Commit 8d4c97c1 authored by Pierre Gondois's avatar Pierre Gondois Committed by Peter Zijlstra
Browse files

sched/fair: Only compute base_energy_pd if necessary 



find_energy_efficient_cpu() searches the best energy CPU
to place a task on. To do so, the energy of each performance domain
(pd) is computed w/ and w/o the task placed on it.

The energy of a pd w/o the task (base_energy_pd) is computed prior
knowing whether a CPU is available in the pd.

Move the base_energy_pd computation after looping through the CPUs
of a pd and only compute it if at least one CPU is available.

Suggested-by: default avatarXuewen Yan <xuewen.yan@unisoc.com>
Signed-off-by: default avatarPierre Gondois <Pierre.Gondois@arm.com>
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: default avatarLukasz Luba <lukasz.luba@arm.com>
Reviewed-by: default avatarDietmar Eggemann <dietmar.eggemann@arm.com>
Reviewed-by: default avatarVincent Donnefort <vincent.donnefort@arm.com>
Link: https://lkml.kernel.org/r/20210504090743.9688-2-Pierre.Gondois@arm.com
parent e5e678e4

kernel/sched/fair.c

+24 −17
Original line number Diff line number Diff line
@@ -6687,13 +6687,10 @@ static int find_energy_efficient_cpu(struct task_struct *p, int prev_cpu) 


	for (; pd; pd = pd->next) {

		unsigned long cur_delta, spare_cap, max_spare_cap = 0;

		bool compute_prev_delta = false;

		unsigned long base_energy_pd;

		int max_spare_cap_cpu = -1;



		/* Compute the 'base' energy of the pd, without @p */

		base_energy_pd = compute_energy(p, -1, pd);

		base_energy += base_energy_pd;



		for_each_cpu_and(cpu, perf_domain_span(pd), sched_domain_span(sd)) {

			if (!cpumask_test_cpu(cpu, p->cpus_ptr))

				continue;
@@ -6714,25 +6711,35 @@ static int find_energy_efficient_cpu(struct task_struct *p, int prev_cpu) 
			if (!fits_capacity(util, cpu_cap))

				continue;



			/* Always use prev_cpu as a candidate. */

			if (cpu == prev_cpu) {

				prev_delta = compute_energy(p, prev_cpu, pd);

				prev_delta -= base_energy_pd;

				best_delta = min(best_delta, prev_delta);

			}



				/* Always use prev_cpu as a candidate. */

				compute_prev_delta = true;

			} else if (spare_cap > max_spare_cap) {

				/*

			 * Find the CPU with the maximum spare capacity in

			 * the performance domain

				 * Find the CPU with the maximum spare capacity

				 * in the performance domain.

				 */

			if (spare_cap > max_spare_cap) {

				max_spare_cap = spare_cap;

				max_spare_cap_cpu = cpu;

			}

		}



		/* Evaluate the energy impact of using this CPU. */

		if (max_spare_cap_cpu >= 0 && max_spare_cap_cpu != prev_cpu) {

		if (max_spare_cap_cpu < 0 && !compute_prev_delta)

			continue;



		/* Compute the 'base' energy of the pd, without @p */

		base_energy_pd = compute_energy(p, -1, pd);

		base_energy += base_energy_pd;



		/* Evaluate the energy impact of using prev_cpu. */

		if (compute_prev_delta) {

			prev_delta = compute_energy(p, prev_cpu, pd);

			prev_delta -= base_energy_pd;

			best_delta = min(best_delta, prev_delta);

		}



		/* Evaluate the energy impact of using max_spare_cap_cpu. */

		if (max_spare_cap_cpu >= 0) {

			cur_delta = compute_energy(p, max_spare_cap_cpu, pd);

			cur_delta -= base_energy_pd;

			if (cur_delta < best_delta) {