Commit fa3b6ddc authored by Siddha, Suresh B's avatar Siddha, Suresh B Committed by Linus Torvalds
Browse files

[PATCH] sched: don't kick ALB in the presence of pinned task

Jack Steiner brought this issue at my OLS talk.

Take a scenario where two tasks are pinned to two HT threads in a physical
package.  Idle packages in the system will keep kicking migration_thread on
the busy package with out any success.

We will run into similar scenarios in the presence of CMP/NUMA.
Signed-off-by: default avatarSuresh Siddha <>
Acked-by: default avatarIngo Molnar <>
Signed-off-by: default avatarAndrew Morton <>
Signed-off-by: default avatarLinus Torvalds <>
parent 5927ad78
......@@ -2125,6 +2125,16 @@ static int load_balance(int this_cpu, runqueue_t *this_rq,
if (unlikely(sd->nr_balance_failed > sd->cache_nice_tries+2)) {
/* don't kick the migration_thread, if the curr
* task on busiest cpu can't be moved to this_cpu
if (!cpu_isset(this_cpu, busiest->curr->cpus_allowed)) {
all_pinned = 1;
goto out_one_pinned;
if (!busiest->active_balance) {
busiest->active_balance = 1;
busiest->push_cpu = this_cpu;
......@@ -2165,6 +2175,8 @@ out_balanced:
schedstat_inc(sd, lb_balanced[idle]);
sd->nr_balance_failed = 0;
/* tune up the balancing interval */
if ((all_pinned && sd->balance_interval < MAX_PINNED_INTERVAL) ||
(sd->balance_interval < sd->max_interval))
......@@ -2357,7 +2369,8 @@ static void rebalance_tick(int this_cpu, runqueue_t *this_rq,
if (j - sd->last_balance >= interval) {
if (load_balance(this_cpu, this_rq, sd, idle)) {
/* We've pulled tasks over so either we're no
* We've pulled tasks over so either we're no
* longer idle, or one of our SMT siblings is
* not idle.
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