Problem:
2 CPU system: if the cpu-0 has two high priority and cpu-1 has one
normal priority task, how can the current code detect this imbalance
because imbalance will be always < busiest_load_per_task and max_load -
this_load will be < 2 * busiest_load_per_task and pwr_move will be <=
pwr_now.
Solution:
Modify the assessment of small imbalances to take into account the
relative sizes of busiest_load_per_task and this_load_per_task. This is
exploiting the fact that if the difference between the loads is greater
than busiest_load_per_task and busiest_load_per_task is greater than
this_load_per_task then moving busiest_load_per_task worth of load from
busiest to this will be an improvement in the distribution of weighted load.
Required patches:
sched-prevent-high-load-weight-tasks-suppressing-balancing.patch
sched-improve-stability-of-smpnice-load-balancing.patch
Note: This patch makes no change to load balancing in the case where all
tasks are nice==0.
Signed-off-by: Peter Williams <[email protected]>
--
Peter Williams [email protected]
"Learning, n. The kind of ignorance distinguishing the studious."
-- Ambrose Bierce
Index: MM-2.6.X/kernel/sched.c
===================================================================
--- MM-2.6.X.orig/kernel/sched.c 2006-04-04 15:18:19.000000000 +1000
+++ MM-2.6.X/kernel/sched.c 2006-04-04 15:53:48.000000000 +1000
@@ -2252,8 +2252,16 @@ find_busiest_group(struct sched_domain *
if (*imbalance < busiest_load_per_task) {
unsigned long pwr_now = 0, pwr_move = 0;
unsigned long tmp;
+ unsigned int imbn = 2;
- if (max_load - this_load >= busiest_load_per_task*2) {
+ if (this_nr_running) {
+ this_load_per_task /= this_nr_running;
+ if (busiest_load_per_task > this_load_per_task)
+ imbn = 1;
+ } else
+ this_load_per_task = SCHED_LOAD_SCALE;
+
+ if (max_load - this_load >= busiest_load_per_task * imbn) {
*imbalance = busiest_load_per_task;
return busiest;
}
@@ -2266,10 +2274,6 @@ find_busiest_group(struct sched_domain *
pwr_now += busiest->cpu_power *
min(busiest_load_per_task, max_load);
- if (this_nr_running)
- this_load_per_task /= this_nr_running;
- else
- this_load_per_task = SCHED_LOAD_SCALE;
pwr_now += this->cpu_power *
min(this_load_per_task, this_load);
pwr_now /= SCHED_LOAD_SCALE;
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