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, 31 insertions, 399 deletions

diff --git a/kernel/sched.c b/kernel/sched.c
index 3dc13f05b10e..bfb8ad8ed171 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -398,43 +398,6 @@ struct cfs_rq {
          */
         struct list_head leaf_cfs_rq_list;
         struct task_group *tg;  /* group that "owns" this runqueue */
-
-#ifdef CONFIG_SMP
-        unsigned long task_weight;
-        unsigned long shares;
-        /*
-         * We need space to build a sched_domain wide view of the full task
-         * group tree, in order to avoid depending on dynamic memory allocation
-         * during the load balancing we place this in the per cpu task group
-         * hierarchy. This limits the load balancing to one instance per cpu,
-         * but more should not be needed anyway.
-         */
-        struct aggregate_struct {
-                /*
-                 *   load = weight(cpus) * f(tg)
-                 *
-                 * Where f(tg) is the recursive weight fraction assigned to
-                 * this group.
-                 */
-                unsigned long load;
-
-                /*
-                 * part of the group weight distributed to this span.
-                 */
-                unsigned long shares;
-
-                /*
-                 * The sum of all runqueue weights within this span.
-                 */
-                unsigned long rq_weight;
-
-                /*
-                 * Weight contributed by tasks; this is the part we can
-                 * influence by moving tasks around.
-                 */
-                unsigned long task_weight;
-        } aggregate;
-#endif
 #endif
 };
 
