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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>
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@ -692,6 +692,7 @@ void init_entity_runnable_average(struct sched_entity *se)
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static inline u64 cfs_rq_clock_task(struct cfs_rq *cfs_rq);
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static int update_cfs_rq_load_avg(u64 now, struct cfs_rq *cfs_rq, bool update_freq);
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static void update_tg_load_avg(struct cfs_rq *cfs_rq, int force);
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static void attach_entity_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *se);
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/*
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@ -725,6 +726,7 @@ void post_init_entity_util_avg(struct sched_entity *se)
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struct sched_avg *sa = &se->avg;
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long cap = (long)(SCHED_CAPACITY_SCALE - cfs_rq->avg.util_avg) / 2;
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u64 now = cfs_rq_clock_task(cfs_rq);
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int tg_update;
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if (cap > 0) {
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if (cfs_rq->avg.util_avg != 0) {
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@ -757,8 +759,10 @@ void post_init_entity_util_avg(struct sched_entity *se)
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}
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}
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update_cfs_rq_load_avg(now, cfs_rq, false);
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tg_update = update_cfs_rq_load_avg(now, cfs_rq, false);
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attach_entity_load_avg(cfs_rq, se);
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if (tg_update)
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update_tg_load_avg(cfs_rq, false);
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}
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#else /* !CONFIG_SMP */
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@ -768,6 +772,9 @@ void init_entity_runnable_average(struct sched_entity *se)
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void post_init_entity_util_avg(struct sched_entity *se)
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{
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}
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static void update_tg_load_avg(struct cfs_rq *cfs_rq, int force)
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{
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}
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#endif /* CONFIG_SMP */
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/*
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@ -2912,7 +2919,23 @@ static inline void cfs_rq_util_change(struct cfs_rq *cfs_rq)
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WRITE_ONCE(*ptr, res); \
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} while (0)
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/* Group cfs_rq's load_avg is used for task_h_load and update_cfs_share */
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/**
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* update_cfs_rq_load_avg - update the cfs_rq's load/util averages
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* @now: current time, as per cfs_rq_clock_task()
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* @cfs_rq: cfs_rq to update
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* @update_freq: should we call cfs_rq_util_change() or will the call do so
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*
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* The cfs_rq avg is the direct sum of all its entities (blocked and runnable)
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* avg. The immediate corollary is that all (fair) tasks must be attached, see
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* post_init_entity_util_avg().
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*
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* cfs_rq->avg is used for task_h_load() and update_cfs_share() for example.
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*
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* Returns true if the load decayed or we removed utilization. It is expected
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* that one calls update_tg_load_avg() on this condition, but after you've
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* modified the cfs_rq avg (attach/detach), such that we propagate the new
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* avg up.
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*/
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static inline int
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update_cfs_rq_load_avg(u64 now, struct cfs_rq *cfs_rq, bool update_freq)
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{
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@ -2967,6 +2990,14 @@ static inline void update_load_avg(struct sched_entity *se, int update_tg)
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update_tg_load_avg(cfs_rq, 0);
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}
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/**
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* attach_entity_load_avg - attach this entity to its cfs_rq load avg
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* @cfs_rq: cfs_rq to attach to
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* @se: sched_entity to attach
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*
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* Must call update_cfs_rq_load_avg() before this, since we rely on
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* cfs_rq->avg.last_update_time being current.
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*/
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static void attach_entity_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *se)
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{
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if (!sched_feat(ATTACH_AGE_LOAD))
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@ -2998,6 +3029,14 @@ skip_aging:
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cfs_rq_util_change(cfs_rq);
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}
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/**
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* detach_entity_load_avg - detach this entity from its cfs_rq load avg
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* @cfs_rq: cfs_rq to detach from
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* @se: sched_entity to detach
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*
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* Must call update_cfs_rq_load_avg() before this, since we rely on
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* cfs_rq->avg.last_update_time being current.
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*/
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static void detach_entity_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *se)
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{
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__update_load_avg(cfs_rq->avg.last_update_time, cpu_of(rq_of(cfs_rq)),
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@ -8404,6 +8443,7 @@ static void detach_task_cfs_rq(struct task_struct *p)
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struct sched_entity *se = &p->se;
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struct cfs_rq *cfs_rq = cfs_rq_of(se);
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u64 now = cfs_rq_clock_task(cfs_rq);
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int tg_update;
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if (!vruntime_normalized(p)) {
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/*
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@ -8415,8 +8455,10 @@ static void detach_task_cfs_rq(struct task_struct *p)
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}
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/* Catch up with the cfs_rq and remove our load when we leave */
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update_cfs_rq_load_avg(now, cfs_rq, false);
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tg_update = update_cfs_rq_load_avg(now, cfs_rq, false);
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detach_entity_load_avg(cfs_rq, se);
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if (tg_update)
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update_tg_load_avg(cfs_rq, false);
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}
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static void attach_task_cfs_rq(struct task_struct *p)
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@ -8424,6 +8466,7 @@ static void attach_task_cfs_rq(struct task_struct *p)
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struct sched_entity *se = &p->se;
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struct cfs_rq *cfs_rq = cfs_rq_of(se);
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u64 now = cfs_rq_clock_task(cfs_rq);
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int tg_update;
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#ifdef CONFIG_FAIR_GROUP_SCHED
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/*
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@ -8434,8 +8477,10 @@ static void attach_task_cfs_rq(struct task_struct *p)
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#endif
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/* Synchronize task with its cfs_rq */
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update_cfs_rq_load_avg(now, cfs_rq, false);
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tg_update = update_cfs_rq_load_avg(now, cfs_rq, false);
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attach_entity_load_avg(cfs_rq, se);
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if (tg_update)
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update_tg_load_avg(cfs_rq, false);
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if (!vruntime_normalized(p))
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se->vruntime += cfs_rq->min_vruntime;
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