[PATCH 21/30] sched: fix task_h_load()

[Peter Zijlstra]

Currently task_h_load() computes the load of a task and uses that to either
subtract it from the total, or add to it.

However, removing or adding a task need not have any effect on the total load
at all. Imagine adding a task to a group that is local to one cpu - in that
case the total load of that cpu is unaffected.

So properly compute addition/removal:

 s_i = S * rw_i / \Sum_j rw_j
 s'_i = S * (rw_i + wl) / (\Sum_j rw_j + wg)

then s'_i - s_i gives the change in load.

Where s_i is the shares for cpu i, S the group weight, rw_i the runqueue weight
for that cpu, wl the weight we add (subtract) and wg the weight contribution to
the runqueue.

Signed-off-by: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
---
 kernel/sched_fair.c |   49 ++++++++++++++++++++++++++++++++++++++++---------
 1 file changed, 40 insertions(+), 9 deletions(-)

Index: linux-2.6/kernel/sched_fair.c
===================================================================
--- linux-2.6.orig/kernel/sched_fair.c
+++ linux-2.6/kernel/sched_fair.c
@@ -1071,22 +1071,53 @@ static inline int wake_idle(int cpu, str
 static const struct sched_class fair_sched_class;
 
 #ifdef CONFIG_FAIR_GROUP_SCHED
-static unsigned long task_h_load(struct task_struct *p)
+static unsigned long effective_load(struct task_group *tg, long wl, int cpu)
 {
-	unsigned long h_load = p->se.load.weight;
-	struct cfs_rq *cfs_rq = cfs_rq_of(&p->se);
+	struct sched_entity *se = tg->se[cpu];
+	long wg = wl;
 
-	update_h_load(task_cpu(p));
+	for_each_sched_entity(se) {
+#define D(n) (likely(n) ? (n) : 1)
+
+		long S, Srw, rw, s, sn;
+
+		S = se->my_q->tg->shares;
+		s = se->my_q->shares;
+		rw = se->my_q->load.weight;
 
-	h_load = calc_delta_mine(h_load, cfs_rq->h_load, &cfs_rq->load);
+		Srw = S * rw / D(s);
+		sn = S * (rw + wl) / D(Srw + wg);
+
+		wl = sn - s;
+		wg = 0;
+#undef D
+	}
 
-	return h_load;
+	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_h_load(struct task_struct *p)
+
+static unsigned long task_load_sub(struct task_struct *p)
+{
+	return -p->se.load.weight;
+}
+
+static unsigned long task_load_add(struct task_struct *p, int cpu)
 {
 	return p->se.load.weight;
 }
+
 #endif
 
 static int
@@ -1109,9 +1140,9 @@ wake_affine(struct rq *rq, struct sched_
 	 * of the current CPU:
 	 */
 	if (sync)
-		tl -= task_h_load(current);
+		tl += task_load_sub(current);
 
-	balanced = 100*(tl + task_h_load(p)) <= imbalance*load;
+	balanced = 100*(tl + task_load_add(p, this_cpu)) <= imbalance*load;
 
 	/*
 	 * If the currently running task will sleep within

-- 

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