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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: Peter 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: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Peter Zijlstra 2016-06-21 14:27:50 +02:00 committed by Ingo Molnar
parent 7dc603c902
commit 3d30544f02
1 changed files with 49 additions and 4 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

53
kernel/sched/fair.c
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@ -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;