sched: correct wakeup weight calculations

rw_i = {2, 4, 1, 0}
s_i = {2/7, 4/7, 1/7, 0}

wakeup on cpu0, weight=1

rw'_i = {3, 4, 1, 0}
s'_i = {3/8, 4/8, 1/8, 0}

s_0 = S * rw_0 / \Sum rw_j ->
  \Sum rw_j = S*rw_0/s_0 = 1*2*7/2 = 7 (correct)

s'_0 = S * (rw_0 + 1) / (\Sum rw_j + 1) =
       1 * (2+1) / (7+1) = 3/8 (correct

so we find that adding 1 to cpu0 gains 5/56 in weight
if say the other cpu were, cpu1, we'd also have to calculate its 4/56 loss

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Srivatsa Vaddagiri <vatsa@linux.vnet.ibm.com>
Cc: Mike Galbraith <efault@gmx.de>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

diff --git a/kernel/sched.c b/kernel/sched.c
index 62db0891025aee964709c6dafeeec0e7be166492..01d3e51b7116142d4b3165213eeeacb30378c864 100644 (file)
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -365,6 +365,10 @@ static inline void set_task_rq(struct task_struct *p, unsigned int cpu)
 #else
 
 static inline void set_task_rq(struct task_struct *p, unsigned int cpu) { }
+static inline struct task_group *task_group(struct task_struct *p)
+{
+       return NULL;
+}
 
 #endif /* CONFIG_GROUP_SCHED */
 

diff --git a/kernel/sched_fair.c b/kernel/sched_fair.c
index 26ebe180cdeaf072da9021e04e1810fcce40f016..bed2f71e63d9168318b1143326638ae43dad3aba 100644 (file)
--- a/kernel/sched_fair.c
+++ b/kernel/sched_fair.c
@@ -1074,10 +1074,10 @@ static inline int wake_idle(int cpu, struct task_struct *p)
 static const struct sched_class fair_sched_class;
 
 #ifdef CONFIG_FAIR_GROUP_SCHED
-static unsigned long effective_load(struct task_group *tg, long wl, int cpu)
+static unsigned long effective_load(struct task_group *tg, int cpu,
+               unsigned long wl, unsigned long wg)
 {
        struct sched_entity *se = tg->se[cpu];
-       long wg = wl;
 
        for_each_sched_entity(se) {
 #define D(n) (likely(n) ? (n) : 1)
@@ -1092,6 +1092,13 @@ static unsigned long effective_load(struct task_group *tg, long wl, int cpu)
                b = S*rw + s*wg;
 
                wl = s*(a-b)/D(b);
+               /*
+                * Assume the group is already running and will
+                * thus already be accounted for in the weight.
+                *
+                * That is, moving shares between CPUs, does not
+                * alter the group weight.
+                */
                wg = 0;
 #undef D
        }
@@ -1099,26 +1106,12 @@ static unsigned long effective_load(struct task_group *tg, long wl, int cpu)
        return wl;
 }
 
-static unsigned long task_load_sub(struct task_struct *p)
-{
-       return effective_load(task_group(p), -(long)p->se.load.weight, task_cpu(p));
-}
-
-static unsigned long task_load_add(struct task_struct *p, int cpu)
-{
-       return effective_load(task_group(p), p->se.load.weight, cpu);
-}
-
 #else
 
-static unsigned long task_load_sub(struct task_struct *p)
+static inline unsigned long effective_load(struct task_group *tg, int cpu,
+               unsigned long wl, unsigned long wg)
 {
-       return -p->se.load.weight;
-}
-
-static unsigned long task_load_add(struct task_struct *p, int cpu)
-{
-       return p->se.load.weight;
+       return wl;
 }
 
 #endif
@@ -1130,8 +1123,10 @@ wake_affine(struct rq *rq, struct sched_domain *this_sd, struct rq *this_rq,
            unsigned int imbalance)
 {
        struct task_struct *curr = this_rq->curr;
+       struct task_group *tg;
        unsigned long tl = this_load;
        unsigned long tl_per_task;
+       unsigned long weight;
        int balanced;
 
        if (!(this_sd->flags & SD_WAKE_AFFINE) || !sched_feat(AFFINE_WAKEUPS))
@@ -1142,10 +1137,19 @@ wake_affine(struct rq *rq, struct sched_domain *this_sd, struct rq *this_rq,
         * effect of the currently running task from the load
         * of the current CPU:
         */
-       if (sync)
-               tl += task_load_sub(current);
+       if (sync) {
+               tg = task_group(current);
+               weight = current->se.load.weight;
+
+               tl += effective_load(tg, this_cpu, -weight, -weight);
+               load += effective_load(tg, prev_cpu, 0, -weight);
+       }
+
+       tg = task_group(p);
+       weight = p->se.load.weight;
 
-       balanced = 100*(tl + task_load_add(p, this_cpu)) <= imbalance*load;
+       balanced = 100*(tl + effective_load(tg, this_cpu, weight, weight)) <=
+               imbalance*(load + effective_load(tg, prev_cpu, 0, weight));
 
        /*
         * If the currently running task will sleep within