revert ("sched: fair-group: SMP-nice for group scheduling")

Yanmin Zhang reported:

Comparing with 2.6.25, volanoMark has big regression with kernel 2.6.26-rc1.
It's about 50% on my 8-core stoakley, 16-core tigerton, and Itanium Montecito.

With bisect, I located the following patch:

| 18d95a2832c1392a2d63227a7a6d433cb9f2037e is first bad commit
| commit 18d95a2832c1392a2d63227a7a6d433cb9f2037e
| Author: Peter Zijlstra <a.p.zijlstra@chello.nl>
| Date:   Sat Apr 19 19:45:00 2008 +0200
|
|     sched: fair-group: SMP-nice for group scheduling

Revert it so that we get v2.6.25 behavior.

Bisected-by: Yanmin Zhang <yanmin_zhang@linux.intel.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 44 insertions, 80 deletions

diff --git a/kernel/sched_fair.c b/kernel/sched_fair.c
index 0eb0ae879542..f0f25fc12d0a 100644
--- a/kernel/sched_fair.c
+++ b/kernel/sched_fair.c
@@ -510,27 +510,10 @@ update_stats_curr_start(struct cfs_rq *cfs_rq, struct sched_entity *se)
  * Scheduling class queueing methods:
  */
 
-#if defined CONFIG_SMP && defined CONFIG_FAIR_GROUP_SCHED
-static void
-add_cfs_task_weight(struct cfs_rq *cfs_rq, unsigned long weight)
-{
-        cfs_rq->task_weight += weight;
-}
-#else
-static inline void
-add_cfs_task_weight(struct cfs_rq *cfs_rq, unsigned long weight)
-{
-}
-#endif
-
 static void
 account_entity_enqueue(struct cfs_rq *cfs_rq, struct sched_entity *se)
 {
         update_load_add(&cfs_rq->load, se->load.weight);
-        if (!parent_entity(se))
-                inc_cpu_load(rq_of(cfs_rq), se->load.weight);
-        if (entity_is_task(se))
-                add_cfs_task_weight(cfs_rq, se->load.weight);
         cfs_rq->nr_running++;
         se->on_rq = 1;
         list_add(&se->group_node, &cfs_rq->tasks);
@@ -540,10 +523,6 @@ static void
 account_entity_dequeue(struct cfs_rq *cfs_rq, struct sched_entity *se)
 {
         update_load_sub(&cfs_rq->load, se->load.weight);
-        if (!parent_entity(se))
-                dec_cpu_load(rq_of(cfs_rq), se->load.weight);
-        if (entity_is_task(se))
-                add_cfs_task_weight(cfs_rq, -se->load.weight);
         cfs_rq->nr_running--;
         se->on_rq = 0;
         list_del_init(&se->group_node);
@@ -1327,90 +1306,75 @@ static struct task_struct *load_balance_next_fair(void *arg)
         return __load_balance_iterator(cfs_rq, cfs_rq->balance_iterator);
 }
 
-static unsigned long
-__load_balance_fair(struct rq *this_rq, int this_cpu, struct rq *busiest,
-                unsigned long max_load_move, struct sched_domain *sd,
-                enum cpu_idle_type idle, int *all_pinned, int *this_best_prio,
-                struct cfs_rq *cfs_rq)
+#ifdef CONFIG_FAIR_GROUP_SCHED
+static int cfs_rq_best_prio(struct cfs_rq *cfs_rq)
 {
-        struct rq_iterator cfs_rq_iterator;
+        struct sched_entity *curr;
+        struct task_struct *p;
 
-        cfs_rq_iterator.start = load_balance_start_fair;
-        cfs_rq_iterator.next = load_balance_next_fair;
-        cfs_rq_iterator.arg = cfs_rq;
+        if (!cfs_rq->nr_running || !first_fair(cfs_rq))
+                return MAX_PRIO;
+
+        curr = cfs_rq->curr;
+        if (!curr)
+                curr = __pick_next_entity(cfs_rq);
 
-        return balance_tasks(this_rq, this_cpu, busiest,
-                        max_load_move, sd, idle, all_pinned,
-                        this_best_prio, &cfs_rq_iterator);
+        p = task_of(curr);
+
+        return p->prio;
 }
+#endif
 
