RE: sched/cpufreq: Rework schedutil governor performance estimation - Regression bisected

[Doug Smythies]

Hi Vincent,
Thank you for your quick reply.

On 2024.02.09.14:11 Vincent wrote:
On Fri, 9 Feb 2024 at 22:38, Doug Smythies <dsmythies@xxxxxxxxx> wrote:
>>
>> Hi,
>>
>> I noticed a regression in the 6.8rc series kernels. Bisecting the kernel pointed to:
>>
>> # first bad commit: [9c0b4bb7f6303c9c4e2e34984c46f5a86478f84d]
>> sched/cpufreq: Rework schedutil governor performance estimation
>>
>> There was previous bisection and suggestion of reversion,
>> but I guess it wasn't done in the end. [1]
>
> This has been fixed with
> https://lore.kernel.org/all/170539970061.398.16662091173685476681.tip-bot2@tip-bot2/

Okay, thanks. I didn't find that one.

>> The regression: reduced maximum CPU frequency is ignored.

> This seems to be something new.
> schedutil doesn't impact the max_freq and it's up to cpufreq driver
> select the final freq which should stay within the limits

Okay. All I know is this is the commit that caused the regression.
I do not know why, but I do wonder if there could any relationship with
the old, never fixed, problem of incorrect stale frequencies reported
under the same operating conditions. See the V2 note:
https://lore.kernel.org/all/001d01d9d3a7$71736f50$545a4df0$@telus.net/

where I haven't been able to figure out a solution.

>> Conditions:
>> CPU frequency scaling driver: intel_cpufreq (a.k.a intel_pstate in passive mode)
>> CPU frequency scaling governor: schedutil
>> HWP (HardWare Pstate) control (a.k.a. Intel_speedshift): Enabled
>> Processor: Intel(R) Core(TM) i5-10600K CPU @ 4.10GHz
>>
>> I did not check any other conditions, i.e. HWP disabled or the acpi-cpufreq driver.
>>
>> Example: A 100% load on CPU 5.
>>
>> sudo turbostat --quiet --Summary --show Busy%,Bzy_MHz,IRQ,PkgWatt,PkgTmp,RAMWatt,GFXWatt,CorWatt --interval 15
>> Busy%   Bzy_MHz IRQ     PkgTmp  PkgWatt CorWatt GFXWatt RAMWatt
>> 8.42    4636    21823   67      28.40   27.56   0.00    2.59
>> 8.40    4577    17724   66      27.57   26.73   0.00    2.59
>> 8.35    4637    19535   66      28.65   27.81   0.00    2.60
>> 8.41    4578    20723   66      27.73   26.89   0.00    2.59
>> 8.40    4558    19156   67      27.39   26.55   0.00    2.58
>> 8.34    4502    18127   67      26.79   25.96   0.00    2.57
>>
>> grep . /sys/devices/system/cpu/cpu*/cpufreq/scaling_max_freq
>> /sys/devices/system/cpu/cpu0/cpufreq/scaling_max_freq:2400000
>> /sys/devices/system/cpu/cpu10/cpufreq/scaling_max_freq:2400000
>> /sys/devices/system/cpu/cpu11/cpufreq/scaling_max_freq:2400000
>> /sys/devices/system/cpu/cpu1/cpufreq/scaling_max_freq:2400000
>> /sys/devices/system/cpu/cpu2/cpufreq/scaling_max_freq:2400000
>> /sys/devices/system/cpu/cpu3/cpufreq/scaling_max_freq:2400000
>> /sys/devices/system/cpu/cpu4/cpufreq/scaling_max_freq:2400000
>> /sys/devices/system/cpu/cpu5/cpufreq/scaling_max_freq:2400000
>> /sys/devices/system/cpu/cpu6/cpufreq/scaling_max_freq:2400000
>> /sys/devices/system/cpu/cpu7/cpufreq/scaling_max_freq:2400000
>> /sys/devices/system/cpu/cpu8/cpufreq/scaling_max_freq:2400000
>> /sys/devices/system/cpu/cpu9/cpufreq/scaling_max_freq:2400000
>>
>> grep . /sys/devices/system/cpu/cpu5/cpufreq/*
>> /sys/devices/system/cpu/cpu5/cpufreq/affected_cpus:5
>> /sys/devices/system/cpu/cpu5/cpufreq/base_frequency:4100000
>> /sys/devices/system/cpu/cpu5/cpufreq/cpuinfo_max_freq:4800000
>> /sys/devices/system/cpu/cpu5/cpufreq/cpuinfo_min_freq:800000
>> /sys/devices/system/cpu/cpu5/cpufreq/cpuinfo_transition_latency:20000
>> /sys/devices/system/cpu/cpu5/cpufreq/energy_performance_available_preferences:default performance balance_performance balance_power
>> power
>> /sys/devices/system/cpu/cpu5/cpufreq/energy_performance_preference:balance_performance
>> /sys/devices/system/cpu/cpu5/cpufreq/related_cpus:5
>> /sys/devices/system/cpu/cpu5/cpufreq/scaling_available_governors:conservative ondemand userspace powersave performance schedutil
>> /sys/devices/system/cpu/cpu5/cpufreq/scaling_cur_freq:4799998
>> /sys/devices/system/cpu/cpu5/cpufreq/scaling_driver:intel_cpufreq
>> /sys/devices/system/cpu/cpu5/cpufreq/scaling_governor:schedutil
>> /sys/devices/system/cpu/cpu5/cpufreq/scaling_max_freq:2400000
>> /sys/devices/system/cpu/cpu5/cpufreq/scaling_min_freq:800000
>> /sys/devices/system/cpu/cpu5/cpufreq/scaling_setspeed:<unsupported>
>>
>> [1] https://lore.kernel.org/all/CAKfTPtDCQuJjpi6=zjeWPcLeP+ZY5Dw7XDrZ-LpXqEAAUbXLhA@xxxxxxxxxxxxxx/