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=-2.4 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_PASS,USER_AGENT_MUTT 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 49EBDC43381 for ; Mon, 4 Mar 2019 05:23:43 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 0E4552082F for ; Mon, 4 Mar 2019 05:23:43 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="To6dHLSm" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726035AbfCDFXl (ORCPT ); Mon, 4 Mar 2019 00:23:41 -0500 Received: from mail-pf1-f194.google.com ([209.85.210.194]:44819 "EHLO mail-pf1-f194.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725781AbfCDFXk (ORCPT ); Mon, 4 Mar 2019 00:23:40 -0500 Received: by mail-pf1-f194.google.com with SMTP id a3so2119922pff.11; Sun, 03 Mar 2019 21:23:39 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to:user-agent; bh=OkuYknFFpL7AivetNE74ZYxUSsGQqIr+KvlrxvIEYA8=; b=To6dHLSmguVJcQ7IsXObQSRRFzwddSNq/YFhB6emj4W1bPOcuEpuqmGucj3Mdl1/R7 mH5Gl5fUW4A3v0C+Ov37k/6CuGYA4+9ByvjrNF2o3044WxP0aKuYCqMbprvRhLUr6aHs 9CvkVfuHWODgtP1vXMunysAWjLhzhJ6X0ls56e15XMQWfllv+S6SsKEMTn4i8yw4OHHd ZmoaVmwXiGsncvRKO4da8D0KUNphMrYlAFgcNy9RmSn0hSypnCEjFvyxFGcA9U7Tqslv wzG1TWvHrEsuKQN79enZnV/B4FEb7anUWuB6MNRw9EFiCsS32IUL2ESSZ6Cd0H1hhGND fxMg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to:user-agent; bh=OkuYknFFpL7AivetNE74ZYxUSsGQqIr+KvlrxvIEYA8=; b=ExEKYJiIp9rzCAWqgVNTkThfOPkVhUsD2Y6YcIPEVJKr+WVFE0UnRmFaAXPtN/Nnrb PLKyx1J/4tGTEAJpEVzJGJHH7V7ybqg7LzcPrXra0tSOaHzf6898JLpRO6m0U+/eizod P6sdWW/nKK5JPA5iKI1gF2sCZQYjJiwz04RbZg1tJEeEwXpxs32x5V/YPJAY+0U2bTtC XDUTwng51qzMwDTku34wgB1znCBbEL/yEFImDiMwfUwjHmeABmfcgrLWXGDHqbqLj/CQ n639USSiFqUwmrNvwLJlufAN3yV/J2TKzZ0SoKQGEBjPJVISj5RBIYnoabw9PwZ73Voz Ylgw== X-Gm-Message-State: APjAAAWf+SKDmSm8q/qwNILqkhLLZgNtBNE2CJplEWQm9nCTpJ9Wr3gz /7hmF+kRvyVMDB4vt4u/L/su3WCX X-Google-Smtp-Source: APXvYqxsee3m4H4yWkTIl37aOYTYGLEfztr3R1ZBuolHsVD5ah/D9FsgcmmIqah257xqDp0anipcbQ== X-Received: by 2002:a63:5a5e:: with SMTP id k30mr16926317pgm.345.1551677019633; Sun, 03 Mar 2019 21:23:39 -0800 (PST) Received: from localhost ([175.223.38.45]) by smtp.gmail.com with ESMTPSA id o76sm8731578pfa.156.2019.03.03.21.23.37 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Sun, 03 Mar 2019 21:23:38 -0800 (PST) Date: Mon, 4 Mar 2019 14:23:35 +0900 From: Sergey Senozhatsky To: John Ogness Cc: Sergey Senozhatsky , linux-kernel@vger.kernel.org, Peter Zijlstra , Petr Mladek , Steven Rostedt , Daniel Wang , Andrew Morton , Linus Torvalds , Greg Kroah-Hartman , Alan Cox , Jiri Slaby , Peter Feiner , linux-serial@vger.kernel.org, Sergey Senozhatsky Subject: Re: [RFC PATCH v1 00/25] printk: new implementation Message-ID: <20190304052335.GA6648@jagdpanzerIV> References: <20190212143003.48446-1-john.ogness@linutronix.de> <20190213025520.GA5803@jagdpanzerIV> <874l9721hf.fsf@linutronix.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <874l9721hf.fsf@linutronix.de> User-Agent: Mutt/1.11.3 (2019-02-01) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On (02/13/19 15:43), John Ogness wrote: > On 2019-02-13, Sergey Senozhatsky wrote: > >> - A dedicated kernel thread is created for printing to all consoles in > >> a fully preemptible context. > > > > How do you handle sysrq- printouts on systems which can't > > schedule printk-kthread? > > If those sysrq printouts are at the emergency loglevel (which most are), > then they are printed immediately to the emergency consoles. This has > already proved useful for our own kernel debugging work. For example, > currently sysrq-z for very large traces result in messages being dropped > because of printk buffer overflows. But with the emergency console we > always see the full trace buffer. Are we sure that all systems will always have ->atomic console(-s) enabled? Is it possible to convert all console drivers to ->atomic? fbcon, for instance (with scrolling and font scaling, etc)? If there are setups which can be fully !atomic (in terms of console output) then we, essentially, have a fully preemptible kthread printk implementation. > Because you have already done so much work and experimentation with > printk-kthreads, I feel like many of your comments are related to your > kthread work in this area. Really the big design change I make with my > printk-kthread is that it is only for non-critical messages. For > anything critical, users should rely on an emergency console. Fair point. Well maybe my printk-kthread comments are not utterly unreasonable, but who knows :) -ss