Messages in this thread | | | Subject | Re: [Patch v9 0/8] Introduce Thermal Pressure | From | Dietmar Eggemann <> | Date | Mon, 10 Feb 2020 13:07:19 +0100 |
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On 28/01/2020 23:35, 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 unaware 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%
What do we do on systems on which one Frequency domain spawns all the CPUs (e.g. Hikey620)?
perf stat --null --repeat 10 -- perf bench sched messaging -g 10 -l 1000
# Running 'sched/messaging' benchmark: # 20 sender and receiver processes per group # 10 groups == 400 processes run
Total time: 4.697 [sec] # Running 'sched/messaging' benchmark: [ 8082.882751] hisi_thermal f7030700.tsensor: sensor <2> THERMAL ALARM: 66385 > 65000 # 20 sender and receiver processes per group # 10 groups == 400 processes run
Total time: 4.910 [sec] # Running 'sched/messaging' benchmark: [ 8091.070386] CPU3 cpus=0-7 th_pressure=205 [ 8091.178390] CPU3 cpus=0-7 th_pressure=0 [ 8091.286389] CPU3 cpus=0-7 th_pressure=205 [ 8091.398397] CPU3 cpus=0-7 th_pressure=0
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