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[71.255.246.27]) by smtp.gmail.com with ESMTPSA id k40sm2523832qta.76.2019.10.31.09.52.14 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 31 Oct 2019 09:52:15 -0700 (PDT) Subject: Re: [Patch v4 0/6] Introduce Thermal Pressure To: Ionela Voinescu References: <1571776465-29763-1-git-send-email-thara.gopinath@linaro.org> <20191031094420.GA19197@e108754-lin> <5DBB0EB0.9050106@linaro.org> Cc: mingo@redhat.com, peterz@infradead.org, vincent.guittot@linaro.org, rui.zhang@intel.com, edubezval@gmail.com, qperret@google.com, linux-kernel@vger.kernel.org, amit.kachhap@gmail.com, javi.merino@kernel.org, daniel.lezcano@linaro.org From: Thara Gopinath Message-ID: <5DBB113E.8080804@linaro.org> Date: Thu, 31 Oct 2019 12:52:14 -0400 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.5.1 MIME-Version: 1.0 In-Reply-To: <5DBB0EB0.9050106@linaro.org> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 10/31/2019 12:41 PM, Thara Gopinath wrote: > On 10/31/2019 05:44 AM, Ionela Voinescu wrote: >> Hi Thara, >> >> On Tuesday 22 Oct 2019 at 16:34:19 (-0400), Thara Gopinath wrote: >>> Thermal governors can respond to an overheat event of a cpu by >>> capping the cpu's maximum possible frequency. This in turn >>> means that the maximum available compute capacity of the >>> cpu is restricted. But today in the kernel, task scheduler is >>> not notified of capping of maximum frequency of a cpu. >>> In other words, scheduler is unware of maximum capacity >> >> Nit: s/unware/unaware >> >>> restrictions placed on a cpu due to thermal activity. >>> This patch series attempts to address this issue. >>> The benefits identified are better task placement among available >>> cpus in event of overheating which in turn leads to better >>> performance numbers. >>> >>> The reduction in the maximum possible capacity of a cpu due to a >>> thermal event can be considered as thermal pressure. Instantaneous >>> thermal pressure is hard to record and can sometime be erroneous >>> as there can be mismatch between the actual capping of capacity >>> and scheduler recording it. Thus solution is to have a weighted >>> average per cpu value for thermal pressure over time. >>> The weight reflects the amount of time the cpu has spent at a >>> capped maximum frequency. Since thermal pressure is recorded as >>> an average, it must be decayed periodically. Exisiting algorithm >>> in the kernel scheduler pelt framework is re-used to calculate >>> the weighted average. This patch series also defines a sysctl >>> inerface to allow for a configurable decay period. >>> >>> Regarding testing, basic build, boot and sanity testing have been >>> performed on db845c platform with debian file system. >>> Further, dhrystone and hackbench tests have been >>> run with the thermal pressure algorithm. During testing, due to >>> constraints of step wise governor in dealing with big little systems, >>> trip point 0 temperature was made assymetric between cpus in little >>> cluster and big cluster; the idea being that >>> big core will heat up and cpu cooling device will throttle the >>> frequency of the big cores faster, there by limiting the maximum available >>> capacity and the scheduler will spread out tasks to little cores as well. >>> >> >> Can you please share the changes you've made to sdm845.dtsi and a kernel >> base on top of which to apply your patches? I would like to reproduce >> your results and run more tests and it would be good if our setups were >> as close as possible. > Hi Ionela > Thank you for the review. > So I tested this on 5.4-rc1 kernel. The dtsi changes is to reduce the > thermal trip points for the big CPUs to 60000 or 70000 from the default > 90000. I did this for 2 reasons > 1. I could never get the db845 to heat up sufficiently for my test cases > with the default trip. > 2. I was using the default step-wise governor for thermal. I did not > want little and big to start throttling by the same % because then the > task placement ratio will remain the same between little and big cores. > So I am not sure though if this is the set up under which Daniel ran glbench . I will let him comment on it. > > > -- Warm Regards Thara