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Commit b8bd1581 authored by Rafael J. Wysocki's avatar Rafael J. Wysocki
Browse files

cpufreq: intel_pstate: Rework iowait boosting to be less aggressive 



The current iowait boosting mechanism in intel_pstate_update_util()
is quite aggressive, as it goes to the maximum P-state right away,
and may cause excessive amounts of energy to be used, which is not
desirable and arguably isn't necessary too.

Follow commit a5a0809b ("cpufreq: schedutil: Make iowait boost
more energy efficient") that reworked the analogous iowait boost
mechanism in the schedutil governor and make the iowait boosting
in intel_pstate_update_util() work along the same lines.

Signed-off-by: default avatarRafael J. Wysocki <rafael.j.wysocki@intel.com>
parent a8e1942d

drivers/cpufreq/intel_pstate.c

+18 −18
Original line number Diff line number Diff line
@@ -50,6 +50,8 @@ 
#define int_tofp(X) ((int64_t)(X) << FRAC_BITS)

#define fp_toint(X) ((X) >> FRAC_BITS)



#define ONE_EIGHTH_FP ((int64_t)1 << (FRAC_BITS - 3))



#define EXT_BITS 6

#define EXT_FRAC_BITS (EXT_BITS + FRAC_BITS)

#define fp_ext_toint(X) ((X) >> EXT_FRAC_BITS)
@@ -1671,17 +1673,14 @@ static inline int32_t get_avg_pstate(struct cpudata *cpu) 
static inline int32_t get_target_pstate(struct cpudata *cpu)

{

	struct sample *sample = &cpu->sample;

	int32_t busy_frac, boost;

	int32_t busy_frac;

	int target, avg_pstate;



	busy_frac = div_fp(sample->mperf << cpu->aperf_mperf_shift,

			   sample->tsc);



	boost = cpu->iowait_boost;

	cpu->iowait_boost >>= 1;



	if (busy_frac < boost)

		busy_frac = boost;

	if (busy_frac < cpu->iowait_boost)

		busy_frac = cpu->iowait_boost;



	sample->busy_scaled = busy_frac * 100;
@@ -1758,29 +1757,30 @@ static void intel_pstate_update_util(struct update_util_data *data, u64 time, 
	if (smp_processor_id() != cpu->cpu)

		return;



	delta_ns = time - cpu->last_update;

	if (flags & SCHED_CPUFREQ_IOWAIT) {

		/* Start over if the CPU may have been idle. */

		if (delta_ns > TICK_NSEC) {

			cpu->iowait_boost = ONE_EIGHTH_FP;

		} else if (cpu->iowait_boost) {

			cpu->iowait_boost <<= 1;

			if (cpu->iowait_boost > int_tofp(1))

				cpu->iowait_boost = int_tofp(1);

		cpu->last_update = time;

		/*

		 * The last time the busy was 100% so P-state was max anyway

		 * so avoid overhead of computation.

		 */

		if (fp_toint(cpu->sample.busy_scaled) == 100)

			return;



		goto set_pstate;

		} else {

			cpu->iowait_boost = ONE_EIGHTH_FP;

		}

	} else if (cpu->iowait_boost) {

		/* Clear iowait_boost if the CPU may have been idle. */

		delta_ns = time - cpu->last_update;

		if (delta_ns > TICK_NSEC)

			cpu->iowait_boost = 0;

		else

			cpu->iowait_boost >>= 1;

	}

	cpu->last_update = time;

	delta_ns = time - cpu->sample.time;

	if ((s64)delta_ns < INTEL_PSTATE_SAMPLING_INTERVAL)

		return;



set_pstate:

	if (intel_pstate_sample(cpu, time))

		intel_pstate_adjust_pstate(cpu);

}