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SubjectRe: [PATCH, 2.6.9] improved load_balance() tolerance for pinned tasks
Nick, your patch doesn't work on my 128p to solve the problem.
This variation, however, does work. It's a patch against 2.6.9.
The difference is in move_tasks().






linux-2.6-npiggin/kernel/sched.c | 34 +++++++++++++++++++++++-----------
1 files changed, 23 insertions(+), 11 deletions(-)

Index: linux/kernel/sched.c
===================================================================
--- linux.orig/kernel/sched.c 2004-10-22 09:11:12.000000000 -0700
+++ linux/kernel/sched.c 2004-10-22 11:45:10.000000000 -0700
@@ -1770,7 +1770,7 @@
*/
static inline
int can_migrate_task(task_t *p, runqueue_t *rq, int this_cpu,
- struct sched_domain *sd, enum idle_type idle)
+ struct sched_domain *sd, enum idle_type idle, int *pinned)
{
/*
* We do not migrate tasks that are:
@@ -1780,8 +1780,10 @@
*/
if (task_running(rq, p))
return 0;
- if (!cpu_isset(this_cpu, p->cpus_allowed))
+ if (!cpu_isset(this_cpu, p->cpus_allowed)) {
+ *pinned++;
return 0;
+ }

/* Aggressive migration if we've failed balancing */
if (idle == NEWLY_IDLE ||
@@ -1802,11 +1804,11 @@
*/
static int move_tasks(runqueue_t *this_rq, int this_cpu, runqueue_t *busiest,
unsigned long max_nr_move, struct sched_domain *sd,
- enum idle_type idle)
+ enum idle_type idle, int *all_pinned)
{
prio_array_t *array, *dst_array;
struct list_head *head, *curr;
- int idx, pulled = 0;
+ int idx, examined = 0, pulled = 0, pinned = 0;
task_t *tmp;

if (max_nr_move <= 0 || busiest->nr_running <= 1)
@@ -1850,7 +1852,8 @@

curr = curr->prev;

- if (!can_migrate_task(tmp, busiest, this_cpu, sd, idle)) {
+ examined++;
+ if (!can_migrate_task(tmp, busiest, this_cpu, sd, idle, &pinned)) {
if (curr != head)
goto skip_queue;
idx++;
@@ -1876,6 +1879,8 @@
goto skip_bitmap;
}
out:
+ if (unlikely(examined && examined == pinned))
+ *all_pinned = 1;
return pulled;
}

@@ -2056,7 +2061,7 @@
struct sched_group *group;
runqueue_t *busiest;
unsigned long imbalance;
- int nr_moved;
+ int nr_moved, all_pinned;

spin_lock(&this_rq->lock);
schedstat_inc(sd, lb_cnt[idle]);
@@ -2095,11 +2100,16 @@
*/
double_lock_balance(this_rq, busiest);
nr_moved = move_tasks(this_rq, this_cpu, busiest,
- imbalance, sd, idle);
+ imbalance, sd, idle,
+ &all_pinned);
spin_unlock(&busiest->lock);
}
- spin_unlock(&this_rq->lock);
+ /* All tasks on this runqueue were pinned by CPU affinity */
+ if (unlikely(all_pinned))
+ goto out_balanced;

+ spin_unlock(&this_rq->lock);
+
if (!nr_moved) {
schedstat_inc(sd, lb_failed[idle]);
sd->nr_balance_failed++;
@@ -2154,7 +2164,7 @@
struct sched_group *group;
runqueue_t *busiest = NULL;
unsigned long imbalance;
- int nr_moved = 0;
+ int nr_moved = 0, all_pinned;

schedstat_inc(sd, lb_cnt[NEWLY_IDLE]);
group = find_busiest_group(sd, this_cpu, &imbalance, NEWLY_IDLE);
@@ -2174,7 +2184,7 @@

schedstat_add(sd, lb_imbalance[NEWLY_IDLE], imbalance);
nr_moved = move_tasks(this_rq, this_cpu, busiest,
- imbalance, sd, NEWLY_IDLE);
+ imbalance, sd, NEWLY_IDLE, &all_pinned);
if (!nr_moved)
schedstat_inc(sd, lb_failed[NEWLY_IDLE]);

@@ -2236,6 +2246,7 @@
cpumask_t tmp;
runqueue_t *rq;
int push_cpu = 0;
+ int all_pinned;

if (group == busy_group)
goto next_group;
@@ -2261,7 +2272,8 @@
if (unlikely(busiest == rq))
goto next_group;
double_lock_balance(busiest, rq);
- if (move_tasks(rq, push_cpu, busiest, 1, sd, IDLE)) {
+ if (move_tasks(rq, push_cpu, busiest, 1,
+ sd, IDLE, &all_pinned)) {
schedstat_inc(busiest, alb_lost);
schedstat_inc(rq, alb_gained);
} else {
-
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