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([2a01:e34:ed2f:f020:bc1d:8e1f:c99f:e225]) by smtp.googlemail.com with ESMTPSA id g5sm3976392wmg.12.2019.10.31.04.54.04 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 31 Oct 2019 04:54:05 -0700 (PDT) Subject: Re: [Patch v4 0/6] Introduce Thermal Pressure To: Ionela Voinescu Cc: Thara Gopinath , 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 References: <1571776465-29763-1-git-send-email-thara.gopinath@linaro.org> <20191031100631.GC19197@e108754-lin> From: Daniel Lezcano Openpgp: preference=signencrypt Autocrypt: addr=daniel.lezcano@linaro.org; prefer-encrypt=mutual; keydata= mQINBFv/yykBEADDdW8RZu7iZILSf3zxq5y8YdaeyZjI/MaqgnvG/c3WjFaunoTMspeusiFE sXvtg3ehTOoyD0oFjKkHaia1Zpa1m/gnNdT/WvTveLfGA1gH+yGes2Sr53Ht8hWYZFYMZc8V 2pbSKh8wepq4g8r5YI1XUy9YbcTdj5mVrTklyGWA49NOeJz2QbfytMT3DJmk40LqwK6CCSU0 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TQT1z7oGVFLQCpE5ALf8ybuta1yjf5Y6uJ2pVeSSj0BxnwCIzme7QXwCpgYqDTLu+QvYs4/y 6zzkvSnnsyohHW6AOchOVNjTHhFhFYn36TuV53laydaXK/zgo3NsOpATFObyK3N5lhb1G9tN Lrev/4WVxNr0LPXl9bdCbQGzIQK+kAPcg8u9f2MMhHQiQX8FAjhP3wtACRhfUz9RaQykxiwv y0s5uI05ZSXhqFs9iLlh3zNU1i6J1cdzA8BReoa3cKz4UiGKEffT857iMvT/ZmgSdYY57EgV UWm57SN2ok2Ii8AXlanH5SJPkbwJZhiB7kO0cjebmoA/1SA+5yTc3zEKKFuxcpfiXxt0d/OJ om6jCJ5/uKB5Cz9bJj0WdlvS2Xb11Jrs90MoVa74H5me4jOw7m9Yyg3qExOFOXUPFL6N Message-ID: <2009bac3-405a-c60e-a1dd-191625ff3fc5@linaro.org> Date: Thu, 31 Oct 2019 12:54:03 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.8.0 MIME-Version: 1.0 In-Reply-To: <20191031100631.GC19197@e108754-lin> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Ionela, On 31/10/2019 11:07, Ionela Voinescu wrote: > Hi Daniel, > > On Tuesday 29 Oct 2019 at 16:34:11 (+0100), Daniel Lezcano wrote: >> Hi Thara, >> >> On 22/10/2019 22:34, 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 >>> 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. >>> >>> 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% >> >> I took the opportunity to try glmark2 on the db845c platform with the >> default decay and got the following glmark2 scores: >> >> Without thermal pressure: >> >> # NumSamples = 9; Min = 790.00; Max = 805.00 >> # Mean = 794.888889; Variance = 19.209877; SD = 4.382907; Median 794.000000 >> # each ∎ represents a count of 1 >> 790.0000 - 791.5000 [ 2]: ∎∎ >> 791.5000 - 793.0000 [ 2]: ∎∎ >> 793.0000 - 794.5000 [ 2]: ∎∎ >> 794.5000 - 796.0000 [ 1]: ∎ >> 796.0000 - 797.5000 [ 0]: >> 797.5000 - 799.0000 [ 1]: ∎ >> 799.0000 - 800.5000 [ 0]: >> 800.5000 - 802.0000 [ 0]: >> 802.0000 - 803.5000 [ 0]: >> 803.5000 - 805.0000 [ 1]: ∎ >> >> >> With thermal pressure: >> >> # NumSamples = 9; Min = 933.00; Max = 960.00 >> # Mean = 940.777778; Variance = 64.172840; SD = 8.010795; Median 937.000000 >> # each ∎ represents a count of 1 >> 933.0000 - 935.7000 [ 3]: ∎∎∎ >> 935.7000 - 938.4000 [ 2]: ∎∎ >> 938.4000 - 941.1000 [ 2]: ∎∎ >> 941.1000 - 943.8000 [ 0]: >> 943.8000 - 946.5000 [ 0]: >> 946.5000 - 949.2000 [ 1]: ∎ >> 949.2000 - 951.9000 [ 0]: >> 951.9000 - 954.6000 [ 0]: >> 954.6000 - 957.3000 [ 0]: >> 957.3000 - 960.0000 [ 1]: ∎ >> > > Interesting! If I'm interpreting these correctly there seems to be > significant improvement when applying thermal pressure. > > I'm not familiar with glmark2, can you tell me more about the process > and the work that the benchmark does? glmark2 is a 3D benchmark. I ran it without parameters, so all tests are run. At the end, it gives a score which are the values given above. > I assume this is a GPU benchmark, > but not knowing more about it I fail to see the correlation between > applying thermal pressure to CPU capacities and the improvement of GPU > performance. > Do you happen to know more about the behaviour that resulted in these > benchmark scores? My hypothesis is glmark2 makes the GPU to contribute a lot to the heating effect, thus increasing the temperature to the CPU close to it. -- Linaro.org │ Open source software for ARM SoCs Follow Linaro: Facebook | Twitter | Blog