Date: Thu, 20 Aug 2015 03:17:21 +0200
From: Peter Zijlstra <peterz@infradead.org>
To: byungchul.park@lge.com
Cc: mingo@kernel.org, linux-kernel@vger.kernel.org, yuyang.du@intel.com
Subject: Re: [PATCH v3 0/5] sync a se with its cfs_rq when att(det)aching it
Message-ID: <20150820011721.GA3138@worktop.event.rightround.com>
References: <1439966836-11266-1-git-send-email-byungchul.park@lge.com>
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I did something like this on top.. please have a look at the XXX and
integrate.

---

--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -2664,8 +2664,8 @@ static inline u64 cfs_rq_clock_task(stru
 /* Group cfs_rq's load_avg is used for task_h_load and update_cfs_share */
 static inline int update_cfs_rq_load_avg(u64 now, struct cfs_rq *cfs_rq)
 {
-	int decayed;
 	struct sched_avg *sa = &cfs_rq->avg;
+	int decayed;
 
 	if (atomic_long_read(&cfs_rq->removed_load_avg)) {
 		long r = atomic_long_xchg(&cfs_rq->removed_load_avg, 0);
@@ -2695,15 +2695,16 @@ static inline int update_cfs_rq_load_avg
 static inline void update_load_avg(struct sched_entity *se, int update_tg)
 {
 	struct cfs_rq *cfs_rq = cfs_rq_of(se);
-	int cpu = cpu_of(rq_of(cfs_rq));
 	u64 now = cfs_rq_clock_task(cfs_rq);
+	int cpu = cpu_of(rq_of(cfs_rq));
 
 	/*
 	 * Track task load average for carrying it to new CPU after migrated, and
 	 * track group sched_entity load average for task_h_load calc in migration
 	 */
 	__update_load_avg(now, cpu, &se->avg,
-		se->on_rq * scale_load_down(se->load.weight), cfs_rq->curr == se, NULL);
+			  se->on_rq * scale_load_down(se->load.weight),
+			  cfs_rq->curr == se, NULL);
 
 	if (update_cfs_rq_load_avg(now, cfs_rq) && update_tg)
 		update_tg_load_avg(cfs_rq, 0);
@@ -2718,9 +2719,10 @@ static void attach_entity_load_avg(struc
 	 * update here. we have to update it with prev cfs_rq just before changing
 	 * se's cfs_rq, and get here soon.
 	 */
-	if (se->avg.last_update_time)
+	if (se->avg.last_update_time) {
 		__update_load_avg(cfs_rq->avg.last_update_time, cpu_of(rq_of(cfs_rq)),
-				&se->avg, 0, 0, NULL);
+				  &se->avg, 0, 0, NULL);
+	}
 
 	se->avg.last_update_time = cfs_rq->avg.last_update_time;
 	cfs_rq->avg.load_avg += se->avg.load_avg;
@@ -2732,17 +2734,13 @@ static void attach_entity_load_avg(struc
 static void detach_entity_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *se)
 {
 	__update_load_avg(cfs_rq->avg.last_update_time, cpu_of(rq_of(cfs_rq)),
-			&se->avg, se->on_rq * scale_load_down(se->load.weight),
-			cfs_rq->curr == se, NULL);
+			  &se->avg, se->on_rq * scale_load_down(se->load.weight),
+			  cfs_rq->curr == se, NULL);
 
-	cfs_rq->avg.load_avg =
-		max_t(long, cfs_rq->avg.load_avg - se->avg.load_avg, 0);
-	cfs_rq->avg.load_sum =
-		max_t(s64, cfs_rq->avg.load_sum - se->avg.load_sum, 0);
-	cfs_rq->avg.util_avg =
-		max_t(long, cfs_rq->avg.util_avg - se->avg.util_avg, 0);
-	cfs_rq->avg.util_sum =
-		max_t(s32, cfs_rq->avg.util_sum - se->avg.util_sum, 0);
+	cfs_rq->avg.load_avg = max_t(long, cfs_rq->avg.load_avg - se->avg.load_avg, 0);
+	cfs_rq->avg.load_sum = max_t(s64,  cfs_rq->avg.load_sum - se->avg.load_sum, 0);
+	cfs_rq->avg.util_avg = max_t(long, cfs_rq->avg.util_avg - se->avg.util_avg, 0);
+	cfs_rq->avg.util_sum = max_t(s32,  cfs_rq->avg.util_sum - se->avg.util_sum, 0);
 }
 
 /* Add the load generated by se into cfs_rq's load average */
@@ -2751,14 +2749,14 @@ enqueue_entity_load_avg(struct cfs_rq *c
 {
 	struct sched_avg *sa = &se->avg;
 	u64 now = cfs_rq_clock_task(cfs_rq);
-	int migrated = 0, decayed;
+	int migrated, decayed;
 
-	if (sa->last_update_time == 0)
-		migrated = 1;
-	else
+	migrated = !sa->last_update_time;
+	if (!migrated) {
 		__update_load_avg(now, cpu_of(rq_of(cfs_rq)), sa,
 			se->on_rq * scale_load_down(se->load.weight),
 			cfs_rq->curr == se, NULL);
+	}
 
 	decayed = update_cfs_rq_load_avg(now, cfs_rq);
 
@@ -2781,7 +2779,7 @@ dequeue_entity_load_avg(struct cfs_rq *c
 	cfs_rq->runnable_load_avg =
 		max_t(long, cfs_rq->runnable_load_avg - se->avg.load_avg, 0);
 	cfs_rq->runnable_load_sum =
-		max_t(s64, cfs_rq->runnable_load_sum - se->avg.load_sum, 0);
+		max_t(s64,  cfs_rq->runnable_load_sum - se->avg.load_sum, 0);
 }
 
