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=-9.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, USER_AGENT_GIT autolearn=unavailable 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 353DCC54E8D for ; Mon, 11 May 2020 15:41:26 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 201BB206DB for ; Mon, 11 May 2020 15:41:26 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730474AbgEKPlZ (ORCPT ); Mon, 11 May 2020 11:41:25 -0400 Received: from foss.arm.com ([217.140.110.172]:34946 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726934AbgEKPlY (ORCPT ); Mon, 11 May 2020 11:41:24 -0400 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 2B6EB31B; Mon, 11 May 2020 08:41:24 -0700 (PDT) Received: from e107158-lin.cambridge.arm.com (e107158-lin.cambridge.arm.com [10.1.195.21]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id A0D8A3F68F; Mon, 11 May 2020 08:41:21 -0700 (PDT) From: Qais Yousef To: Peter Zijlstra , Ingo Molnar Cc: Randy Dunlap , Qais Yousef , Jonathan Corbet , Juri Lelli , Vincent Guittot , Dietmar Eggemann , Steven Rostedt , Ben Segall , Mel Gorman , Luis Chamberlain , Kees Cook , Iurii Zaikin , Quentin Perret , Valentin Schneider , Patrick Bellasi , Pavan Kondeti , linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org Subject: [PATCH 2/2] Documentation/sysctl: Document uclamp sysctl knobs Date: Mon, 11 May 2020 16:40:53 +0100 Message-Id: <20200511154053.7822-2-qais.yousef@arm.com> X-Mailer: git-send-email 2.17.1 In-Reply-To: <20200511154053.7822-1-qais.yousef@arm.com> References: <20200511154053.7822-1-qais.yousef@arm.com> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Uclamp exposes 3 sysctl knobs: * sched_util_clamp_min * sched_util_clamp_max * sched_util_clamp_min_rt_default Document them in sysctl/kernel.rst. Signed-off-by: Qais Yousef CC: Jonathan Corbet CC: Juri Lelli CC: Vincent Guittot CC: Dietmar Eggemann CC: Steven Rostedt CC: Ben Segall CC: Mel Gorman CC: Luis Chamberlain CC: Kees Cook CC: Iurii Zaikin CC: Quentin Perret CC: Valentin Schneider CC: Patrick Bellasi CC: Pavan Kondeti CC: linux-doc@vger.kernel.org CC: linux-kernel@vger.kernel.org CC: linux-fsdevel@vger.kernel.org --- Changes in v5: * Improve the wording about the lazy update and the relationship to sched_util_clamp_min (Patrick) Documentation/admin-guide/sysctl/kernel.rst | 57 +++++++++++++++++++++ 1 file changed, 57 insertions(+) diff --git a/Documentation/admin-guide/sysctl/kernel.rst b/Documentation/admin-guide/sysctl/kernel.rst index 0d427fd10941..6cd3cb0e22c0 100644 --- a/Documentation/admin-guide/sysctl/kernel.rst +++ b/Documentation/admin-guide/sysctl/kernel.rst @@ -940,6 +940,63 @@ Enables/disables scheduler statistics. Enabling this feature incurs a small amount of overhead in the scheduler but is useful for debugging and performance tuning. +sched_util_clamp_min: +===================== + +Max allowed *minimum* utilization. + +Default value is 1024, which is the maximum possible value. + +It means that any requested uclamp.min value cannot be greater than +sched_util_clamp_min, i.e., it is restricted to the range +[0:sched_util_clamp_min]. + +sched_util_clamp_max: +===================== + +Max allowed *maximum* utilization. + +Default value is 1024, which is the maximum possible value. + +It means that any requested uclamp.max value cannot be greater than +sched_util_clamp_max, i.e., it is restricted to the range +[0:sched_util_clamp_max]. + +sched_util_clamp_min_rt_default: +================================ + +By default Linux is tuned for performance. Which means that RT tasks always run +at the highest frequency and most capable (highest capacity) CPU (in +heterogeneous systems). + +Uclamp achieves this by setting the requested uclamp.min of all RT tasks to +1024 by default, which effectively boosts the tasks to run at the highest +frequency and biases them to run on the biggest CPU. + +This knob allows admins to change the default behavior when uclamp is being +used. In battery powered devices particularly, running at the maximum +capacity and frequency will increase energy consumption and shorten the battery +life. + +This knob is only effective for RT tasks which the user hasn't modified their +requested uclamp.min value via sched_setattr() syscall. + +This knob will not escape the range constraint imposed by sched_util_clamp_min +defined above. + +For example if + + sched_util_clamp_min_rt_default = 800 + sched_util_clamp_min = 600 + +Then the boost will be clamped to 600 because 800 is outside of the permissible +range of [0:600]. This could happen for instance if a powersave mode will +restrict all boosts temporarily by modifying sched_util_clamp_min. As soon as +this restriction is lifted, the requested sched_util_clamp_min_rt_default +will take effect. + +Any modification is applied lazily to tasks and is effective starting from +their next wakeup. seccomp ======= -- 2.17.1