amd-pstate: Setting the maximum frequency in guided mode

Siddh Raman Pant sanganaka at
Tue Aug 15 09:14:56 EDT 2023


I am trying out the amd-pstate guided mode. If I understand the docs
correctly [1], guided mode essentially enforces a range (min, max)
over the frequency which can be selected by the processor, i.e. it is
like active mode but with range enforced.

If true, it looks attractive for battery saving. So on battery, I'd
like to use conservative governor with a max frequency of, say, 1.8
GHz, just as a test.

So after setting the maximum scaling frequency to 1.8 GHz using
TLP (which now supports amd-pstate [2]), `$ cpupower frequency-info`
yielded the following:

analyzing CPU 7:
  driver: amd-pstate
  CPUs which run at the same hardware frequency: 7
  CPUs which need to have their frequency coordinated by software: 7
  maximum transition latency: 20.0 us
  hardware limits: 400 MHz - 2.10 GHz
  available cpufreq governors: userspace powersave ondemand conservative performance schedutil
  current policy: frequency should be within 400 MHz and 1.80 GHz.
                  The governor "conservative" may decide which speed to use
                  within this range.
  current CPU frequency: Unable to call hardware
  current CPU frequency: 2.75 GHz (asserted by call to kernel)
  boost state support:
    Supported: yes
    Active: no
    AMD PSTATE Highest Performance: 255. Maximum Frequency: 4.06 GHz.
    AMD PSTATE Nominal Performance: 132. Nominal Frequency: 2.10 GHz.
    AMD PSTATE Lowest Non-linear Performance: 70. Lowest Non-linear Frequency: 1.11 GHz.
    AMD PSTATE Lowest Performance: 26. Lowest Frequency: 400 MHz.

Why is the frequency 2.75 GHz? Even the nominal max is 2.1 GHz, and
the output says boost is not active either. 



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