Messages in this thread | | | Date | Thu, 12 Nov 2020 15:11:23 +0530 | From | Viresh Kumar <> | Subject | Re: [PATCH V2 2/2] thermal: cpufreq_cooling: Reuse sched_cpu_util() |
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On 23-10-20, 12:37, Peter Zijlstra wrote: > Actual numbers that show the goodness would be nice ;-) Because clearly > we're doing this make it better.
Hi Peter,
I tried the patchset with hackbench, sysbench and schbench. None of them showed any regression or significant improvements. schbench was the one I was most hopeful with as it creates the scenario where the utilization numbers provide a better estimate of the future.
Scenario 1: The CPUs were mostly idle in the previous polling window of the IPA governor as the tasks were sleeping and here are the details from traces (load is in %):
thermal_power_cpu_get_power: Old: cpus=00000000,000000ff freq=1200000 total_load=203 load={{0x35,0x1,0x0,0x31,0x0,0x0,0x64,0x0}} dynamic_power=1339 thermal_power_cpu_get_power: New: cpus=00000000,000000ff freq=1200000 total_load=600 load={{0x60,0x46,0x45,0x45,0x48,0x3b,0x61,0x44}} dynamic_power=3960
Here, the "Old" line gives the load and requested_power (dynamic_power here) numbers calculated using the idle time based implementation. And "New" is based on CPU utilization from this patchset.
As can be clearly seen, the load and requested_power numbers are simply incorrect in the idle time based approach and the numbers collected from CPU's utilization are much better and will also match the expectations of the schedutil governor.
Scenario 2: The CPUs were busy in the previous polling window of the IPA governor:
thermal_power_cpu_get_power: Old: cpus=00000000,000000ff freq=1200000 total_load=800 load={{0x64,0x64,0x64,0x64,0x64,0x64,0x64,0x64}} dynamic_power=5280 thermal_power_cpu_get_power: New: cpus=00000000,000000ff freq=1200000 total_load=708 load={{0x4d,0x5c,0x5c,0x5b,0x5c,0x5c,0x51,0x5b}} dynamic_power=4672
As can be seen, the idle time based load is 100% for all the CPUs as it took only the last window into account, but in reality the CPUs aren't that loaded as shown by the utilazation numbers.
Though this patchset improves the power estimation done by the cpufreq_cooling driver (which matches with the freq scaling governor, schedutil, as well), the IPA governor doesn't necessarily appreciate the correctness of it as it takes the decision to choose the next cooling state based on multiple factors, like current temperature, target temperature, requested_power, all power players (who request power from it), etc. The algorithm is complex there and I am afraid the improved numbers here don't necessarily translate to better numbers for the benchmarks like schbench. Another factor can be IPAs tuning for my platform (Hikey6220).
Irrespective of the IPA governor, the estimate provided by the cpufreq cooling driver does improve a lot with this patchset and are better aligned with the schedutil governor and I believe it would be better to merge this nevertheless.
I have already prepared the next version which takes care of !SMP case, was just holding it off until I was trying to get some numbers out.
-- viresh
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