sched: optimize update_rq_clock() calls in the load-balancer

optimize update_rq_clock() calls in the load-balancer: update them
right after locking the runqueue(s) so that the pull functions do
not have to call it.

Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 8 insertions, 6 deletions

diff --git a/kernel/sched.c b/kernel/sched.c
index 9ccd91e5b65b..afc59f274e58 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -2017,6 +2017,8 @@ static void double_rq_lock(struct rq *rq1, struct rq *rq2)
                         spin_lock(&rq1->lock);
                 }
         }
+        update_rq_clock(rq1);
+        update_rq_clock(rq2);
 }
 
 /*
@@ -2113,10 +2115,8 @@ void sched_exec(void)
 static void pull_task(struct rq *src_rq, struct task_struct *p,
                       struct rq *this_rq, int this_cpu)
 {
-        update_rq_clock(src_rq);
         deactivate_task(src_rq, p, 0);
         set_task_cpu(p, this_cpu);
-        __update_rq_clock(this_rq);
         activate_task(this_rq, p, 0);
         /*
          * Note that idle threads have a prio of MAX_PRIO, for this test
@@ -2798,6 +2798,8 @@ redo:
         if (busiest->nr_running > 1) {
                 /* Attempt to move tasks */
                 double_lock_balance(this_rq, busiest);
+                /* this_rq->clock is already updated */
+                update_rq_clock(busiest);
                 ld_moved = move_tasks(this_rq, this_cpu, busiest,
                                         imbalance, sd, CPU_NEWLY_IDLE,
                                         &all_pinned);
@@ -2895,6 +2897,8 @@ static void active_load_balance(struct rq *busiest_rq, int busiest_cpu)
 
         /* move a task from busiest_rq to target_rq */
         double_lock_balance(busiest_rq, target_rq);
+        update_rq_clock(busiest_rq);
+        update_rq_clock(target_rq);
 
         /* Search for an sd spanning us and the target CPU. */
         for_each_domain(target_cpu, sd) {
@@ -4962,13 +4966,11 @@ static int __migrate_task(struct task_struct *p, int src_cpu, int dest_cpu)
                 goto out;
 
         on_rq = p->se.on_rq;
-        if (on_rq) {
-                update_rq_clock(rq_src);
+        if (on_rq)
                 deactivate_task(rq_src, p, 0);
-        }
+
         set_task_cpu(p, dest_cpu);
         if (on_rq) {
-                update_rq_clock(rq_dest);
                 activate_task(rq_dest, p, 0);
                 check_preempt_curr(rq_dest, p);
         }