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>

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 3fa3e1839c86a1c50912ac7db2f4943755bb38cb..1f9c4571615d0772d74bbe90b6e5699f89610747 100644 (file)
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -5095,8 +5095,7 @@ static void move_task(struct task_struct *p, struct lb_env *env)
 /*
  * 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 @@ task_hot(struct task_struct *p, u64 now)
        /*
         * 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 @@ task_hot(struct task_struct *p, u64 now)
        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 @@ int can_migrate_task(struct task_struct *p, struct lb_env *env)
         * 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);