From patchwork Thu Jul 7 07:15:53 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Lukasz Luba X-Patchwork-Id: 588415 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 48F99CCA479 for ; Thu, 7 Jul 2022 07:16:15 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234533AbiGGHQO (ORCPT ); Thu, 7 Jul 2022 03:16:14 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:38654 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230004AbiGGHQN (ORCPT ); Thu, 7 Jul 2022 03:16:13 -0400 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id 077F02FFCD; Thu, 7 Jul 2022 00:16:13 -0700 (PDT) Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 21360113E; Thu, 7 Jul 2022 00:16:13 -0700 (PDT) Received: from e123648.arm.com (unknown [10.57.11.194]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPA id DFAC73F70D; Thu, 7 Jul 2022 00:16:09 -0700 (PDT) From: Lukasz Luba To: linux-kernel@vger.kernel.org, linux-pm@vger.kernel.org Cc: daniel.lezcano@linaro.org, amitk@kernel.org, rui.zhang@intel.com, lukasz.luba@arm.com, viresh.kumar@linaro.org, rafael@kernel.org, dietmar.eggemann@arm.com, nm@ti.com, sboyd@kernel.org, sudeep.holla@arm.com, cristian.marussi@arm.com, matthias.bgg@gmail.com, linux-mediatek@lists.infradead.org, linux-arm-kernel@lists.infradead.org Subject: [PATCH v2 2/4] Documentation: EM: Switch to micro-Watts scale Date: Thu, 7 Jul 2022 08:15:53 +0100 Message-Id: <20220707071555.10085-3-lukasz.luba@arm.com> X-Mailer: git-send-email 2.17.1 In-Reply-To: <20220707071555.10085-1-lukasz.luba@arm.com> References: <20220707071555.10085-1-lukasz.luba@arm.com> Precedence: bulk List-ID: X-Mailing-List: linux-pm@vger.kernel.org The EM now uses the micro-Watts scale for the power values. Update related documentation to reflect that fact. Fix also a problematic sentence in the doc "to:" which triggers test scripts complaining about wrong email address. Reviewed-by: Daniel Lezcano Signed-off-by: Lukasz Luba --- Documentation/power/energy-model.rst | 14 +++++++------- 1 file changed, 7 insertions(+), 7 deletions(-) diff --git a/Documentation/power/energy-model.rst b/Documentation/power/energy-model.rst index feb257b7f350..ef341be2882b 100644 --- a/Documentation/power/energy-model.rst +++ b/Documentation/power/energy-model.rst @@ -20,20 +20,20 @@ possible source of information on its own, the EM framework intervenes as an abstraction layer which standardizes the format of power cost tables in the kernel, hence enabling to avoid redundant work. -The power values might be expressed in milli-Watts or in an 'abstract scale'. +The power values might be expressed in micro-Watts or in an 'abstract scale'. Multiple subsystems might use the EM and it is up to the system integrator to check that the requirements for the power value scale types are met. An example can be found in the Energy-Aware Scheduler documentation Documentation/scheduler/sched-energy.rst. For some subsystems like thermal or powercap power values expressed in an 'abstract scale' might cause issues. These subsystems are more interested in estimation of power used in the past, -thus the real milli-Watts might be needed. An example of these requirements can +thus the real micro-Watts might be needed. An example of these requirements can be found in the Intelligent Power Allocation in Documentation/driver-api/thermal/power_allocator.rst. Kernel subsystems might implement automatic detection to check whether EM registered devices have inconsistent scale (based on EM internal flag). Important thing to keep in mind is that when the power values are expressed in -an 'abstract scale' deriving real energy in milli-Joules would not be possible. +an 'abstract scale' deriving real energy in micro-Joules would not be possible. The figure below depicts an example of drivers (Arm-specific here, but the approach is applicable to any architecture) providing power costs to the EM @@ -98,7 +98,7 @@ Drivers are expected to register performance domains into the EM framework by calling the following API:: int em_dev_register_perf_domain(struct device *dev, unsigned int nr_states, - struct em_data_callback *cb, cpumask_t *cpus, bool milliwatts); + struct em_data_callback *cb, cpumask_t *cpus, bool microwatts); Drivers must provide a callback function returning tuples for each performance state. The callback function provided by the driver is free @@ -106,10 +106,10 @@ to fetch data from any relevant location (DT, firmware, ...), and by any mean deemed necessary. Only for CPU devices, drivers must specify the CPUs of the performance domains using cpumask. For other devices than CPUs the last argument must be set to NULL. -The last argument 'milliwatts' is important to set with correct value. Kernel +The last argument 'microwatts' is important to set with correct value. Kernel subsystems which use EM might rely on this flag to check if all EM devices use the same scale. If there are different scales, these subsystems might decide -to: return warning/error, stop working or panic. +to return warning/error, stop working or panic. See Section 3. for an example of driver implementing this callback, or Section 2.4 for further documentation on this API @@ -137,7 +137,7 @@ The .get_cost() allows to provide the 'cost' values which reflect the efficiency of the CPUs. This would allow to provide EAS information which has different relation than what would be forced by the EM internal formulas calculating 'cost' values. To register an EM for such platform, the -driver must set the flag 'milliwatts' to 0, provide .get_power() callback +driver must set the flag 'microwatts' to 0, provide .get_power() callback and provide .get_cost() callback. The EM framework would handle such platform properly during registration. A flag EM_PERF_DOMAIN_ARTIFICIAL is set for such platform. Special care should be taken by other frameworks which are using EM