When triggering an active load balance, sd->nr_balance_failed is set to
such a value that any further can_migrate_task() using said sd will ignore
the output of task_hot().
This behaviour makes sense, as active load balance intentionally preempts a
rq's running task to migrate it right away, but this asynchronous write is
a bit shoddy, as the stopper thread might run active_load_balance_cpu_stop
before the sd->nr_balance_failed write either becomes visible to the
stopper's CPU or even happens on the CPU that appended the stopper work.
Add a struct lb_env flag to denote active balancing, and use it in
can_migrate_task(). Remove the sd->nr_balance_failed write that served the
same purpose.
Signed-off-by: Valentin Schneider <valentin.schnei...@arm.com>
---
kernel/sched/fair.c | 17 ++++++++++-------
1 file changed, 10 insertions(+), 7 deletions(-)
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 83aea97fbf22..f50a902bdf24 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -7420,6 +7420,7 @@ enum migration_type {
#define LBF_NEED_BREAK 0x02
#define LBF_DST_PINNED 0x04
#define LBF_SOME_PINNED 0x08
+#define LBF_ACTIVE_LB 0x10
struct lb_env {
struct sched_domain *sd;
@@ -7609,10 +7610,14 @@ int can_migrate_task(struct task_struct *p, struct
lb_env *env)
/*
* Aggressive migration if:
- * 1) destination numa is preferred
- * 2) task is cache cold, or
- * 3) too many balance attempts have failed.
+ * 1) active balance
+ * 2) destination numa is preferred
+ * 3) task is cache cold, or
+ * 4) too many balance attempts have failed.
*/
+ if (env->flags & LBF_ACTIVE_LB)
+ return 1;
+
tsk_cache_hot = migrate_degrades_locality(p, env);
if (tsk_cache_hot == -1)
tsk_cache_hot = task_hot(p, env);
@@ -9794,9 +9799,6 @@ static int load_balance(int this_cpu, struct rq *this_rq,
active_load_balance_cpu_stop, busiest,
&busiest->active_balance_work);
}
-
- /* We've kicked active balancing, force task migration.
*/
- sd->nr_balance_failed = sd->cache_nice_tries+1;
}
} else {
sd->nr_balance_failed = 0;
@@ -9952,7 +9954,8 @@ static int active_load_balance_cpu_stop(void *data)
* @dst_grpmask we need to make that test go away with
lying
* about DST_PINNED.
*/
- .flags = LBF_DST_PINNED,
+ .flags = LBF_DST_PINNED |
+ LBF_ACTIVE_LB,
};
schedstat_inc(sd->alb_count);
--
2.25.1
