On Thu, May 22, 2025 at 10:51 AM Russell Haley <yumpusamongus@xxxxxxxxx> wrote: > > > On 5/22/25 3:05 AM, Shashank Balaji wrote: > > The userspace governor does not have the CPUFREQ_GOV_STRICT_TARGET flag, which > > means the requested frequency may not strictly be followed. This is true in the > > case of the intel_pstate driver with HWP enabled. When programming the > > HWP_REQUEST MSR, the min_perf is set to `scaling_setspeed`, and the max_perf > > is set to the policy's max. So, the hardware is free to increase the frequency > > beyond the requested frequency. > > > > This behaviour can be slightly surprising, given the current wording "allows > > userspace to set the CPU frequency". Hence, document this. > > > > In my opinion, the documentation is correct, and it is the > implementation in intel_pstate that is wrong. If the user wanted two > separate knobs that control the minimum and maximum frequencies, they > could leave intel_pstate in "active" mode and change scaling_min_freq > and scaling_max_freq. > > If the user asks for the frequency to be set from userspace, the > frequency had damn well better be set from userspace. The userspace governor requests a frequency between policy->min and policy->max on behalf of user space. In intel_pstate this translates to setting DESIRED_PERF to the requested value which is also the case for the other governors. There is no guarantee that the request will be granted by the hardware, either way.
