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Commit 83378269 authored by Peter Zijlstra's avatar Peter Zijlstra Committed by Ingo Molnar
Browse files

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: default avatarPeter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Srivatsa Vaddagiri <vatsa@linux.vnet.ibm.com>
Cc: Mike Galbraith <efault@gmx.de>
Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
parent 243e0e7b

kernel/sched.c

+4 −0
Original line number Diff line number Diff line
@@ -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 */

kernel/sched_fair.c

+26 −22
Original line number Diff line number Diff line
@@ -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