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=-0.6 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS 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 380DDC54FCB for ; Wed, 22 Apr 2020 13:25:38 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 0AC512077D for ; Wed, 22 Apr 2020 13:25:37 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="J2hzEvkM" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726477AbgDVNZh (ORCPT ); Wed, 22 Apr 2020 09:25:37 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:35734 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726046AbgDVNZg (ORCPT ); Wed, 22 Apr 2020 09:25:36 -0400 Received: from merlin.infradead.org (unknown [IPv6:2001:8b0:10b:1231::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 3DDD2C03C1A9 for ; Wed, 22 Apr 2020 06:25:36 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=merlin.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=CckiFsLIOz39/Q99CdZ55wqBbVLH1g4nRz8wpxPrbkI=; b=J2hzEvkMPGlG48+wNy9fP+CcWl YcTklKWQQHlOy8F5/Ptj9q0lsaxA/FIRMuARdiPIg7PgjERwrfOsNnzcxqBN0lMWd6YksC+fmNyT+ U5PnXkc1ltHDU7cqoG3qU0bb7TbuMjaeTQ2uMHjrKOE8DkbjllsGH8iO+BlmcaXH/N52jNQN5kROm y6h+yppf59dwYajiKl96h8gniYbNoIYzgIzgE2FpgXoxXgAor7nqGLec2wDfor+KBJZRmBdSvLdzs zUeRA1TniVcLfiNGOf5Hw1b4OvG64g7S/731L29ZooCzu+RG5kZfCLQhqb2R8NApQgF6/hNJZ/8NV oCP53Ttg==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=noisy.programming.kicks-ass.net) by merlin.infradead.org with esmtpsa (Exim 4.92.3 #3 (Red Hat Linux)) id 1jRFMx-0000wz-IY; Wed, 22 Apr 2020 13:24:51 +0000 Received: from hirez.programming.kicks-ass.net (hirez.programming.kicks-ass.net [192.168.1.225]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client did not present a certificate) by noisy.programming.kicks-ass.net (Postfix) with ESMTPS id BB677300739; Wed, 22 Apr 2020 15:24:48 +0200 (CEST) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id 9FABB25E17E39; Wed, 22 Apr 2020 15:24:48 +0200 (CEST) Date: Wed, 22 Apr 2020 15:24:48 +0200 From: Peter Zijlstra To: Steven Rostedt Cc: mingo@kernel.org, linux-kernel@vger.kernel.org, tglx@linutronix.de, qais.yousef@arm.com, juri.lelli@redhat.com, vincent.guittot@linaro.org, dietmar.eggemann@arm.com, bsegall@google.com, mgorman@suse.de, wim@linux-watchdog.org, Christophe Leroy Subject: Re: [PATCH 16/23] sched,watchdog: Convert to sched_set_fifo() Message-ID: <20200422132448.GH20730@hirez.programming.kicks-ass.net> References: <20200422112719.826676174@infradead.org> <20200422112832.165197058@infradead.org> <20200422085155.7549ca94@gandalf.local.home> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200422085155.7549ca94@gandalf.local.home> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Apr 22, 2020 at 08:51:55AM -0400, Steven Rostedt wrote: > On Wed, 22 Apr 2020 13:27:35 +0200 > Peter Zijlstra wrote: > > > Because SCHED_FIFO is a broken scheduler model (see previous patches) > > take away the priority field, the kernel can't possibly make an > > informed decision. > > > > Effectively changes prio from 99 to 50. > > Hmm, this being a watchdog, and looking at commit 38a1222ae4f364d > ("watchdog: core: make sure the watchdog worker always works") > > I wonder if we should add a sched_set_high(), or have some other kind of > watchdog handler that is guaranteed to trigger. It's FIFO, it'll never win from either a deadline or a stop-task. After that it doesn't matter. fifo_high() is most definitely a bad idea, because then we're back into the whole 'fifo priority' has meaning -- it does not. At least, it doesn't until you've got system design information. Maybe we should rename fifo_low to get away from that. I just drew a blank on a better name there.