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cpufreq: intel_pstate: Account for non C0 time
The current function to calculate cpu utilization uses the average P-state ratio (APerf/Mperf) scaled by the ratio of the current P-state to the max available non-turbo one. This leads to an overestimation of utilization which causes higher-performance P-states to be selected more often and that leads to increased energy consumption. This is a problem for low-power systems, so it is better to use a different utilization calculation algorithm for them. Namely, the Percent Busy value (or load) can be estimated as the ratio of the MPERF counter that runs at a constant rate only during active periods (C0) to the time stamp counter (TSC) that also runs (at the same rate) during idle. That is: Percent Busy = 100 * (delta_mperf / delta_tsc) Use this algorithm for platforms with SoCs based on the Airmont and Silvermont Atom cores. Signed-off-by: Philippe Longepe <philippe.longepe@intel.com> Signed-off-by: Stephane Gasparini <stephane.gasparini@intel.com> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
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157386b6fc
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1 changed files with 24 additions and 5 deletions
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@ -143,6 +143,7 @@ struct cpu_defaults {
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};
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static inline int32_t get_target_pstate_use_performance(struct cpudata *cpu);
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static inline int32_t get_target_pstate_use_cpu_load(struct cpudata *cpu);
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static struct pstate_adjust_policy pid_params;
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static struct pstate_funcs pstate_funcs;
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@ -763,7 +764,7 @@ static struct cpu_defaults silvermont_params = {
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.set = atom_set_pstate,
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.get_scaling = silvermont_get_scaling,
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.get_vid = atom_get_vid,
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.get_target_pstate = get_target_pstate_use_performance,
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.get_target_pstate = get_target_pstate_use_cpu_load,
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},
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};
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@ -784,7 +785,7 @@ static struct cpu_defaults airmont_params = {
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.set = atom_set_pstate,
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.get_scaling = airmont_get_scaling,
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.get_vid = atom_get_vid,
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.get_target_pstate = get_target_pstate_use_performance,
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.get_target_pstate = get_target_pstate_use_cpu_load,
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},
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};
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@ -890,12 +891,11 @@ static inline void intel_pstate_sample(struct cpudata *cpu)
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local_irq_save(flags);
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rdmsrl(MSR_IA32_APERF, aperf);
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rdmsrl(MSR_IA32_MPERF, mperf);
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if (cpu->prev_mperf == mperf) {
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tsc = rdtsc();
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if ((cpu->prev_mperf == mperf) || (cpu->prev_tsc == tsc)) {
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local_irq_restore(flags);
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return;
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}
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tsc = rdtsc();
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local_irq_restore(flags);
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cpu->last_sample_time = cpu->sample.time;
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@ -930,6 +930,25 @@ static inline void intel_pstate_set_sample_time(struct cpudata *cpu)
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mod_timer_pinned(&cpu->timer, jiffies + delay);
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}
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static inline int32_t get_target_pstate_use_cpu_load(struct cpudata *cpu)
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{
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struct sample *sample = &cpu->sample;
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int32_t cpu_load;
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/*
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* The load can be estimated as the ratio of the mperf counter
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* running at a constant frequency during active periods
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* (C0) and the time stamp counter running at the same frequency
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* also during C-states.
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*/
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cpu_load = div64_u64(int_tofp(100) * sample->mperf, sample->tsc);
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cpu->sample.busy_scaled = cpu_load;
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return cpu->pstate.current_pstate - pid_calc(&cpu->pid, cpu_load);
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}
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static inline int32_t get_target_pstate_use_performance(struct cpudata *cpu)
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{
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int32_t core_busy, max_pstate, current_pstate, sample_ratio;
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