Messages in this thread Patch in this message |  | | From | "Rafael J. Wysocki" <> | Subject | [RFC/RFT][PATCH v2] cpufreq: intel_pstate: Proportional algorithm for Atom | Date | Wed, 05 Oct 2016 15:14:44 +0200 |
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From: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
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> ---
It is better to compare the average P-state to the target (than to compare the average perf ratio to the utilization), because that takes turbo into account more accurately.
Plus if the target is below the min, it is better to compare the min to the average instead of comparing the target to it.
--- drivers/cpufreq/intel_pstate.c | 22 +++++++++++++++++++++- 1 file changed, 21 insertions(+), 1 deletion(-)
Index: linux-pm/drivers/cpufreq/intel_pstate.c =================================================================== --- linux-pm.orig/drivers/cpufreq/intel_pstate.c +++ linux-pm/drivers/cpufreq/intel_pstate.c @@ -1232,6 +1232,7 @@ static inline int32_t get_target_pstate_ { 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_ 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)
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