I'm trying to remove external users of console_loglevel by following >> reasons: > > I suppose since all my machines have 'debug ignore_loglevel > earlyprintk=serial,ttyS0,115200 console=ttyS0,115200' I don't have this > experience. Yeah, I remember you avoid all those functionalities of printk(), fair enough. On the other side, regular users and I'm betting most of the non-tuned distributions use /proc/sys/kernel/printk by default. (Checking on my Arch & Fedora - loglevel 4 from the box) >> - changing console_loglevel on SMP means that unwanted messages from >> other CPUs will appear (that have lower log level) >> - on UMP unwanted messages may appear if the code is preempted while it >> hasn't set the console_loglevel back to old >> - rising console_loglevel to print wanted message(s) may not work at all >> if printk() has being delayed and the console_loglevel is already set >> back to old value > > Sure, frobbing the global console_loglevel is bad. > >> I also have patches in wip those needs to print backtrace with specific >> loglevel (higher when it's critical, lower when it's notice and >> shouldn't go to serial console). > > (everything always should go to serial, serial is awesome :-) Personally I agree. Unfortunately, here @Arista there are switches (I'm speaking about the order of thousands at least) those have baud-rate 9600. It's a bit expensive being elaborate with such setup. >> Besides on local tests I see hits those have headers (messages like >> "Backtrace: ") without an actual backtrace and the reverse - a backtrace >> without a reason for it. It's quite annoying and worth addressing by >> syncing headers log levels to backtraces. > > I suppose I'm surprised there are backtraces that are not important. > Either badness happened and it needs printing, or the user asked for it > and it needs printing. > > Perhaps we should be removing backtraces if they're not important > instead of allowing to print them as lower loglevels? Well, the use-case for lower log-level is that everything goes into logs (/var/log/dmesg or /var/log/messages whatever rsyslog has settting). That has it's value: - after a failure (i.e. panic) messages, those were only signs that something goes wrong can be seen in logs which can give ideas what has happened. - before the failure, those messages go to telemetry and can be auto-magically processed remotely to take a decision (e.g. balance the traffic away). I wish all the information could be gathered in the userspace, but many existing kernel/driver messages are valuable. A more detailed example is hung task detector: we want to have the backtrace for a task that is in uninterruptible state too long, but only in logs as printing on serial console may lead to holding console lock and watchdog. Besides customer notifications and investigations, I see the value of such "bottleneck" warnings during long-running integration tests. Thanks, Dmitry _______________________________________________ linux-riscv mailing list linux-riscv@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-riscv