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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 8C4B7C43334 for ; Mon, 25 Jul 2022 12:51:43 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235265AbiGYMvm (ORCPT ); Mon, 25 Jul 2022 08:51:42 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:55048 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234269AbiGYMvj (ORCPT ); Mon, 25 Jul 2022 08:51:39 -0400 Received: from galois.linutronix.de (Galois.linutronix.de [IPv6:2a0a:51c0:0:12e:550::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id DA6EB65B9 for ; Mon, 25 Jul 2022 05:51:38 -0700 (PDT) From: John Ogness DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1658753497; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=+DLSbK+uqqfR9tgBy7PVplOD816TsUxhQgdpTNoL8a4=; b=SHP1mc3QcooOL8oEqqaq7tVM2b2zDSro9NXni6e0b0/z8oR33P7bymSraNtTllU4PtJwFh gR1/1rimJtiQyaNiHTAe9ssU5Hb3GrMDwcyBxE3oRAsXSYcydAhlbAvH1dxht9I4iYV7fa 47LkzGYbtPpaMJNHnf9LU7mPeOiIUSY+N9uUzrdAVjeCL6Si5QuUlDxn1Fn1kiyF1fx87h erepK/AyjPUNfHztmZYEFDeRTvxA/VtnRY2Ue9b+74T/N4yn7FC+QuKza4+liQIsqekPug 5Bloe2qSEAJ9ZqEuTDR22Z/rzrqVxsUfR5vpIsI+k1iF7KC0ZNjpsT7hoCj3ig== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1658753497; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=+DLSbK+uqqfR9tgBy7PVplOD816TsUxhQgdpTNoL8a4=; b=m8e/Nt2TA/yLOa6we65bLhaa41UXA9Z18cYiXyazITlq4etMLAf4XZ/07dJxsJMh39Dm1M ZxZV2D5IgcNLVJAA== To: Petr Mladek , Sebastian Andrzej Siewior Cc: linux-kernel@vger.kernel.org, Sergey Senozhatsky , Steven Rostedt , Thomas Gleixner Subject: Re: [PATCH v2] printk: Skip console drivers on PREEMPT_RT. In-Reply-To: References: <87y1wn3g3g.fsf@jogness.linutronix.de> <87ilnrn06u.fsf@jogness.linutronix.de> Date: Mon, 25 Jul 2022 14:57:36 +0206 Message-ID: <87zggxgxt3.fsf@jogness.linutronix.de> MIME-Version: 1.0 Content-Type: text/plain Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Petr, On 2022-07-25, Petr Mladek wrote: > From my point, this patch does not make much sense. IMHO, it will > not make mainline usable with PREEMPT_RT. Any serious RT user will > need to revert it and apply a better printk solution from > the out-of-tree RT patchset. The problem is that direct console printing cannot work with PREEMPT_RT, even in a panic situation. And it never will (using "normal" console drivers). PREEMPT_RT is basically mainline now except for the kthread printers and atomic consoles. But these features will not be available in mainline so soon. (Atomic consoles have not gone through the LKML review process at all yet.) We see value in allowing PREEMPT_RT to be available now, even if it means no console printing. You claim "any serious RT user" needs console printing, but for production RT systems, the console is probably disabled anyway. We could solve this with kconfig tricks, making console kconfig options depend on !PREEMPT_RT. But that would cause the console config of users to be disabled, making it more inconvenient for them to turn it back on once these features are available. A software switch (as implemented by Sebastian's patch) may provide the simplest transition. A 5.20 PREEMPT_RT would not have console printing, but a later version (using the same config) would. John