To force a task migration during active balancing, nr_balance_failed is set
to cache_nice_tries + 1. However nr_balance_failed is not reset. As a side
effect, the next regular load balance under the same sd, a cache hot task
might be migrated, just because nr_balance_failed count is high.
Resetting the nr_balance_failed after a successful active balance, ensures
that a hot task is not unreasonably migrated. This can be verified by
looking at number of hot task migrations reported by /proc/schedstat.
Signed-off-by: Srikar Dronamraju <sri...@linux.vnet.ibm.com>
---
kernel/sched/fair.c | 12 ++++++------
1 file changed, 6 insertions(+), 6 deletions(-)
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 9abfb16..fae05f4 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -7294,10 +7294,7 @@ static int load_balance(int this_cpu, struct rq *this_rq,
&busiest->active_balance_work);
}
- /*
- * We've kicked active balancing, reset the failure
- * counter.
- */
+ /* We've kicked active balancing, force task migration.
*/
sd->nr_balance_failed = sd->cache_nice_tries+1;
}
} else
@@ -7532,10 +7529,13 @@ static int active_load_balance_cpu_stop(void *data)
schedstat_inc(sd, alb_count);
p = detach_one_task(&env);
- if (p)
+ if (p) {
schedstat_inc(sd, alb_pushed);
- else
+ /* Active balancing done, reset the failure counter. */
+ sd->nr_balance_failed = 0;
+ } else {
schedstat_inc(sd, alb_failed);
+ }
}
rcu_read_unlock();
out_unlock:
--
1.8.3.1
