On 5/22/25 4:47 AM, Rafael J. Wysocki wrote: > 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. Huh. On this Skylake box with kernel 6.14.6, it seems to be setting Minimum_Performance, and leaving desired at 0. > echo userspace | sudo tee /sys/devices/system/cpu/cpu*/cpufreq/scaling_governor userspace > echo 1400000 | sudo tee /sys/devices/system/cpu/cpu*/cpufreq/scaling_setspeed 1400000 > sudo x86_energy_perf_policy &| grep REQ cpu0: HWP_REQ: min 14 max 40 des 0 epp 128 window 0x0 (0*10^0us) use_pkg 0 cpu1: HWP_REQ: min 14 max 40 des 0 epp 128 window 0x0 (0*10^0us) use_pkg 0 cpu2: HWP_REQ: min 14 max 40 des 0 epp 128 window 0x0 (0*10^0us) use_pkg 0 cpu3: HWP_REQ: min 14 max 40 des 0 epp 128 window 0x0 (0*10^0us) use_pkg 0 cpu4: HWP_REQ: min 14 max 40 des 0 epp 128 window 0x0 (0*10^0us) use_pkg 0 cpu5: HWP_REQ: min 14 max 40 des 0 epp 128 window 0x0 (0*10^0us) use_pkg 0 cpu6: HWP_REQ: min 14 max 40 des 0 epp 128 window 0x0 (0*10^0us) use_pkg 0 cpu7: HWP_REQ: min 14 max 40 des 0 epp 128 window 0x0 (0*10^0us) use_pkg 0 Cheers, Russell