@@ -1508,326 +1471,6 @@ static unsigned long source_load(int cpu, int type);
 static unsigned long target_load(int cpu, int type);
 static unsigned long cpu_avg_load_per_task(int cpu);
 static int task_hot(struct task_struct *p, u64 now, struct sched_domain *sd);
-
-#ifdef CONFIG_FAIR_GROUP_SCHED
-
-/*
- * Group load balancing.
- *
- * We calculate a few balance domain wide aggregate numbers; load and weight.
- * Given the pictures below, and assuming each item has equal weight:
- *
- *         root          1 - thread
- *         / | \         A - group
- *        A  1  B
- *       /|\   / \
- *      C 2 D 3   4
- *      |   |
- *      5   6
- *
- * load:
- *    A and B get 1/3-rd of the total load. C and D get 1/3-rd of A's 1/3-rd,
- *    which equals 1/9-th of the total load.
- *
- * shares:
- *    The weight of this group on the selected cpus.
- *
- * rq_weight:
- *    Direct sum of all the cpu's their rq weight, e.g. A would get 3 while
- *    B would get 2.
- *
- * task_weight:
- *    Part of the rq_weight contributed by tasks; all groups except B would
- *    get 1, B gets 2.
- */
-
-static inline struct aggregate_struct *
-aggregate(struct task_group *tg, struct sched_domain *sd)
-{
-        return &tg->cfs_rq[sd->first_cpu]->aggregate;
-}
-
-typedef void (*aggregate_func)(struct task_group *, struct sched_domain *);
-
-/*
- * Iterate the full tree, calling @down when first entering a node and @up when
- * leaving it for the final time.
- */
-static
-void aggregate_walk_tree(aggregate_func down, aggregate_func up,
-                         struct sched_domain *sd)
-{
-        struct task_group *parent, *child;
-
-        rcu_read_lock();
-        parent = &root_task_group;
-down:
-        (*down)(parent, sd);
-        list_for_each_entry_rcu(child, &parent->children, siblings) {
-                parent = child;
-                goto down;
-
-up:
-                continue;
-        }
-        (*up)(parent, sd);
-
-        child = parent;
-        parent = parent->parent;
-        if (parent)
-                goto up;
-        rcu_read_unlock();
-}
-
-/*
- * Calculate the aggregate runqueue weight.
- */
-static
-void aggregate_group_weight(struct task_group *tg, struct sched_domain *sd)
-{
-        unsigned long rq_weight = 0;
-        unsigned long task_weight = 0;
-        int i;
-
-        for_each_cpu_mask(i, sd->span) {
-                rq_weight += tg->cfs_rq[i]->load.weight;
-                task_weight += tg->cfs_rq[i]->task_weight;
-        }
-
-        aggregate(tg, sd)->rq_weight = rq_weight;
-        aggregate(tg, sd)->task_weight = task_weight;
-}
-
-/*
- * Compute the weight of this group on the given cpus.
- */
-static
-void aggregate_group_shares(struct task_group *tg, struct sched_domain *sd)
-{
-        unsigned long shares = 0;
-        int i;
-
-        for_each_cpu_mask(i, sd->span)
-                shares += tg->cfs_rq[i]->shares;
-
-        if ((!shares && aggregate(tg, sd)->rq_weight) || shares > tg->shares)
-                shares = tg->shares;
-
-        aggregate(tg, sd)->shares = shares;
-}
-
-/*
- * Compute the load fraction assigned to this group, relies on the aggregate
- * weight and this group's parent's load, i.e. top-down.
- */
-static
-void aggregate_group_load(struct task_group *tg, struct sched_domain *sd)
-{
-        unsigned long load;
-
-        if (!tg->parent) {
-                int i;
-
-                load = 0;
-                for_each_cpu_mask(i, sd->span)
-                        load += cpu_rq(i)->load.weight;
-
-        } else {
-                load = aggregate(tg->parent, sd)->load;
-
-                /*
-                 * shares is our weight in the parent's rq so
-                 * shares/parent->rq_weight gives our fraction of the load
-                 */
-                load *= aggregate(tg, sd)->shares;
-                load /= aggregate(tg->parent, sd)->rq_weight + 1;
-        }
-
-        aggregate(tg, sd)->load = load;
-}
-
-static void __set_se_shares(struct sched_entity *se, unsigned long shares);
-
-/*
- * Calculate and set the cpu's group shares.
- */
-static void
-__update_group_shares_cpu(struct task_group *tg, struct sched_domain *sd,
-                          int tcpu)
-{
-        int boost = 0;
-        unsigned long shares;
-        unsigned long rq_weight;
-
-        if (!tg->se[tcpu])
-                return;
-
-        rq_weight = tg->cfs_rq[tcpu]->load.weight;
-
