sched: mix tasks and groups

This patch allows tasks and groups to exist in the same cfs_rq. With this
change the CFS group scheduling follows a 1/(M+N) model from a 1/(1+N)
fairness model where M tasks and N groups exist at the cfs_rq level.

[a.p.zijlstra@chello.nl: rt bits and assorted fixes]
Signed-off-by: Dhaval Giani <dhaval@linux.vnet.ibm.com>
Signed-off-by: Srivatsa Vaddagiri <vatsa@linux.vnet.ibm.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 45 insertions, 6 deletions

diff --git a/kernel/sched_fair.c b/kernel/sched_fair.c
index 022e036f2c3..3dde0f0ec93 100644
--- a/kernel/sched_fair.c
+++ b/kernel/sched_fair.c
@@ -1133,6 +1133,17 @@ wakeup_preempt_entity(struct sched_entity *curr, struct sched_entity *se)
         return 0;
 }
 
+/* return depth at which a sched entity is present in the hierarchy */
+static inline int depth_se(struct sched_entity *se)
+{
+        int depth = 0;
+
+        for_each_sched_entity(se)
+                depth++;
+
+        return depth;
+}
+
 /*
  * Preempt the current task with a newly woken task if needed:
  */
@@ -1141,6 +1152,7 @@ static void check_preempt_wakeup(struct rq *rq, struct task_struct *p)
         struct task_struct *curr = rq->curr;
         struct cfs_rq *cfs_rq = task_cfs_rq(curr);
         struct sched_entity *se = &curr->se, *pse = &p->se;
+        int se_depth, pse_depth;
 
         if (unlikely(rt_prio(p->prio))) {
                 update_rq_clock(rq);
@@ -1165,6 +1177,27 @@ static void check_preempt_wakeup(struct rq *rq, struct task_struct *p)
         if (!sched_feat(WAKEUP_PREEMPT))
                 return;
 
+        /*
+         * preemption test can be made between sibling entities who are in the
+         * same cfs_rq i.e who have a common parent. Walk up the hierarchy of
+         * both tasks until we find their ancestors who are siblings of common
+         * parent.
+         */
+
+        /* First walk up until both entities are at same depth */
+        se_depth = depth_se(se);
+        pse_depth = depth_se(pse);
+
+        while (se_depth > pse_depth) {
+                se_depth--;
+                se = parent_entity(se);
+        }
+
+        while (pse_depth > se_depth) {
+                pse_depth--;
+                pse = parent_entity(pse);
+        }
+
         while (!is_same_group(se, pse)) {
                 se = parent_entity(se);
                 pse = parent_entity(pse);
@@ -1223,13 +1256,22 @@ static void put_prev_task_fair(struct rq *rq, struct task_struct *prev)
 static struct task_struct *
 __load_balance_iterator(struct cfs_rq *cfs_rq, struct rb_node *curr)
 {
-        struct task_struct *p;
+        struct task_struct *p = NULL;
+        struct sched_entity *se;
 
         if (!curr)
                 return NULL;
 
-        p = rb_entry(curr, struct task_struct, se.run_node);
-        cfs_rq->rb_load_balance_curr = rb_next(curr);
+        /* Skip over entities that are not tasks */
+        do {
+                se = rb_entry(curr, struct sched_entity, run_node);
+                curr = rb_next(curr);
+        } while (curr && !entity_is_task(se));
+
+        cfs_rq->rb_load_balance_curr = curr;
+
+        if (entity_is_task(se))
+                p = task_of(se);
 
         return p;
 }
@@ -1489,9 +1531,6 @@ static void print_cfs_stats(struct seq_file *m, int cpu)
 {
         struct cfs_rq *cfs_rq;
 
-#ifdef CONFIG_FAIR_GROUP_SCHED
-        print_cfs_rq(m, cpu, &cpu_rq(cpu)->cfs);
-#endif
         rcu_read_lock();
         for_each_leaf_cfs_rq(cpu_rq(cpu), cfs_rq)
                 print_cfs_rq(m, cpu, cfs_rq);