commit 5d5e2b1bcbdc996e72815c03fdc5ea82c4642397
author Hillf Danton <dhillf@gmail.com> Tue Jun 10 10:58:43 2014 +0200
committer Ingo Molnar <mingo@kernel.org> Wed Jun 18 18:29:59 2014 +0200
tree ca7417f06a98918e05142c9e52481e5eaea8d894
parent bb97fc31647539f1f102eed646a95e200160a150

sched: Fix CACHE_HOT_BUDY condition

When computing cache hot, we should check if the migration dst cpu is idle,
instead of the current cpu. Though they are same in normal balancing, that
is false nowadays in nohz idle balancing at least.

Signed-off-by: Hillf Danton <dhillf@gmail.com>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Cc: Hillf Danton <hillf.zj@alibaba-inc.com>
Cc: Mike Galbraith <mgalbraith@suse.de>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: http://lkml.kernel.org/r/20140607090452.4696E301D2@webmail.sinamail.sina.com.cn
Signed-off-by: Ingo Molnar <mingo@kernel.org>

kernel/sched/fair.c

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 3fa3e18..1f9c457 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -5095,8 +5095,7 @@
 /*
  * Is this task likely cache-hot:
  */
-static int
-task_hot(struct task_struct *p, u64 now)
+static int task_hot(struct task_struct *p, struct lb_env *env)
 {
 	s64 delta;
 
@@ -5109,7 +5108,7 @@
 	/*
 	 * Buddy candidates are cache hot:
 	 */
-	if (sched_feat(CACHE_HOT_BUDDY) && this_rq()->nr_running &&
+	if (sched_feat(CACHE_HOT_BUDDY) && env->dst_rq->nr_running &&
 			(&p->se == cfs_rq_of(&p->se)->next ||
 			 &p->se == cfs_rq_of(&p->se)->last))
 		return 1;
@@ -5119,7 +5118,7 @@
 	if (sysctl_sched_migration_cost == 0)
 		return 0;
 
-	delta = now - p->se.exec_start;
+	delta = rq_clock_task(env->src_rq) - p->se.exec_start;
 
 	return delta < (s64)sysctl_sched_migration_cost;
 }
@@ -5273,7 +5272,7 @@
 	 * 2) task is cache cold, or
 	 * 3) too many balance attempts have failed.
 	 */
-	tsk_cache_hot = task_hot(p, rq_clock_task(env->src_rq));
+	tsk_cache_hot = task_hot(p, env);
 	if (!tsk_cache_hot)
 		tsk_cache_hot = migrate_degrades_locality(p, env);