-        /*
-         * If there are currently no tasks on the cpu pretend there is one of
-         * average load so that when a new task gets to run here it will not
-         * get delayed by group starvation.
-         */
-        if (!rq_weight) {
-                boost = 1;
-                rq_weight = NICE_0_LOAD;
-        }
-
-        /*
-         *           \Sum shares * rq_weight
-         * shares =  -----------------------
-         *               \Sum rq_weight
-         *
-         */
-        shares = aggregate(tg, sd)->shares * rq_weight;
-        shares /= aggregate(tg, sd)->rq_weight + 1;
-
-        /*
-         * record the actual number of shares, not the boosted amount.
-         */
-        tg->cfs_rq[tcpu]->shares = boost ? 0 : shares;
-
-        if (shares < MIN_SHARES)
-                shares = MIN_SHARES;
-        else if (shares > MAX_SHARES)
-                shares = MAX_SHARES;
-
-        __set_se_shares(tg->se[tcpu], shares);
-}
-
-/*
- * Re-adjust the weights on the cpu the task came from and on the cpu the
- * task went to.
- */
-static void
-__move_group_shares(struct task_group *tg, struct sched_domain *sd,
-                    int scpu, int dcpu)
-{
-        unsigned long shares;
-
-        shares = tg->cfs_rq[scpu]->shares + tg->cfs_rq[dcpu]->shares;
-
-        __update_group_shares_cpu(tg, sd, scpu);
-        __update_group_shares_cpu(tg, sd, dcpu);
-
-        /*
-         * ensure we never loose shares due to rounding errors in the
-         * above redistribution.
-         */
-        shares -= tg->cfs_rq[scpu]->shares + tg->cfs_rq[dcpu]->shares;
-        if (shares)
-                tg->cfs_rq[dcpu]->shares += shares;
-}
-
-/*
- * Because changing a group's shares changes the weight of the super-group
- * we need to walk up the tree and change all shares until we hit the root.
- */
-static void
-move_group_shares(struct task_group *tg, struct sched_domain *sd,
-                  int scpu, int dcpu)
-{
-        while (tg) {
-                __move_group_shares(tg, sd, scpu, dcpu);
-                tg = tg->parent;
-        }
-}
-
-static
-void aggregate_group_set_shares(struct task_group *tg, struct sched_domain *sd)
-{
-        unsigned long shares = aggregate(tg, sd)->shares;
-        int i;
-
-        for_each_cpu_mask(i, sd->span) {
-                struct rq *rq = cpu_rq(i);
-                unsigned long flags;
-
-                spin_lock_irqsave(&rq->lock, flags);
-                __update_group_shares_cpu(tg, sd, i);
-                spin_unlock_irqrestore(&rq->lock, flags);
-        }
-
-        aggregate_group_shares(tg, sd);
-
-        /*
-         * ensure we never loose shares due to rounding errors in the
-         * above redistribution.
-         */
-        shares -= aggregate(tg, sd)->shares;
-        if (shares) {
-                tg->cfs_rq[sd->first_cpu]->shares += shares;
-                aggregate(tg, sd)->shares += shares;
-        }
-}
-
-/*
- * Calculate the accumulative weight and recursive load of each task group
- * while walking down the tree.
- */
-static
-void aggregate_get_down(struct task_group *tg, struct sched_domain *sd)
-{
-        aggregate_group_weight(tg, sd);
-        aggregate_group_shares(tg, sd);
-        aggregate_group_load(tg, sd);
-}
-
-/*
- * Rebalance the cpu shares while walking back up the tree.
- */
-static
-void aggregate_get_up(struct task_group *tg, struct sched_domain *sd)
-{
-        aggregate_group_set_shares(tg, sd);
-}
-
-static DEFINE_PER_CPU(spinlock_t, aggregate_lock);
-
-static void __init init_aggregate(void)
-{
-        int i;
-
-        for_each_possible_cpu(i)
-                spin_lock_init(&per_cpu(aggregate_lock, i));
-}
-
-static int get_aggregate(struct sched_domain *sd)
-{
-        if (!spin_trylock(&per_cpu(aggregate_lock, sd->first_cpu)))
-                return 0;
-
-        aggregate_walk_tree(aggregate_get_down, aggregate_get_up, sd);
-        return 1;
-}
-
-static void put_aggregate(struct sched_domain *sd)
-{
-        spin_unlock(&per_cpu(aggregate_lock, sd->first_cpu));
-}
-
-static void cfs_rq_set_shares(struct cfs_rq *cfs_rq, unsigned long shares)
-{
-        cfs_rq->shares = shares;
-}
-
-#else
-
-static inline void init_aggregate(void)
-{
-}
-
-static inline int get_aggregate(struct sched_domain *sd)
-{
-        return 0;
-}
-
-static inline void put_aggregate(struct sched_domain *sd)
-{
-}
-#endif
-
 #else /* CONFIG_SMP */
 
