Commit 3d30544f authored by Peter Zijlstra's avatar Peter Zijlstra Committed by Ingo Molnar
Browse files

sched/fair: Apply more PELT fixes 



One additional 'rule' for using update_cfs_rq_load_avg() is that one
should call update_tg_load_avg() if it returns true.

Add a bunch of comments to hopefully clarify some of the rules:

 o  You need to update cfs_rq _before_ any entity attach/detach,
    this is important, because while for mathmatical consisency this
    isn't strictly needed, it is required for the physical
    interpretation of the model, you attach/detach _now_.

 o  When you modify the cfs_rq avg, you have to then call
    update_tg_load_avg() in order to propagate changes upwards.

 o  (Fair) entities are always attached, switched_{to,from}_fair()
    deal with !fair. This directly follows from the definition of the
    cfs_rq averages, namely that they are a direct sum of all
    (runnable or blocked) entities on that rq.

It is the second rule that this patch enforces, but it adds comments
pertaining to all of them.

Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-kernel@vger.kernel.org
Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
parent 7dc603c9

kernel/sched/fair.c

+49 −4
Original line number Diff line number Diff line
@@ -692,6 +692,7 @@ void init_entity_runnable_average(struct sched_entity *se) 


static inline u64 cfs_rq_clock_task(struct cfs_rq *cfs_rq);

static int update_cfs_rq_load_avg(u64 now, struct cfs_rq *cfs_rq, bool update_freq);

static void update_tg_load_avg(struct cfs_rq *cfs_rq, int force);

static void attach_entity_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *se);



/*
@@ -725,6 +726,7 @@ void post_init_entity_util_avg(struct sched_entity *se) 
	struct sched_avg *sa = &se->avg;

	long cap = (long)(SCHED_CAPACITY_SCALE - cfs_rq->avg.util_avg) / 2;

	u64 now = cfs_rq_clock_task(cfs_rq);

	int tg_update;



	if (cap > 0) {

		if (cfs_rq->avg.util_avg != 0) {
@@ -757,8 +759,10 @@ void post_init_entity_util_avg(struct sched_entity *se) 
		}

	}



	update_cfs_rq_load_avg(now, cfs_rq, false);

	tg_update = update_cfs_rq_load_avg(now, cfs_rq, false);

	attach_entity_load_avg(cfs_rq, se);

	if (tg_update)

		update_tg_load_avg(cfs_rq, false);

}



#else /* !CONFIG_SMP */
@@ -768,6 +772,9 @@ void init_entity_runnable_average(struct sched_entity *se) 
void post_init_entity_util_avg(struct sched_entity *se)

{

}

static void update_tg_load_avg(struct cfs_rq *cfs_rq, int force)

{

}

#endif /* CONFIG_SMP */



/*
@@ -2912,7 +2919,23 @@ static inline void cfs_rq_util_change(struct cfs_rq *cfs_rq) 
	WRITE_ONCE(*ptr, res);					\

} while (0)



/* Group cfs_rq's load_avg is used for task_h_load and update_cfs_share */

/**

 * update_cfs_rq_load_avg - update the cfs_rq's load/util averages

 * @now: current time, as per cfs_rq_clock_task()

 * @cfs_rq: cfs_rq to update

 * @update_freq: should we call cfs_rq_util_change() or will the call do so

 *

 * The cfs_rq avg is the direct sum of all its entities (blocked and runnable)

 * avg. The immediate corollary is that all (fair) tasks must be attached, see

 * post_init_entity_util_avg().

 *

 * cfs_rq->avg is used for task_h_load() and update_cfs_share() for example.

 *

 * Returns true if the load decayed or we removed utilization. It is expected

 * that one calls update_tg_load_avg() on this condition, but after you've

 * modified the cfs_rq avg (attach/detach), such that we propagate the new

 * avg up.

 */

static inline int

update_cfs_rq_load_avg(u64 now, struct cfs_rq *cfs_rq, bool update_freq)

{
@@ -2967,6 +2990,14 @@ static inline void update_load_avg(struct sched_entity *se, int update_tg) 
		update_tg_load_avg(cfs_rq, 0);

}



/**

 * attach_entity_load_avg - attach this entity to its cfs_rq load avg

 * @cfs_rq: cfs_rq to attach to

 * @se: sched_entity to attach

 *

 * Must call update_cfs_rq_load_avg() before this, since we rely on

 * cfs_rq->avg.last_update_time being current.

 */

static void attach_entity_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *se)

{

	if (!sched_feat(ATTACH_AGE_LOAD))
@@ -2998,6 +3029,14 @@ skip_aging: 
	cfs_rq_util_change(cfs_rq);

}



/**

 * detach_entity_load_avg - detach this entity from its cfs_rq load avg

 * @cfs_rq: cfs_rq to detach from

 * @se: sched_entity to detach

 *

 * Must call update_cfs_rq_load_avg() before this, since we rely on

 * cfs_rq->avg.last_update_time being current.

 */

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)),
@@ -8404,6 +8443,7 @@ 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);

	u64 now = cfs_rq_clock_task(cfs_rq);

	int tg_update;



	if (!vruntime_normalized(p)) {

		/*
@@ -8415,8 +8455,10 @@ static void detach_task_cfs_rq(struct task_struct *p) 
	}



	/* Catch up with the cfs_rq and remove our load when we leave */

	update_cfs_rq_load_avg(now, cfs_rq, false);

	tg_update = update_cfs_rq_load_avg(now, cfs_rq, false);

	detach_entity_load_avg(cfs_rq, se);

	if (tg_update)

		update_tg_load_avg(cfs_rq, false);

}



static void attach_task_cfs_rq(struct task_struct *p)
@@ -8424,6 +8466,7 @@ static void attach_task_cfs_rq(struct task_struct *p) 
	struct sched_entity *se = &p->se;

	struct cfs_rq *cfs_rq = cfs_rq_of(se);

	u64 now = cfs_rq_clock_task(cfs_rq);

	int tg_update;



#ifdef CONFIG_FAIR_GROUP_SCHED

	/*
@@ -8434,8 +8477,10 @@ static void attach_task_cfs_rq(struct task_struct *p) 
#endif



	/* Synchronize task with its cfs_rq */

	update_cfs_rq_load_avg(now, cfs_rq, false);

	tg_update = update_cfs_rq_load_avg(now, cfs_rq, false);

	attach_entity_load_avg(cfs_rq, se);

	if (tg_update)

		update_tg_load_avg(cfs_rq, false);



	if (!vruntime_normalized(p))

		se->vruntime += cfs_rq->min_vruntime;

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