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=-2.1 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 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 7DABDC33CB1 for ; Wed, 15 Jan 2020 14:57:17 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 51E282465A for ; Wed, 15 Jan 2020 14:57:17 +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="hxhlUpBM" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729125AbgAOO5Q (ORCPT ); Wed, 15 Jan 2020 09:57:16 -0500 Received: from merlin.infradead.org ([205.233.59.134]:53340 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726248AbgAOO5P (ORCPT ); Wed, 15 Jan 2020 09:57:15 -0500 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:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Id: List-Help:List-Unsubscribe:List-Subscribe:List-Post:List-Owner:List-Archive; bh=zYvfHEkAzcG6x0JYAatDwISXBtxZj7+56kXRS6nreOY=; b=hxhlUpBMsRkFVGusknWLZvV2P fmooJozPgiNWV0gIxROWkfciN+O9o2snxCNwrPmc57F1o6SKlNQGDYeY1/HR+l69yEbBYSoHxw12C hGzrvvL7cUfpAebtT0xv8fyGyNggD6Cj4FnDs2EPZMy0/56iDrxIVlGE+JWtBoZzPdnUsDRaUc0Y8 fbahBgG4MMb2jvAoJzcmPAij46QLbY0/lOS7f2gcD8S/RYeTTjE2IOkojWYxyJlrmLZphontdzyQZ PxGZHunLCFhQxpvl65UZt3w2nbABTj8P88XzsKj3tlZI5wp5v/zsALxXtTqVlRcxA5a/TT7rdpXf+ b6q46yVBQ==; 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 1irk6C-00073U-S9; Wed, 15 Jan 2020 14:56:49 +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 CFA9E30257C; Wed, 15 Jan 2020 15:55:08 +0100 (CET) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id 361DD2B6C6D7F; Wed, 15 Jan 2020 15:56:45 +0100 (CET) Date: Wed, 15 Jan 2020 15:56:45 +0100 From: Peter Zijlstra To: David Laight Cc: 'Steven Rostedt' , 'Vincent Guittot' , Viresh Kumar , Ingo Molnar , Juri Lelli , Dietmar Eggemann , Ben Segall , Mel Gorman , linux-kernel Subject: Re: sched/fair: scheduler not running high priority process on idle cpu Message-ID: <20200115145645.GM2827@hirez.programming.kicks-ass.net> References: <212fabd759b0486aa8df588477acf6d0@AcuMS.aculab.com> <20200114115906.22f952ff@gandalf.local.home> <5ba2ae2d426c4058b314c20c25a9b1d0@AcuMS.aculab.com> <20200114124812.4d5355ae@gandalf.local.home> <878a35a6642d482aa0770a055506bd5e@AcuMS.aculab.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <878a35a6642d482aa0770a055506bd5e@AcuMS.aculab.com> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Jan 15, 2020 at 12:44:19PM +0000, David Laight wrote: > Code that runs with a spin-lock held (or otherwise disables preemption) > for significant periods probably ought to be detected and warned. > I'm not sure of a suitable limit, 100us is probably excessive on x86. Problem is, without CONFIG_PREEMPT_COUNT (basically only PREEMPT/PREEMPT_RT) we can't even tell. And I think we tried adding warnings to things like softirq, but then we get into arguments with the pure performance people on how allowing it longer will make their benchmarks go faster. There really is no silver bullet here :/