sched/fair: refactor find_best_target() for simplicity

Simplify backup_capacity handling and use 'unsigned long'
data type for cpu capacity, simplify target_util handling,
simplify idle_idx handling & refactor min_util, new_util.

Also return first idle cpu for prefer_idle task immediately.

Change-Id: Ic89e140f7b369f3965703fdc8463013d16e9b94a
Signed-off-by: Dietmar Eggemann <dietmar.eggemann@arm.com>
Signed-off-by: Chris Redpath <chris.redpath@arm.com>

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index d9c732de3295f91107518d30bf715474ff01b19b..270091323ae8af6cb543a3b6610bb9bcf215a923 100644 (file)
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -5756,13 +5756,12 @@ static int start_cpu(bool boosted)
 static inline int find_best_target(struct task_struct *p, bool boosted, bool prefer_idle)
 {
        int target_cpu = -1;
-       int target_util = 0;
-       int backup_capacity = 0;
+       unsigned long target_util = prefer_idle ? ULONG_MAX : 0;
+       unsigned long backup_capacity = ULONG_MAX;
        int best_idle_cpu = -1;
        int best_idle_cstate = INT_MAX;
        int backup_cpu = -1;
-       unsigned long min_util;
-       unsigned long new_util;
+       unsigned long min_util = boosted_task_util(p);
        struct sched_domain *sd;
        struct sched_group *sg;
        int cpu = start_cpu(boosted);
@@ -5777,15 +5776,11 @@ static inline int find_best_target(struct task_struct *p, bool boosted, bool pre
 
        sg = sd->groups;
 
-       min_util = boosted_task_util(p);
-
        do {
                int i;
 
                for_each_cpu_and(i, tsk_cpus_allowed(p), sched_group_cpus(sg)) {
-                       int cur_capacity;
-                       struct rq *rq;
-                       int idle_idx;
+                       unsigned long cur_capacity, new_util;
 
                        if (!cpu_online(i))
                                continue;
@@ -5803,6 +5798,7 @@ static inline int find_best_target(struct task_struct *p, bool boosted, bool pre
                         * than the one required to boost the task.
                         */
                        new_util = max(min_util, new_util);
+
                        if (new_util > capacity_orig_of(i))
                                continue;
 
@@ -5815,38 +5811,25 @@ static inline int find_best_target(struct task_struct *p, bool boosted, bool pre
                         * Unconditionally favoring tasks that prefer idle cpus to
                         * improve latency.
                         */
-                       if (idle_cpu(i) && prefer_idle) {
-                               if (best_idle_cpu < 0)
-                                       best_idle_cpu = i;
-                               continue;
-                       }
+                       if (idle_cpu(i) && prefer_idle)
+                               return i;
 
                        cur_capacity = capacity_curr_of(i);
-                       rq = cpu_rq(i);
-                       idle_idx = idle_get_state_idx(rq);
 
                        if (new_util < cur_capacity) {
                                if (cpu_rq(i)->nr_running) {
-                                       if (!prefer_idle) {
-                                               /* Find a target cpu with highest
-                                                * utilization.
-                                                */
-                                               if (target_util == 0 ||
-                                                       target_util < new_util) {
-                                                       target_cpu = i;
-                                                       target_util = new_util;
-                                               }
-                                       } else {
-                                               /* Find a target cpu with lowest
-                                                * utilization.
-                                                */
-                                               if (target_util == 0 ||
-                                                       target_util > new_util) {
-                                                       target_cpu = i;
-                                                       target_util = new_util;
-                                               }
+                                       /*
+                                        * Find a target cpu with the lowest/highest
+                                        * utilization if prefer_idle/!prefer_idle.
+                                        */
+                                       if ((prefer_idle && target_util > new_util) ||
+                                           (!prefer_idle && target_util < new_util)) {
+                                               target_util = new_util;
+                                               target_cpu = i;
                                        }
                                } else if (!prefer_idle) {
+                                       int idle_idx = idle_get_state_idx(cpu_rq(i));
+
                                        if (best_idle_cpu < 0 ||
                                                (sysctl_sched_cstate_aware &&
                                                        best_idle_cstate > idle_idx)) {
@@ -5854,18 +5837,15 @@ static inline int find_best_target(struct task_struct *p, bool boosted, bool pre
                                                best_idle_cpu = i;
                                        }
                                }
-                       } else if (backup_capacity == 0 ||
-                                       backup_capacity > cur_capacity) {
-                               // Find a backup cpu with least capacity.
+                       } else if (backup_capacity > cur_capacity) {
+                               /* Find a backup cpu with least capacity. */
                                backup_capacity = cur_capacity;
                                backup_cpu = i;
                        }
                }
        } while (sg = sg->next, sg != sd->groups);
 
-       if (prefer_idle && best_idle_cpu >= 0)
-               target_cpu = best_idle_cpu;
-       else if (target_cpu < 0)
+       if (target_cpu < 0)
                target_cpu = best_idle_cpu >= 0 ? best_idle_cpu : backup_cpu;
 
        return target_cpu;