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[71.255.246.27]) by smtp.gmail.com with ESMTPSA id u7sm2081788qkm.127.2019.10.31.09.41.21 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 31 Oct 2019 09:41:21 -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> 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: <5DBB0EB0.9050106@linaro.org> Date: Thu, 31 Oct 2019 12:41:20 -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: <20191031094420.GA19197@e108754-lin> 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 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. > >> Test Results >> >> Hackbench: 1 group , 30000 loops, 10 runs >> Result SD >> (Secs) (% of mean) >> No Thermal Pressure 14.03 2.69% >> Thermal Pressure PELT Algo. Decay : 32 ms 13.29 0.56% >> Thermal Pressure PELT Algo. Decay : 64 ms 12.57 1.56% >> Thermal Pressure PELT Algo. Decay : 128 ms 12.71 1.04% >> Thermal Pressure PELT Algo. Decay : 256 ms 12.29 1.42% >> Thermal Pressure PELT Algo. Decay : 512 ms 12.42 1.15% >> >> Dhrystone Run Time : 20 threads, 3000 MLOOPS >> Result SD >> (Secs) (% of mean) >> No Thermal Pressure 9.452 4.49% >> Thermal Pressure PELT Algo. Decay : 32 ms 8.793 5.30% >> Thermal Pressure PELT Algo. Decay : 64 ms 8.981 5.29% >> Thermal Pressure PELT Algo. Decay : 128 ms 8.647 6.62% >> Thermal Pressure PELT Algo. Decay : 256 ms 8.774 6.45% >> Thermal Pressure PELT Algo. Decay : 512 ms 8.603 5.41% >> > > Do you happen to know by how much the CPUs were capped during these > experiments? I don't have any captured results here. I know that big cores were capped and at times there was capacity inversion. Also I will fix the nit comments above. > > Thanks, > Ionela. > -- Warm Regards Thara