[PATCH RFC v2 0/10] sched,fair: flatten CPU controller runqueues

[PATCH RFC v2 0/10] sched,fair: flatten CPU controller runqueues

[Rik van Riel]

The current implementation of the CPU controller uses hierarchical
runqueues, where on wakeup a task is enqueued on its group's runqueue,
the group is enqueued on the runqueue of the group above it, etc.

This increases a fairly large amount of overhead for workloads that
do a lot of wakeups a second, especially given that the default systemd
hierarchy is 2 or 3 levels deep.

This patch series is an attempt at reducing that overhead, by placing
all the tasks on the same runqueue, and scaling the task priority by
the priority of the group, which is calculated periodically.

This patch series still has a number of TODO items:
- Clean up the code, and fix compilation without CONFIG_FAIR_GROUP_SCHED.
- Remove some more now unused code.
- Figure out a performance regression with our web server workload.
  I have fixed the schbench issue, now I need to find the less obvious
  stuff causing an increased number of involuntary preemptions...
- Reimplement CONFIG_CFS_BANDWIDTH.

Plan for the CONFIG_CFS_BANDWIDTH reimplementation:
- When a cgroup gets throttled, mark the cgroup and its children
  as throttled.
- When pick_next_entity finds a task that is on a throttled cgroup,
  stash it on the cgroup runqueue (which is not used for runnable
  tasks any more). Leave the vruntime unchanged, and adjust that
  runqueue's vruntime to be that of the left-most task.
- When a cgroup gets unthrottled, and has tasks on it, place it on
  a vruntime ordered heap separate from the main runqueue.
- Have pick_next_task_fair grab one task off that heap every time it
  is called, and the min vruntime of that heap is lower than the
  vruntime of the CPU's cfs_rq (or the CPU has no other runnable tasks).
- Place that selected task on the CPU's cfs_rq, renormalizing its
  vruntime with the GENTLE_FAIR_SLEEPERS logic. That should help
  interleave the already runnable tasks with the recently unthrottled
  group, and prevent thundering herd issues.
- If the group gets throttled again before all of its task had a chance
  to run, vruntime sorting ensures all the tasks in the throttled cgroup
  get a chance to run over time.

Changes from v1:
- use task_se_h_weight instead of task_se_h_load in calc_delta_fair
  and sched_slice, this seems to improve performance a little, but
  I still have some remaining regression to chase with our web server
  workload
- implement a number of the changes suggested by Dietmar Eggemann
  (still holding out for a better name for group_cfs_rq_of_parent)

This series applies on top of 5.2-rc6.

 include/linux/sched.h |    6 
 kernel/sched/core.c   |    2 
 kernel/sched/debug.c  |   15 -
 kernel/sched/fair.c   |  746 +++++++++++++++++++++-----------------------------
 kernel/sched/pelt.c   |   53 +--
 kernel/sched/pelt.h   |    2 
 kernel/sched/sched.h  |   10 
 7 files changed, 346 insertions(+), 488 deletions(-)

[PATCH 01/10] sched: introduce task_se_h_load helper

[Rik van Riel]

Sometimes the hierarchical load of a sched_entity needs to be calculated.
Rename task_h_load to task_se_h_load, and directly pass a sched_entity to
that function.

Move the function declaration up above where it will be used later.

No functional changes.

Signed-off-by: Rik van Riel <riel@surriel.com>
---
 kernel/sched/fair.c | 28 ++++++++++++++--------------
 1 file changed, 14 insertions(+), 14 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index f35930f5e528..eadf9a96b3e1 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -242,6 +242,7 @@ static u64 __calc_delta(u64 delta_exec, unsigned long weight, struct load_weight
 
 
 const struct sched_class fair_sched_class;
+static unsigned long task_se_h_load(struct sched_entity *se);
 
