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cpufreq: intel_pstate: Proportional algorithm for Atom

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The PID algorithm used by the intel_pstate driver tends to drive
performance to the minimum for workloads with utilization below the
setpoint, which is undesirable, so replace it with a modified
"proportional" algorithm on Atom.

The new algorithm will set the new P-state to be 1.25 times the
available maximum times the (frequency-invariant) utilization during
the previous sampling period except when the target P-state computed
this way is lower than the average P-state during the previous
sampling period.  In the latter case, it will increase the target by
50% of the difference between it and the average P-state to prevent
performance from dropping down too fast in some cases.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Tested-by: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
This commit is contained in:
Rafael J. Wysocki 2016-10-06 14:07:51 +02:00
parent f00593a4bd
commit 0843e83c1a
1 changed files with 21 additions and 1 deletions
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22
drivers/cpufreq/intel_pstate.c
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@ -1232,6 +1232,7 @@ static inline int32_t get_target_pstate_use_cpu_load(struct cpudata *cpu)
{
struct sample *sample = &cpu->sample;
int32_t busy_frac, boost;
int target, avg_pstate;
busy_frac = div_fp(sample->mperf, sample->tsc);
@ -1242,7 +1243,26 @@ static inline int32_t get_target_pstate_use_cpu_load(struct cpudata *cpu)
busy_frac = boost;
sample->busy_scaled = busy_frac * 100;
return get_avg_pstate(cpu) - pid_calc(&cpu->pid, sample->busy_scaled);
target = limits->no_turbo || limits->turbo_disabled ?
cpu->pstate.max_pstate : cpu->pstate.turbo_pstate;
target += target >> 2;
target = mul_fp(target, busy_frac);
if (target < cpu->pstate.min_pstate)
target = cpu->pstate.min_pstate;
/*
* If the average P-state during the previous cycle was higher than the
* current target, add 50% of the difference to the target to reduce
* possible performance oscillations and offset possible performance
* loss related to moving the workload from one CPU to another within
* a package/module.
*/
avg_pstate = get_avg_pstate(cpu);
if (avg_pstate > target)
target += (avg_pstate - target) >> 1;
return target;
}
static inline int32_t get_target_pstate_use_performance(struct cpudata *cpu)