[PATCH 28/30] sched: correct wakeup weight calculations

Peter Zijlstra
2008-06-27T12:03:55Z

[-- Attachment #1: sched-effective_load.patch --]
[-- Type: text/plain, Size: 3792 bytes --]

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>
---
kernel/sched_fair.c | 48 ++++++++++++++++++++++++++----------------------
1 file changed, 26 insertions(+), 22 deletions(-)

Index: linux-2.6/kernel/sched_fair.c
===================================================================
--- linux-2.6.orig/kernel/sched_fair.c
+++ linux-2.6/kernel/sched_fair.c
@@ -1074,10 +1074,10 @@ static inline int wake_idle(int cpu, str
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(stru
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(stru
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_
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_
* 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
Index: linux-2.6/kernel/sched.c
===================================================================
--- linux-2.6.orig/kernel/sched.c
+++ linux-2.6/kernel/sched.c
@@ -363,6 +363,10 @@ static inline void set_task_rq(struct ta
#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 */

--