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Commit 2e13f308 authored by Chris Redpath's avatar Chris Redpath
Browse files

sched/fair: Add a backup_cpu to find_best_target 



Sometimes we find a target cpu but then we do not use it as
the energy_diff indicates that we would increase energy usage
or not save anything. To offer an additional option for those
cases, we return a second option which is what we would have
selected if the target CPU had not been found. This gives us
another chance to try to save some energy.

Change-Id: I42c4f20aba10e4cf65b51ac4153e2e00e534c8c7
Signed-off-by: default avatarChris Redpath <chris.redpath@arm.com>
Signed-off-by: default avatarPatrick Bellasi <patrick.bellasi@arm.com>
parent 6cb8fccc

kernel/sched/fair.c

+19 −7
Original line number Diff line number Diff line
@@ -6238,7 +6238,8 @@ static int start_cpu(bool boosted) 
	return boosted ? rd->max_cap_orig_cpu : rd->min_cap_orig_cpu;

}



static inline int find_best_target(struct task_struct *p, bool boosted, bool prefer_idle)

static inline int find_best_target(struct task_struct *p, int *backup_cpu,

				   bool boosted, bool prefer_idle)

{

	unsigned long best_idle_min_cap_orig = ULONG_MAX;

	unsigned long min_util = boosted_task_util(p);
@@ -6255,6 +6256,8 @@ static inline int find_best_target(struct task_struct *p, bool boosted, bool pre 
	int target_cpu = -1;

	int cpu, i;



	*backup_cpu = -1;



	schedstat_inc(p, se.statistics.nr_wakeups_fbt_attempts);

	schedstat_inc(this_rq(), eas_stats.fbt_attempts);
@@ -6489,6 +6492,10 @@ static inline int find_best_target(struct task_struct *p, bool boosted, bool pre 
		target_cpu = prefer_idle

			? best_active_cpu

			: best_idle_cpu;

	else

		*backup_cpu = prefer_idle

		? best_active_cpu

		: best_idle_cpu;



	trace_sched_find_best_target(p, prefer_idle, min_util, cpu,

				     best_idle_cpu, best_active_cpu,
@@ -6527,7 +6534,7 @@ static int wake_cap(struct task_struct *p, int cpu, int prev_cpu) 
static int select_energy_cpu_brute(struct task_struct *p, int prev_cpu, int sync)

{

	struct sched_domain *sd;

	int target_cpu = prev_cpu, tmp_target;

	int target_cpu = prev_cpu, tmp_target, tmp_backup;

	bool boosted, prefer_idle;



	schedstat_inc(p, se.statistics.nr_wakeups_secb_attempts);
@@ -6556,7 +6563,7 @@ static int select_energy_cpu_brute(struct task_struct *p, int prev_cpu, int sync 


	sd = rcu_dereference(per_cpu(sd_ea, prev_cpu));

	/* Find a cpu with sufficient capacity */

	tmp_target = find_best_target(p, boosted, prefer_idle);

	tmp_target = find_best_target(p, &tmp_backup, boosted, prefer_idle);



	if (!sd)

		goto unlock;
@@ -6585,11 +6592,16 @@ static int select_energy_cpu_brute(struct task_struct *p, int prev_cpu, int sync 
		}



		if (energy_diff(&eenv) >= 0) {

			/* No energy saving for target_cpu, try backup */

			target_cpu = tmp_backup;

			eenv.dst_cpu = target_cpu;

			if (tmp_backup < 0 || energy_diff(&eenv) >= 0) {

				schedstat_inc(p, se.statistics.nr_wakeups_secb_no_nrg_sav);

				schedstat_inc(this_rq(), eas_stats.secb_no_nrg_sav);

				target_cpu = prev_cpu;

				goto unlock;

			}

		}



		schedstat_inc(p, se.statistics.nr_wakeups_secb_nrg_sav);

		schedstat_inc(this_rq(), eas_stats.secb_nrg_sav);