zamnuts

I noticed that the ondemand sampling_rate was low in 5.x compared to 4.4's default. compare below:
 
$ uname -r 4.4.213-rk3399 $ sudo cat /sys/devices/system/cpu/cpufreq/policy{0,4}/ondemand/sampling_rate 40000 465000  
vs
 
$ uname -r 5.8.15-rockchip64 $ sudo cat /sys/devices/system/cpu/cpufreq/policy{0,4}/ondemand/sampling_rate 10000 10000  
It appears that 10000 seems to be a default (or the minimum value possible). Per https://www.kernel.org/doc/Documentation/cpu-freq/governors.txt 10000 is too low given the cpu_transition_latency:
$ uname -r 5.8.15-rockchip64 $ cat /sys/devices/system/cpu/cpu*/cpufreq/cpuinfo_transition_latency 40000 40000 40000 40000 515000 515000  
Given the documented formula cpuinfo_transition_latency * 750 / 1000, it should be (at a minimum) 30000 for cpu0-3, and 386250 for cpu4-5.
 
Using sysfs to configure cpufreq on boot with the revised sampling_rate seems to make it stable (although uptime is only about 2 days in). I ran periodic load testing to get the ondemand governor to change freq, and this config looks promising. Despite the previously mentioned calculations, i opted to align the sampling_rate with what was present in the 4.4 kernel:
$ tail -n+1 /etc/sysfs.d/* ==> /etc/sysfs.d/cpufreq-policy0.conf <== devices/system/cpu/cpufreq/policy0/scaling_governor = ondemand devices/system/cpu/cpufreq/policy0/scaling_max_freq = 1416000 devices/system/cpu/cpufreq/policy0/scaling_min_freq = 600000 devices/system/cpu/cpufreq/policy0/ondemand/sampling_rate = 40000 ==> /etc/sysfs.d/cpufreq-policy4.conf <== devices/system/cpu/cpufreq/policy4/scaling_governor = ondemand devices/system/cpu/cpufreq/policy4/scaling_max_freq = 1800000 devices/system/cpu/cpufreq/policy4/scaling_min_freq = 600000 devices/system/cpu/cpufreq/policy4/ondemand/sampling_rate = 465000 $ for i in 0 1 2 3 4 5; do sudo cat /sys/devices/system/cpu/cpu${i}/cpufreq/scaling_{governor,min_freq,max_freq}; done; ondemand 600000 1416000 ondemand 600000 1416000 ondemand 600000 1416000 ondemand 600000 1416000 ondemand 600000 1800000 ondemand 600000 1800000  
one of two boards are already crashing, not sure if its the board or what. going to switch to "performance" governor and see. figured i'd share the sample_rate delta info though.