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=-2.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,USER_AGENT_NEOMUTT 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 91E9DC4321E for ; Fri, 7 Sep 2018 08:24:35 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 49BB32075B for ; Fri, 7 Sep 2018 08:24:35 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 49BB32075B Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=arm.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727721AbeIGNEW (ORCPT ); Fri, 7 Sep 2018 09:04:22 -0400 Received: from usa-sjc-mx-foss1.foss.arm.com ([217.140.101.70]:56572 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727579AbeIGNEW (ORCPT ); Fri, 7 Sep 2018 09:04:22 -0400 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.72.51.249]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 2EC567A9; Fri, 7 Sep 2018 01:24:32 -0700 (PDT) Received: from queper01-lin (queper01-lin.Emea.Arm.com [10.4.13.27]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 30DBF3F557; Fri, 7 Sep 2018 01:24:28 -0700 (PDT) Date: Fri, 7 Sep 2018 09:24:23 +0100 From: Quentin Perret To: Dietmar Eggemann Cc: peterz@infradead.org, rjw@rjwysocki.net, linux-kernel@vger.kernel.org, linux-pm@vger.kernel.org, gregkh@linuxfoundation.org, mingo@redhat.com, morten.rasmussen@arm.com, chris.redpath@arm.com, patrick.bellasi@arm.com, valentin.schneider@arm.com, vincent.guittot@linaro.org, thara.gopinath@linaro.org, viresh.kumar@linaro.org, tkjos@google.com, joel@joelfernandes.org, smuckle@google.com, adharmap@codeaurora.org, skannan@codeaurora.org, pkondeti@codeaurora.org, juri.lelli@redhat.com, edubezval@gmail.com, srinivas.pandruvada@linux.intel.com, currojerez@riseup.net, javi.merino@kernel.org Subject: Re: [PATCH v6 07/14] sched/topology: Introduce sched_energy_present static key Message-ID: <20180907082139.ogsdxambyryhgsu4@queper01-lin> References: <20180820094420.26590-1-quentin.perret@arm.com> <20180820094420.26590-8-quentin.perret@arm.com> <20180906092955.tq27mhzfkovo2ehn@queper01-lin> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: NeoMutt/20171215 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thursday 06 Sep 2018 at 16:49:47 (-0700), Dietmar Eggemann wrote: > I would prefer a sched_feature. I guess it has to be disabled by default so > that other systems don't have to check rcu_dereference(rd->pd) in the wakeup > path. Right, this is what I had in mind too. I guess downstream kernels can always carry a patch that changes the default if they want it enabled without messing around in userspace. > But since at the beginning EAS will be the only user of the EM there is no > need to change the static key sched_energy_present right now. Indeed, I could add a patch introducing this sched_feat in the series that migrates IPA to using the EM framework (to be posted later). It is just not required until we have a new user. However that IPA-related patchset would then change the default behaviour for users who used to get EAS enabled automatically, but wouldn't after updating their kernel (meaning they'd now have to flip switches by hand whereas it used to "just work"). Not sure if that qualifies as "breaking users" (cf. Linus' rule #1 of kernel development) ... Thanks, Quentin