-#ifdef CONFIG_FAIR_GROUP_SCHED
 static unsigned long
 load_balance_fair(struct rq *this_rq, int this_cpu, struct rq *busiest,
                   unsigned long max_load_move,
                   struct sched_domain *sd, enum cpu_idle_type idle,
                   int *all_pinned, int *this_best_prio)
 {
+        struct cfs_rq *busy_cfs_rq;
         long rem_load_move = max_load_move;
-        int busiest_cpu = cpu_of(busiest);
-        struct task_group *tg;
-
-        rcu_read_lock();
-        list_for_each_entry(tg, &task_groups, list) {
-                long imbalance;
-                unsigned long this_weight, busiest_weight;
-                long rem_load, max_load, moved_load;
-
-                /*
-                 * empty group
-                 */
-                if (!aggregate(tg, sd)->task_weight)
-                        continue;
-
-                rem_load = rem_load_move * aggregate(tg, sd)->rq_weight;
-                rem_load /= aggregate(tg, sd)->load + 1;
-
-                this_weight = tg->cfs_rq[this_cpu]->task_weight;
-                busiest_weight = tg->cfs_rq[busiest_cpu]->task_weight;
+        struct rq_iterator cfs_rq_iterator;
 
-                imbalance = (busiest_weight - this_weight) / 2;
+        cfs_rq_iterator.start = load_balance_start_fair;
+        cfs_rq_iterator.next = load_balance_next_fair;
 
-                if (imbalance < 0)
-                        imbalance = busiest_weight;
+        for_each_leaf_cfs_rq(busiest, busy_cfs_rq) {
+#ifdef CONFIG_FAIR_GROUP_SCHED
+                struct cfs_rq *this_cfs_rq;
+                long imbalance;
+                unsigned long maxload;
 
-                max_load = max(rem_load, imbalance);
-                moved_load = __load_balance_fair(this_rq, this_cpu, busiest,
-                                max_load, sd, idle, all_pinned, this_best_prio,
-                                tg->cfs_rq[busiest_cpu]);
+                this_cfs_rq = cpu_cfs_rq(busy_cfs_rq, this_cpu);
 
-                if (!moved_load)
+                imbalance = busy_cfs_rq->load.weight - this_cfs_rq->load.weight;
+                /* Don't pull if this_cfs_rq has more load than busy_cfs_rq */
+                if (imbalance <= 0)
                         continue;
 
-                move_group_shares(tg, sd, busiest_cpu, this_cpu);
+                /* Don't pull more than imbalance/2 */
+                imbalance /= 2;
+                maxload = min(rem_load_move, imbalance);
 
-                moved_load *= aggregate(tg, sd)->load;
-                moved_load /= aggregate(tg, sd)->rq_weight + 1;
+                *this_best_prio = cfs_rq_best_prio(this_cfs_rq);
+#else
+# define maxload rem_load_move
+#endif
+                /*
+                 * pass busy_cfs_rq argument into
+                 * load_balance_[start|next]_fair iterators
+                 */
+                cfs_rq_iterator.arg = busy_cfs_rq;
+                rem_load_move -= balance_tasks(this_rq, this_cpu, busiest,
+                                               maxload, sd, idle, all_pinned,
+                                               this_best_prio,
+                                               &cfs_rq_iterator);
 
-                rem_load_move -= moved_load;
-                if (rem_load_move < 0)
+                if (rem_load_move <= 0)
                         break;
         }
-        rcu_read_unlock();
 
         return max_load_move - rem_load_move;
 }
-#else
-static unsigned long
-load_balance_fair(struct rq *this_rq, int this_cpu, struct rq *busiest,
-                  unsigned long max_load_move,
-                  struct sched_domain *sd, enum cpu_idle_type idle,
-                  int *all_pinned, int *this_best_prio)
-{
-        return __load_balance_fair(this_rq, this_cpu, busiest,
-                        max_load_move, sd, idle, all_pinned,
-                        this_best_prio, &busiest->cfs);
-}
-#endif
 
 static int
 move_one_task_fair(struct rq *this_rq, int this_cpu, struct rq *busiest,