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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 24EE7C4332F for ; Thu, 6 Jan 2022 11:54:12 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S238656AbiAFLyK (ORCPT ); Thu, 6 Jan 2022 06:54:10 -0500 Received: from foss.arm.com ([217.140.110.172]:52440 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S238456AbiAFLyJ (ORCPT ); Thu, 6 Jan 2022 06:54:09 -0500 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 D17C213A1; Thu, 6 Jan 2022 03:54:08 -0800 (PST) Received: from [10.57.11.40] (unknown [10.57.11.40]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 9A2AB3F774; Thu, 6 Jan 2022 03:54:07 -0800 (PST) Subject: Re: [PATCH v2][RFC 1/2] Implement Ziegler-Nichols Heuristic To: daniel.lezcano@linaro.org Cc: rafael@kernel.org, linux-kernel@vger.kernel.org, amitk@kernel.org, Chetankumar Mistry , rui.zhang@intel.com, linux-pm@vger.kernel.org References: <20211217184907.2103677-1-chetan.mistry@arm.com> From: Lukasz Luba Message-ID: <23c3480a-c46b-f049-5758-d11124367190@arm.com> Date: Thu, 6 Jan 2022 11:54:05 +0000 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.14.0 MIME-Version: 1.0 In-Reply-To: <20211217184907.2103677-1-chetan.mistry@arm.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Daniel, Could you have a look at this, please? On 12/17/21 6:49 PM, Chetankumar Mistry wrote: > Implement the Ziegler-Nichols Heuristic algorithm to better > estimate the PID Coefficients for a running platform. > The values are tuned to minimuse the amount of overshoot in > the temperature of the platform and subsequently minimise > the number of switches for cdev states. > > Signed-off-by: Chetankumar Mistry This is the continuation of the previous idea to have better k_* values. You might remember this conversation [1]. I've spent some time researching papers how and what can be done in this field and if possible to plumb in to the kernel. We had internal discussions (~2017) of one method fuzzy-logic that I found back then, but died at the begging not fitting into this IPA kernel specific environment and user-space. Your suggestion with observing undershooting and overshooting results sparked better idea. I thought it's worth to invest in it but I didn't have time. We are lucky, Chetan was designated to help me and experiment/implement/test these ideas and here is the patch set. He's chosen the Ziegler-Nichols method, which shows really good results in benchmarks (Geekbench and GFXbench on hikey960 Android). The improved performance in Geekbench is ~10% (vs. old IPA). The main question from our side is the sysfs interface which we could be used to trigger this algorithm for better coefficients estimations. We ask user to echo to some sysfs files in thermal zone and start his/her workload. This new IPA 'learns' the system utilization and reaction in temperature. After a few rounds, we get better fitted coefficients. If you need more background about the code or mechanisms, or tests, I'm sure Chetan is happy to provide you those. If you are interested in those analyses we can find a way to share a .html file with the results from LISA notebook. We are waiting for your decision regarding the design and user interface. Regards, Lukasz [1] https://lore.kernel.org/lkml/42360f0f-5d53-085b-536f-33df93b787ca@arm.com/