 /*
@@ -2849,6 +2847,11 @@ static inline void
 dequeue_entity_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *se) {}
 static inline void remove_entity_load_avg(struct sched_entity *se) {}
 
+static inline void
+attach_entity_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *se) {}
+static inline void
+detach_entity_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *se) {}
+
 static inline int idle_balance(struct rq *rq)
 {
 	return 0;
@@ -7915,29 +7918,50 @@ prio_changed_fair(struct rq *rq, struct
 		check_preempt_curr(rq, p, 0);
 }
 
-static void detach_task_cfs_rq(struct task_struct *p, int queued)
+static inline bool vruntime_normalized(struct task_struct *p)
 {
+	int queued = task_on_rq_queued(p);
 	struct sched_entity *se = &p->se;
-	struct cfs_rq *cfs_rq = cfs_rq_of(se);
 
 	/*
-	 * Ensure the task's vruntime is normalized, so that after attaching
-	 * back it to a cfs_rq the enqueue_entity() will do the right thing.
-	 *
 	 * If it's queued, then the dequeue_entity(.flags=0) will already
-	 * have normalized the vruntime, if it's !queued, then only when
-	 * the task is sleeping it still has a non-normalized vruntime.
-	 *
+	 * have normalized the vruntime.
+	 */
+	if (queued)
+		return true;
+
+	/*
 	 * When !queued, vruntime of the task has usually NOT been normalized.
 	 * But there are some cases where it has already been normalized:
-	 *
-	 * - Moving a forked child which is waiting for being woken up by
+	 */
+
+	/*
+	 * - a forked child which is waiting for being woken up by
 	 *   wake_up_new_task().
-	 * - Moving a task which has been woken up by try_to_wake_up() and
+	 */
+	if (!se->sum_exec_runtime || p->state == TASK_WAKING)
+		return true;
+
+	/*
+	 * - a task which has been woken up by try_to_wake_up() and
 	 *   waiting for actually being woken up by sched_ttwu_pending().
+	 *
+	 * XXX this appears wrong!! check history, 
+	 * we appear to always set queued and RUNNING under the same lock instance
+	 * might be from before TASK_WAKING ?
 	 */
-	if (!queued && p->state != TASK_RUNNING &&
-	    se->sum_exec_runtime && p->state != TASK_WAKING) {
+	if (p->state == TASK_RUNNING)
+		return true;
+
+	return false;
+}
+
+static void detach_task_cfs_rq(struct task_struct *p)
+{
+	struct sched_entity *se = &p->se;
+	struct cfs_rq *cfs_rq = cfs_rq_of(se);
+
+	if (!vruntime_normalized(p)) {
 		/*
 		 * Fix up our vruntime so that the current sleep doesn't
 		 * cause 'unlimited' sleep bonus.
@@ -7946,10 +7970,8 @@ static void detach_task_cfs_rq(struct ta
 		se->vruntime -= cfs_rq->min_vruntime;
 	}
 
-#ifdef CONFIG_SMP
 	/* Catch up with the cfs_rq and remove our load when we leave */
 	detach_entity_load_avg(cfs_rq, se);
-#endif
 }
 
 static void attach_task_cfs_rq(struct task_struct *p, int queued)
@@ -7965,49 +7987,23 @@ static void attach_task_cfs_rq(struct ta
 	se->depth = se->parent ? se->parent->depth + 1 : 0;
 #endif
 
-#ifdef CONFIG_SMP
 	/* synchronize task with its cfs_rq */
 	attach_entity_load_avg(cfs_rq, se);
-#endif
 
-	/*
-	 * Ensure the task has a non-normalized vruntime when attaching it
-	 * to a cfs_rq, so that enqueue_entity() at wake-up time will do
-	 * the right thing.
-	 *
-	 * If it's queued, then the enqueue_entity(.flags=0) makes the task
-	 * has non-normalized vruntime, if it's !queued, then it still has
-	 * a normalized vruntime.
-	 *
-	 * When !queued, a task usually should have a non-normalized vruntime
-	 * after being attached to a cfs_rq. But there are some cases where
-	 * we should keep it normalized:
-	 *
-	 * - Moving a forked child which is waiting for being woken up by
-	 *   wake_up_new_task().
-	 * - Moving a task which has been woken up by try_to_wake_up() and
-	 *   waiting for actually being woken up by sched_ttwu_pending().
-	 */
-	if (!queued && p->state != TASK_RUNNING &&
-	    se->sum_exec_runtime && p->state != TASK_WAKING)
+	if (!vruntime_normalized(p))
 		se->vruntime += cfs_rq->min_vruntime;
 }
 
 static void switched_from_fair(struct rq *rq, struct task_struct *p)
 {
-	detach_task_cfs_rq(p, task_on_rq_queued(p));
+	detach_task_cfs_rq(p);
 }
 
-/*
- * We switched to the sched_fair class.
- */
 static void switched_to_fair(struct rq *rq, struct task_struct *p)
 {
-	int queued = task_on_rq_queued(p);
-
-	attach_task_cfs_rq(p, queued);
+	attach_task_cfs_rq(p);
 
-	if (queued) {
+	if (task_on_rq_queued(p)) {
 		/*
 		 * We were most likely switched from sched_rt, so
 		 * kick off the schedule if running, otherwise just see
@@ -8056,8 +8052,7 @@ static void task_move_group_fair(struct
 {
 	detach_task_cfs_rq(p, queued);
 	set_task_rq(p, task_cpu(p));
-
-	/* tell se's cfs_rq has been changed */
+	/* tell se's cfs_rq has been changed -- migrated */
 	p->se.avg.last_update_time = 0;
 	attach_task_cfs_rq(p, queued);
 }
--
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