 #ifdef CONFIG_FAIR_GROUP_SCHED
@@ -1848,14 +1491,26 @@ static void cfs_rq_set_shares(struct cfs_rq *cfs_rq, unsigned long shares)
 
 #define sched_class_highest (&rt_sched_class)
 
-static void inc_nr_running(struct rq *rq)
+static inline void inc_load(struct rq *rq, const struct task_struct *p)
+{
+        update_load_add(&rq->load, p->se.load.weight);
+}
+
+static inline void dec_load(struct rq *rq, const struct task_struct *p)
+{
+        update_load_sub(&rq->load, p->se.load.weight);
+}
+
+static void inc_nr_running(struct task_struct *p, struct rq *rq)
 {
         rq->nr_running++;
+        inc_load(rq, p);
 }
 
-static void dec_nr_running(struct rq *rq)
+static void dec_nr_running(struct task_struct *p, struct rq *rq)
 {
         rq->nr_running--;
+        dec_load(rq, p);
 }
 
 static void set_load_weight(struct task_struct *p)
@@ -1947,7 +1602,7 @@ static void activate_task(struct rq *rq, struct task_struct *p, int wakeup)
                 rq->nr_uninterruptible--;
 
         enqueue_task(rq, p, wakeup);
-        inc_nr_running(rq);
+        inc_nr_running(p, rq);
 }
 
 /*
@@ -1959,7 +1614,7 @@ static void deactivate_task(struct rq *rq, struct task_struct *p, int sleep)
                 rq->nr_uninterruptible++;
 
         dequeue_task(rq, p, sleep);
-        dec_nr_running(rq);
+        dec_nr_running(p, rq);
 }
 
 /**
@@ -2612,7 +2267,7 @@ void wake_up_new_task(struct task_struct *p, unsigned long clone_flags)
                  * management (if any):
                  */
                 p->sched_class->task_new(rq, p);
-                inc_nr_running(rq);
+                inc_nr_running(p, rq);
         }
         check_preempt_curr(rq, p);
 #ifdef CONFIG_SMP
@@ -3603,12 +3258,9 @@ static int load_balance(int this_cpu, struct rq *this_rq,
         unsigned long imbalance;
         struct rq *busiest;
         unsigned long flags;
-        int unlock_aggregate;
 
         cpus_setall(*cpus);
 
-        unlock_aggregate = get_aggregate(sd);
-
         /*
          * When power savings policy is enabled for the parent domain, idle
          * sibling can pick up load irrespective of busy siblings. In this case,
@@ -3724,9 +3376,8 @@ redo:
 
         if (!ld_moved && !sd_idle && sd->flags & SD_SHARE_CPUPOWER &&
             !test_sd_parent(sd, SD_POWERSAVINGS_BALANCE))
-                ld_moved = -1;
-
-        goto out;
+                return -1;
+        return ld_moved;
 
 out_balanced:
         schedstat_inc(sd, lb_balanced[idle]);
@@ -3741,13 +3392,8 @@ out_one_pinned:
 
         if (!sd_idle && sd->flags & SD_SHARE_CPUPOWER &&
             !test_sd_parent(sd, SD_POWERSAVINGS_BALANCE))
-                ld_moved = -1;
-        else
-                ld_moved = 0;
-out:
-        if (unlock_aggregate)
-                put_aggregate(sd);
-        return ld_moved;
+                return -1;
+        return 0;
 }
 
 /*
@@ -4934,8 +4580,10 @@ void set_user_nice(struct task_struct *p, long nice)
                 goto out_unlock;
         }
         on_rq = p->se.on_rq;
-        if (on_rq)
+        if (on_rq) {
                 dequeue_task(rq, p, 0);
+                dec_load(rq, p);
+        }
 
         p->static_prio = NICE_TO_PRIO(nice);
         set_load_weight(p);
@@ -4945,6 +4593,7 @@ void set_user_nice(struct task_struct *p, long nice)
 
