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cpufreq: intel_pstate: Account for non C0 time

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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>
This commit is contained in:
Philippe Longepe 2015-12-04 17:40:32 +01:00 committed by Rafael J. Wysocki
parent 157386b6fc
commit e70eed2b64
1 changed files with 24 additions and 5 deletions
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29
drivers/cpufreq/intel_pstate.c
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@ -143,6 +143,7 @@ struct cpu_defaults {
};
static inline int32_t get_target_pstate_use_performance(struct cpudata *cpu);
static inline int32_t get_target_pstate_use_cpu_load(struct cpudata *cpu);
static struct pstate_adjust_policy pid_params;
static struct pstate_funcs pstate_funcs;
@ -763,7 +764,7 @@ static struct cpu_defaults silvermont_params = {
.set = atom_set_pstate,
.get_scaling = silvermont_get_scaling,
.get_vid = atom_get_vid,
.get_target_pstate = get_target_pstate_use_performance,
.get_target_pstate = get_target_pstate_use_cpu_load,
},
};
@ -784,7 +785,7 @@ static struct cpu_defaults airmont_params = {
.set = atom_set_pstate,
.get_scaling = airmont_get_scaling,
.get_vid = atom_get_vid,
.get_target_pstate = get_target_pstate_use_performance,
.get_target_pstate = get_target_pstate_use_cpu_load,
},
};
@ -890,12 +891,11 @@ static inline void intel_pstate_sample(struct cpudata *cpu)
local_irq_save(flags);
rdmsrl(MSR_IA32_APERF, aperf);
rdmsrl(MSR_IA32_MPERF, mperf);
if (cpu->prev_mperf == mperf) {
tsc = rdtsc();
if ((cpu->prev_mperf == mperf) || (cpu->prev_tsc == tsc)) {
local_irq_restore(flags);
return;
}
tsc = rdtsc();
local_irq_restore(flags);
cpu->last_sample_time = cpu->sample.time;
@ -930,6 +930,25 @@ static inline void intel_pstate_set_sample_time(struct cpudata *cpu)
mod_timer_pinned(&cpu->timer, jiffies + delay);
}
static inline int32_t get_target_pstate_use_cpu_load(struct cpudata *cpu)
{
struct sample *sample = &cpu->sample;
int32_t cpu_load;
/*
* The load can be estimated as the ratio of the mperf counter
* running at a constant frequency during active periods
* (C0) and the time stamp counter running at the same frequency
* also during C-states.
*/
cpu_load = div64_u64(int_tofp(100) * sample->mperf, sample->tsc);
cpu->sample.busy_scaled = cpu_load;
return cpu->pstate.current_pstate - pid_calc(&cpu->pid, cpu_load);
}
static inline int32_t get_target_pstate_use_performance(struct cpudata *cpu)
{
int32_t core_busy, max_pstate, current_pstate, sample_ratio;