dvfs tabel vs cpufreq-info discrepancy (opi-pc)

jock · April 17, 2016

Hello,

I was tweaking the dvfs table on my OrangePI PC to find the maximum efficiency sweet spot.

I noticed that no way I change the dvfs table, the maximum frequency is always 1296 Mhz.

This is the very simple dvfs table I'm using now:

[dvfs_table]
pmuic_type = 2
extremity_freq = 1200000000
max_freq = 1200000000
min_freq = 480000000
LV_count = 2
LV1_freq = 1200000000
LV1_volt = 1240
LV2_freq = 480000000
LV2_volt = 980

but this is the result of an excerpt cpufreq-info command for cpu0:

driver: cpufreq-sunxi
  CPUs which run at the same hardware frequency: 0 1 2 3
  CPUs which need to have their frequency coordinated by software: 0 1 2 3
  maximum transition latency: 2.00 ms.
  hardware limits: 480 MHz - 1.20 GHz
  available cpufreq governors: conservative, ondemand, userspace, powersave, interactive, performance
  current policy: frequency should be within 480 MHz and 1.30 GHz.
                  The governor "interactive" may decide which speed to use
                  within this range.
  current CPU frequency is 480 MHz.
  cpufreq stats: 60.0 MHz:0.00%, 120 MHz:0.00%, 240 MHz:0.00%, 312 MHz:0.00%, 408 MHz:0.00%, 480 MHz:72.35%, 504 MHz:0.00%, 600 MHz:0.03%, 648 MHz:0.02%, 720 MHz:0.00%, 816 MHz:0.00%, 912 MHz:0.00%, 1.01 GHz:1.66%, 1.10 GHz:0.07%, 1.20 GHz:1.52%, 1.30 GHz:24.33%, 1.34 GHz:0.00%, 1.44 GHz:0.00%, 1.54 GHz:0.00%  (64)

I don't understand why hardware limits are 480 Mhz - 1.2 Ghz but the CPU is allowed to do transitions up to 1.3 Ghz?

Benchmarks confirm the CPU is running at 1.3Ghz as maximum frequency. I removed the 1296 Mhz reference from cooler_table and adjust it too, but nothing changed. Is there something I'm missing?

tkaiser · April 17, 2016

Hmm... I would exchange 1200 with 1296 in dvfs_table and cooler table (unless you allow it there too no switching to higher frequencies will happen), adjust the value in /etc/default/cpufrequtils and try again. No idea what cpufreq-info is reporting since I always disable cpufrequtils when starting tests and when a board is in productive use I also don't use the tool (but Monitoring using SNMP or RPi-Monitor instead).

jock · April 17, 2016

Thanks for the hint, I changed /etc/default/cpufrequtils with a maximum frequency of 1200 Mhz.

Still I don't understand why cpufreq-info proposes all the frequency steps, as long as the sunxi driver should report the frequencies given in the dvfs table...

tkaiser · April 17, 2016

Still I don't understand why cpufreq-info proposes all the frequency steps, as long as the sunxi driver should report the frequencies given in the dvfs table...

Maybe looking into /sys/devices/system/cpu/cpu0/cpufreq/stats/ will answer this? One thing is which cpufreq operating points are defined in kernel sources, another which dvfs operating points are defined/allowed in cooler_table and also another how cpufrequtils configure the kernel through sysfs when installed and running.