Messages in this thread | | | Subject | Re: [Patch v4 0/6] Introduce Thermal Pressure | From | Daniel Lezcano <> | Date | Tue, 29 Oct 2019 16:34:11 +0100 |
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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]: ∎
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