UPSTREAM: sched/fair: Compute task/cpu utilization at wake-up correctly

At task wake-up load-tracking isn't updated until the task is enqueued.
The task's own view of its utilization contribution may therefore not be
aligned with its contribution to the cfs_rq load-tracking which may have
been updated in the meantime. Basically, the task's own utilization
hasn't yet accounted for the sleep decay, while the cfs_rq may have
(partially). Estimating the cfs_rq utilization in case the task is
migrated at wake-up as task_rq(p)->cfs.avg.util_avg - p->se.avg.util_avg
is therefore incorrect as the two load-tracking signals aren't time
synchronized (different last update).

To solve this problem, this patch synchronizes the task utilization with
its previous rq before the task utilization is used in the wake-up path.
Currently the update/synchronization is done _after_ the task has been
placed by select_task_rq_fair(). The synchronization is done without
having to take the rq lock using the existing mechanism used in
remove_entity_load_avg().

Change-Id: I5605cca0c94c6ba43d9ce11554765a2456cf85bc
Signed-off-by: Morten Rasmussen <morten.rasmussen@arm.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: dietmar.eggemann@arm.com
Cc: freedom.tan@mediatek.com
Cc: keita.kobayashi.ym@renesas.com
Cc: mgalbraith@suse.de
Cc: sgurrappadi@nvidia.com
Cc: vincent.guittot@linaro.org
Cc: yuyang.du@intel.com
Link: http://lkml.kernel.org/r/1476452472-24740-2-git-send-email-morten.rasmussen@arm.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
(cherry picked from commit 104cb16d9eb684f071d5bf3aa87c0d01af259b7c)
Signed-off-by: Chris Redpath <chris.redpath@arm.com>

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 19edbc48b1bc3c8b54b4289dba989cf1c2a5b8eb..615e1dcab36f052b6505bb65bd6bdbbe4a86de09 100644 (file)
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -2924,6 +2924,19 @@ static inline u64 cfs_rq_last_update_time(struct cfs_rq *cfs_rq)
 }
 #endif
 
+/*
+ * Synchronize entity load avg of dequeued entity without locking
+ * the previous rq.
+ */
+void sync_entity_load_avg(struct sched_entity *se)
+{
+       struct cfs_rq *cfs_rq = cfs_rq_of(se);
+       u64 last_update_time;
+
+       last_update_time = cfs_rq_last_update_time(cfs_rq);
+       __update_load_avg(last_update_time, cpu_of(rq_of(cfs_rq)), &se->avg, 0, 0, NULL);
+}
+
 /*
  * Task first catches up with cfs_rq, and then subtract
  * itself from the cfs_rq (task must be off the queue now).
@@ -2931,7 +2944,6 @@ static inline u64 cfs_rq_last_update_time(struct cfs_rq *cfs_rq)
 void remove_entity_load_avg(struct sched_entity *se)
 {
        struct cfs_rq *cfs_rq = cfs_rq_of(se);
-       u64 last_update_time;
 
        /*
         * Newly created task or never used group entity should not be removed
@@ -2940,9 +2952,7 @@ void remove_entity_load_avg(struct sched_entity *se)
        if (se->avg.last_update_time == 0)
                return;
 
-       last_update_time = cfs_rq_last_update_time(cfs_rq);
-
-       __update_load_avg(last_update_time, cpu_of(rq_of(cfs_rq)), &se->avg, 0, 0, NULL);
+       sync_entity_load_avg(se);
        atomic_long_add(se->avg.load_avg, &cfs_rq->removed_load_avg);
        atomic_long_add(se->avg.util_avg, &cfs_rq->removed_util_avg);
 }
@@ -5946,6 +5956,9 @@ static int wake_cap(struct task_struct *p, int cpu, int prev_cpu)
        if (max_cap - min_cap < max_cap >> 3)
                return 0;
 
+       /* Bring task utilization in sync with prev_cpu */
+       sync_entity_load_avg(&p->se);
+
        return min_cap * 1024 < task_util(p) * capacity_margin;
 }