From: Nick Piggin <nickpiggin@yahoo.com.au>
Imbalance calculations were not right. This would cause unneeded migration.
---
25-akpm/kernel/sched.c | 38 ++++++++++++++++++++++----------------
1 files changed, 22 insertions(+), 16 deletions(-)
diff -puN kernel/sched.c~sched-imbalance-fix kernel/sched.c
--- 25/kernel/sched.c~sched-imbalance-fix 2004-03-28 23:16:47.105243480 -0800
+++ 25-akpm/kernel/sched.c 2004-03-28 23:16:47.109242872 -0800
@@ -1395,9 +1395,9 @@ find_busiest_group(struct sched_domain *
for_each_cpu_mask(i, tmp) {
/* Bias balancing toward cpus of our domain */
- if (local_group) {
+ if (local_group)
load = get_high_cpu_load(i);
- } else
+ else
load = get_low_cpu_load(i);
nr_cpus++;
@@ -1417,8 +1417,7 @@ find_busiest_group(struct sched_domain *
this_load = avg_load;
this = group;
goto nextgroup;
- }
- if (avg_load > max_load) {
+ } else if (avg_load > max_load) {
max_load = avg_load;
busiest = group;
}
@@ -1431,11 +1430,9 @@ nextgroup:
avg_load = (SCHED_LOAD_SCALE * total_load) / total_pwr;
- if (idle == NOT_IDLE) {
- if (this_load >= avg_load ||
+ if (this_load >= avg_load ||
100*max_load <= sd->imbalance_pct*this_load)
goto out_balanced;
- }
/*
* We're trying to get all the cpus to the average_load, so we don't
@@ -1448,12 +1445,21 @@ nextgroup:
* by pulling tasks to us. Be careful of negative numbers as they'll
* appear as very large values with unsigned longs.
*/
- *imbalance = (min(max_load - avg_load, avg_load - this_load) + 1) / 2;
+ *imbalance = min(max_load - avg_load, avg_load - this_load);
+
+ /* How much load to actually move to equalise the imbalance */
+ *imbalance = (*imbalance * min(busiest->cpu_power, this->cpu_power))
+ / SCHED_LOAD_SCALE;
- if (*imbalance <= SCHED_LOAD_SCALE/2) {
+ if (*imbalance < SCHED_LOAD_SCALE - 1) {
unsigned long pwr_now = 0, pwr_move = 0;
unsigned long tmp;
+ if (max_load - this_load >= SCHED_LOAD_SCALE*2) {
+ *imbalance = 1;
+ return busiest;
+ }
+
/*
* OK, we don't have enough imbalance to justify moving tasks,
* however we may be able to increase total CPU power used by
@@ -1472,26 +1478,26 @@ nextgroup:
/* Amount of load we'd add */
tmp = SCHED_LOAD_SCALE*SCHED_LOAD_SCALE/this->cpu_power;
- pwr_move += this->cpu_power*min(this->cpu_power, this_load + tmp);
+ if (max_load < tmp)
+ tmp = max_load;
+ pwr_move += this->cpu_power*min(SCHED_LOAD_SCALE, this_load + tmp);
pwr_move /= SCHED_LOAD_SCALE;
/* Move if we gain another 8th of a CPU worth of throughput */
if (pwr_move < pwr_now + SCHED_LOAD_SCALE / 8)
goto out_balanced;
+
*imbalance = 1;
return busiest;
}
- /* How many tasks to actually move to equalise the imbalance */
- *imbalance = (*imbalance * min(busiest->cpu_power, this->cpu_power))
- / SCHED_LOAD_SCALE;
- /* Get rid of the scaling factor, rounding *up* as we divide */
- *imbalance = (*imbalance + SCHED_LOAD_SCALE/2) / SCHED_LOAD_SCALE;
+ /* Get rid of the scaling factor, rounding down as we divide */
+ *imbalance = (*imbalance + 1) / SCHED_LOAD_SCALE;
return busiest;
out_balanced:
- if (busiest && idle == NEWLY_IDLE) {
+ if (busiest && idle != NOT_IDLE && max_load > SCHED_LOAD_SCALE) {
*imbalance = 1;
return busiest;
}
_