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=-2.0 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,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 60739CA9EAE for ; Tue, 29 Oct 2019 13:02:44 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 3375720874 for ; Tue, 29 Oct 2019 13:02:44 +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="xgSb9VSY" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2388223AbfJ2NCn (ORCPT ); Tue, 29 Oct 2019 09:02:43 -0400 Received: from merlin.infradead.org ([205.233.59.134]:40124 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2387901AbfJ2NCm (ORCPT ); Tue, 29 Oct 2019 09:02:42 -0400 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=TXp6GtZA1fnB+a0OnStAdqw3GTFynTzXAdUuYTPfr54=; b=xgSb9VSYh5Q85Nh4M/recBLR7 4U/fKWmRlBQOG6yrhqwqxQPlG12WuXdub/XrZZvPjEuwh0gWIA6HWGWv/oDftAWPl98mRNYRxJESM zQd5XSGZIrLC7DvrFzTGHfo3xMqaoqJai6oOHLbWKqzkDfJ+OIfHC6tkCaYeLXUre1ziCukLiEHcB KBB8o91Cf6iReoBUYGYVLe3yuNNFMu+INako3SUceAZw2Qrp+fu8wCmPw4vMCcDmNB1caurduO/Mg NXTocc55dVJjeyX3hYd11gCjmnH2hXs0xzTzCx+rFo3+qFl4h2nTElRRPskKmOlyHxvulzBxHdf0v 6zB5OA0dw==; 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 1iPR8g-00008h-HL; Tue, 29 Oct 2019 13:02:22 +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 960DE30025A; Tue, 29 Oct 2019 14:01:18 +0100 (CET) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id 345C920D7FEFA; Tue, 29 Oct 2019 14:02:19 +0100 (CET) Date: Tue, 29 Oct 2019 14:02:19 +0100 From: Peter Zijlstra To: Vincent Guittot Cc: Qais Yousef , Ingo Molnar , Steven Rostedt , Juri Lelli , Dietmar Eggemann , Ben Segall , Mel Gorman , linux-kernel Subject: Re: [PATCH v2] sched: rt: Make RT capacity aware Message-ID: <20191029130219.GN4114@hirez.programming.kicks-ass.net> References: <20191009104611.15363-1-qais.yousef@arm.com> <20191029110224.awoi37pdquachqtd@e107158-lin.cambridge.arm.com> <20191029114824.2kb4fygxxx72r3in@e107158-lin.cambridge.arm.com> <20191029124630.ivfbpenue3fw33qt@e107158-lin.cambridge.arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: 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 Tue, Oct 29, 2019 at 01:54:24PM +0100, Vincent Guittot wrote: > On Tue, 29 Oct 2019 at 13:46, Qais Yousef wrote: > > > > On 10/29/19 13:20, Vincent Guittot wrote: > > > > > Making big cores the default CPUs for all RT tasks is not a minor > > > > > change and IMO locality should stay the default behavior when there is > > > > > no uclamp constraint > > > > > > > > How this is affecting locality? The task will always go to the big core, so it > > > > should be local. > > > > > > local with the waker > > > You will force rt task to run on big cluster although waker, data and > > > interrupts can be on little one. > > > So making big core as default is far from always being the best choice > > > > This is loaded with assumptions IMO. AFAICT we don't know what's the best > > choice. > > > > First, the value of uclamp.min is outside of the scope of this patch. Unless > > what you're saying is that when uclamp.min is 1024 then we should NOT choose a > > big cpu then there's no disagreement about what this patch do. If that's what > > you're objecting to please be more specific about how do you see this working > > instead. > > My point is that this patch makes the big cores the default CPUs for > RT tasks which is far from being a minor change and far from being an > obvious default good choice FIFO/RR tasks don't have a bandwidth specification (barring uclamp), therefore we must assume the worst. This is the same principle that has them select max_freq all the time. I think it is a very natural extention of that very principle to place (otherwise unconstrained RT tasks) on big cores.