         if (on_rq) {
                 enqueue_task(rq, p, 0);
+                inc_load(rq, p);
                 /*
                  * If the task increased its priority or is running and
                  * lowered its priority, then reschedule its CPU:
@@ -7319,7 +6968,6 @@ static int __build_sched_domains(const cpumask_t *cpu_map,
                         SD_INIT(sd, ALLNODES);
                         set_domain_attribute(sd, attr);
                         sd->span = *cpu_map;
-                        sd->first_cpu = first_cpu(sd->span);
                         cpu_to_allnodes_group(i, cpu_map, &sd->groups, tmpmask);
                         p = sd;
                         sd_allnodes = 1;
@@ -7330,7 +6978,6 @@ static int __build_sched_domains(const cpumask_t *cpu_map,
                 SD_INIT(sd, NODE);
                 set_domain_attribute(sd, attr);
                 sched_domain_node_span(cpu_to_node(i), &sd->span);
-                sd->first_cpu = first_cpu(sd->span);
                 sd->parent = p;
                 if (p)
                         p->child = sd;
@@ -7342,7 +6989,6 @@ static int __build_sched_domains(const cpumask_t *cpu_map,
                 SD_INIT(sd, CPU);
                 set_domain_attribute(sd, attr);
                 sd->span = *nodemask;
-                sd->first_cpu = first_cpu(sd->span);
                 sd->parent = p;
                 if (p)
                         p->child = sd;
@@ -7354,7 +7000,6 @@ static int __build_sched_domains(const cpumask_t *cpu_map,
                 SD_INIT(sd, MC);
                 set_domain_attribute(sd, attr);
                 sd->span = cpu_coregroup_map(i);
-                sd->first_cpu = first_cpu(sd->span);
                 cpus_and(sd->span, sd->span, *cpu_map);
                 sd->parent = p;
                 p->child = sd;
@@ -7367,7 +7012,6 @@ static int __build_sched_domains(const cpumask_t *cpu_map,
                 SD_INIT(sd, SIBLING);
                 set_domain_attribute(sd, attr);
                 sd->span = per_cpu(cpu_sibling_map, i);
-                sd->first_cpu = first_cpu(sd->span);
                 cpus_and(sd->span, sd->span, *cpu_map);
                 sd->parent = p;
                 p->child = sd;
@@ -8037,7 +7681,6 @@ void __init sched_init(void)
         }
 
 #ifdef CONFIG_SMP
-        init_aggregate();
         init_defrootdomain();
 #endif
 
@@ -8602,11 +8245,14 @@ void sched_move_task(struct task_struct *tsk)
 #endif
 
 #ifdef CONFIG_FAIR_GROUP_SCHED
-static void __set_se_shares(struct sched_entity *se, unsigned long shares)
+static void set_se_shares(struct sched_entity *se, unsigned long shares)
 {
         struct cfs_rq *cfs_rq = se->cfs_rq;
+        struct rq *rq = cfs_rq->rq;
         int on_rq;
 
+        spin_lock_irq(&rq->lock);
+
         on_rq = se->on_rq;
         if (on_rq)
                 dequeue_entity(cfs_rq, se, 0);
@@ -8616,17 +8262,8 @@ static void __set_se_shares(struct sched_entity *se, unsigned long shares)
 
         if (on_rq)
                 enqueue_entity(cfs_rq, se, 0);
-}
 
-static void set_se_shares(struct sched_entity *se, unsigned long shares)
-{
-        struct cfs_rq *cfs_rq = se->cfs_rq;
-        struct rq *rq = cfs_rq->rq;
-        unsigned long flags;
-
-        spin_lock_irqsave(&rq->lock, flags);
-        __set_se_shares(se, shares);
-        spin_unlock_irqrestore(&rq->lock, flags);
+        spin_unlock_irq(&rq->lock);
 }
 
 static DEFINE_MUTEX(shares_mutex);
@@ -8665,13 +8302,8 @@ int sched_group_set_shares(struct task_group *tg, unsigned long shares)
          * w/o tripping rebalance_share or load_balance_fair.
          */
         tg->shares = shares;
-        for_each_possible_cpu(i) {
-                /*
-                 * force a rebalance
-                 */
-                cfs_rq_set_shares(tg->cfs_rq[i], 0);
+        for_each_possible_cpu(i)
                 set_se_shares(tg->se[i], shares);
-        }
 
         /*
          * Enable load balance activity on this group, by inserting it back on