Commit d619b5cc authored by Rafael J. Wysocki's avatar Rafael J. Wysocki
Browse files

cpuidle: teo: Simplify counting events used for tick management 



Replace the tick_hits metric with a new tick_intercepts one that can be
used directly when deciding whether or not to stop the scheduler tick
and update the governor functional description accordingly.

No intentional functional impact.

Signed-off-by: default avatarRafael J. Wysocki <rafael.j.wysocki@intel.com>
Reviewed-by: default avatarChristian Loehle <christian.loehle@arm.com>
Tested-by: default avatarAboorva Devarajan <aboorvad@linux.ibm.com>
Tested-by: default avatarChristian Loehle <christian.loehle@arm.com>
Link: https://patch.msgid.link/1987985.PYKUYFuaPT@rjwysocki.net
parent e24f8a55

drivers/cpuidle/governors/teo.c

+14 −35
Original line number Diff line number Diff line
@@ -41,11 +41,7 @@ 
 * idle state 2, the third bin spans from the target residency of idle state 2

 * up to, but not including, the target residency of idle state 3 and so on.

 * The last bin spans from the target residency of the deepest idle state

 * supplied by the driver to the scheduler tick period length or to infinity if

 * the tick period length is less than the target residency of that state.  In

 * the latter case, the governor also counts events with the measured idle

 * duration between the tick period length and the target residency of the

 * deepest idle state.

 * supplied by the driver to infinity.

 *

 * Two metrics called "hits" and "intercepts" are associated with each bin.

 * They are updated every time before selecting an idle state for the given CPU
@@ -60,6 +56,10 @@ 
 * into by the sleep length (these events are also referred to as "intercepts"

 * below).

 *

 * The governor also counts "intercepts" with the measured idle duration below

 * the tick period length and uses this information when deciding whether or not

 * to stop the scheduler tick.

 *

 * In order to select an idle state for a CPU, the governor takes the following

 * steps (modulo the possible latency constraint that must be taken into account

 * too):
@@ -128,14 +128,14 @@ struct teo_bin { 
 * @sleep_length_ns: Time till the closest timer event (at the selection time).

 * @state_bins: Idle state data bins for this CPU.

 * @total: Grand total of the "intercepts" and "hits" metrics for all bins.

 * @tick_hits: Number of "hits" after TICK_NSEC.

 * @tick_intercepts: "Intercepts" before TICK_NSEC.

 */

struct teo_cpu {

	s64 time_span_ns;

	s64 sleep_length_ns;

	struct teo_bin state_bins[CPUIDLE_STATE_MAX];

	unsigned int total;

	unsigned int tick_hits;

	unsigned int tick_intercepts;

};



static DEFINE_PER_CPU(struct teo_cpu, teo_cpus);
@@ -207,38 +207,21 @@ static void teo_update(struct cpuidle_driver *drv, struct cpuidle_device *dev) 
		}

	}



	/*

	 * If the deepest state's target residency is below the tick length,

	 * make a record of it to help teo_select() decide whether or not

	 * to stop the tick.  This effectively adds an extra hits-only bin

	 * beyond the last state-related one.

	 */

	if (target_residency_ns < TICK_NSEC) {

		cpu_data->tick_hits -= cpu_data->tick_hits >> DECAY_SHIFT;



		cpu_data->total += cpu_data->tick_hits;



		if (TICK_NSEC <= cpu_data->sleep_length_ns) {

			idx_timer = drv->state_count;

			if (TICK_NSEC <= measured_ns) {

				cpu_data->tick_hits += PULSE;

				goto end;

			}

		}

	}



	cpu_data->tick_intercepts -= cpu_data->tick_intercepts >> DECAY_SHIFT;

	/*

	 * If the measured idle duration falls into the same bin as the sleep

	 * length, this is a "hit", so update the "hits" metric for that bin.

	 * Otherwise, update the "intercepts" metric for the bin fallen into by

	 * the measured idle duration.

	 */

	if (idx_timer == idx_duration)

	if (idx_timer == idx_duration) {

		cpu_data->state_bins[idx_timer].hits += PULSE;

	else

	} else {

		cpu_data->state_bins[idx_duration].intercepts += PULSE;

		if (TICK_NSEC <= measured_ns)

			cpu_data->tick_intercepts += PULSE;

	}



end:

	cpu_data->total += PULSE;

}
@@ -286,7 +269,6 @@ static int teo_select(struct cpuidle_driver *drv, struct cpuidle_device *dev, 
	struct teo_cpu *cpu_data = per_cpu_ptr(&teo_cpus, dev->cpu);

	s64 latency_req = cpuidle_governor_latency_req(dev->cpu);

	ktime_t delta_tick = TICK_NSEC / 2;

	unsigned int tick_intercept_sum = 0;

	unsigned int idx_intercept_sum = 0;

	unsigned int intercept_sum = 0;

	unsigned int idx_hit_sum = 0;
@@ -365,9 +347,6 @@ static int teo_select(struct cpuidle_driver *drv, struct cpuidle_device *dev, 
		goto end;

	}



	tick_intercept_sum = intercept_sum +

			cpu_data->state_bins[drv->state_count-1].intercepts;



	/*

	 * If the sum of the intercepts metric for all of the idle states

	 * shallower than the current candidate one (idx) is greater than the
@@ -477,7 +456,7 @@ static int teo_select(struct cpuidle_driver *drv, struct cpuidle_device *dev, 
	 * total wakeup events, do not stop the tick.

	 */

	if (drv->states[idx].target_residency_ns < TICK_NSEC &&

	    tick_intercept_sum > cpu_data->total / 2 + cpu_data->total / 8)

	    cpu_data->tick_intercepts > cpu_data->total / 2 + cpu_data->total / 8)

		duration_ns = TICK_NSEC / 2;



end: