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author | 2015-12-04 17:40:32 +0100 | |
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committer | 2015-12-10 01:17:40 +0100 | |
commit | e70eed2b64545ab5c9d2f4d43372d79762f1b985 (patch) | |
tree | dd00eb9d051a1ee5ba0bedd474cc1c085278ab31 /drivers/cpufreq | |
parent | cpufreq: intel_pstate: Configurable algorithm to get target pstate (diff) | |
download | linux-e70eed2b64545ab5c9d2f4d43372d79762f1b985.tar.gz linux-e70eed2b64545ab5c9d2f4d43372d79762f1b985.tar.bz2 linux-e70eed2b64545ab5c9d2f4d43372d79762f1b985.zip |
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>
Diffstat (limited to 'drivers/cpufreq')
-rw-r--r-- | drivers/cpufreq/intel_pstate.c | 29 |
1 files changed, 24 insertions, 5 deletions
diff --git a/drivers/cpufreq/intel_pstate.c b/drivers/cpufreq/intel_pstate.c index ff58029a56e2..8bfebaeda2dd 100644 --- a/drivers/cpufreq/intel_pstate.c +++ b/drivers/cpufreq/intel_pstate.c @@ -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; |