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Commit 70494e6b authored by Abhijeet Dharmapurikar's avatar Abhijeet Dharmapurikar
Browse files

sched/fair: correctly handle cpus with same energy costs 



When energy delta is same as the chosen cpu, the energy model simply
rejects the new cpu.

This is incorrect behaviour, because it ends up selecting the cpu it
visits first. It should break ties intelligently - fix it such that
it prefers cpu in a shallower idle state.

Implement this.

Change-Id: I82f39163e71037eca05ea52c69800a71b1fdcc27
Signed-off-by: default avatarAbhijeet Dharmapurikar <adharmap@codeaurora.org>
parent c208338e

kernel/sched/fair.c

+25 −0
Original line number Diff line number Diff line
@@ -7335,6 +7335,25 @@ static inline struct cpumask *find_rtg_target(struct task_struct *p) 
}

#endif



/* return true if cpu should be chosen over best_energy_cpu */

static inline bool select_cpu_same_energy(int cpu, int best_cpu, int prev_cpu)

{

	if (best_cpu == prev_cpu)

		return false;



	if (idle_cpu(best_cpu) && idle_get_state_idx(cpu_rq(best_cpu)) <= 0)

		return false; /* best_cpu is idle wfi or shallower */



	if (idle_cpu(cpu) && idle_get_state_idx(cpu_rq(cpu)) <= 0)

		return true; /* new cpu is idle wfi or shallower */



	/*

	 * If we are this far this must be a tie between a busy and deep idle,

	 * pick the busy.

	 */

	return idle_cpu(best_cpu);

}



static DEFINE_PER_CPU(cpumask_t, energy_cpus);



/*
@@ -7481,6 +7500,12 @@ static int find_energy_efficient_cpu(struct task_struct *p, int prev_cpu, int sy 
		if (cur_energy < best_energy) {

			best_energy = cur_energy;

			best_energy_cpu = cpu;

		} else if (cur_energy == best_energy) {

			if (select_cpu_same_energy(cpu, best_energy_cpu,

						prev_cpu)) {

				best_energy = cur_energy;

				best_energy_cpu = cpu;

			}

		}

	}

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