 /**************************************************************
  * CFS operations on generic schedulable entities:
@@ -706,7 +707,6 @@ static u64 sched_vslice(struct cfs_rq *cfs_rq, struct sched_entity *se)
 #ifdef CONFIG_SMP
 
 static int select_idle_sibling(struct task_struct *p, int prev_cpu, int cpu);
-static unsigned long task_h_load(struct task_struct *p);
 static unsigned long capacity_of(int cpu);
 
 /* Give new sched_entity start runnable values to heavy its load in infant time */
@@ -1668,7 +1668,7 @@ static void task_numa_compare(struct task_numa_env *env,
 	/*
 	 * In the overloaded case, try and keep the load balanced.
 	 */
-	load = task_h_load(env->p) - task_h_load(cur);
+	load = task_se_h_load(env->p->se) - task_se_h_load(cur->se);
 	if (!load)
 		goto assign;
 
@@ -1706,7 +1706,7 @@ static void task_numa_find_cpu(struct task_numa_env *env,
 	bool maymove = false;
 	int cpu;
 
-	load = task_h_load(env->p);
+	load = task_se_h_load(env->p->se);
 	dst_load = env->dst_stats.load + load;
 	src_load = env->src_stats.load - load;
 
@@ -3389,7 +3389,7 @@ static inline void add_tg_cfs_propagate(struct cfs_rq *cfs_rq, long runnable_sum
  * 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.
+ * cfs_rq->avg is used for task_se_h_load() and update_cfs_share() for example.
  *
  * Returns true if the load decayed or we removed load.
  *
@@ -3522,7 +3522,7 @@ static inline void update_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *s
 
 	/*
 	 * 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
+	 * track group sched_entity load average for task_se_h_load calc in migration
 	 */
 	if (se->avg.last_update_time && !(flags & SKIP_AGE_LOAD))
 		__update_load_avg_se(now, cfs_rq, se);
@@ -3751,7 +3751,7 @@ static inline void update_misfit_status(struct task_struct *p, struct rq *rq)
 		return;
 	}
 
-	rq->misfit_task_load = task_h_load(p);
+	rq->misfit_task_load = task_se_h_load(&p->se);
 }
 
 #else /* CONFIG_SMP */
@@ -5739,7 +5739,7 @@ wake_affine_weight(struct sched_domain *sd, struct task_struct *p,
 	this_eff_load = target_load(this_cpu, sd->wake_idx);
 
 	if (sync) {
-		unsigned long current_load = task_h_load(current);
+		unsigned long current_load = task_se_h_load(&current->se);
 
 		if (current_load > this_eff_load)
 			return this_cpu;
@@ -5747,7 +5747,7 @@ wake_affine_weight(struct sched_domain *sd, struct task_struct *p,
 		this_eff_load -= current_load;
 	}
 
-	task_load = task_h_load(p);
+	task_load = task_se_h_load(&p->se);
 
 	this_eff_load += task_load;
 	if (sched_feat(WA_BIAS))
@@ -7600,7 +7600,7 @@ static int detach_tasks(struct lb_env *env)
 		if (!can_migrate_task(p, env))
 			goto next;
 
-		load = task_h_load(p);
+		load = task_se_h_load(&p->se);
 
 		if (sched_feat(LB_MIN) && load < 16 && !env->sd->nr_balance_failed)
 			goto next;
@@ -7833,12 +7833,12 @@ static void update_cfs_rq_h_load(struct cfs_rq *cfs_rq)
 	}
 }
 
-static unsigned long task_h_load(struct task_struct *p)
+static unsigned long task_se_h_load(struct sched_entity *se)
 {
-	struct cfs_rq *cfs_rq = task_cfs_rq(p);
+	struct cfs_rq *cfs_rq = cfs_rq_of(se);
 
 	update_cfs_rq_h_load(cfs_rq);
-	return div64_ul(p->se.avg.load_avg * cfs_rq->h_load,
+	return div64_ul(se->avg.load_avg * cfs_rq->h_load,
 			cfs_rq_load_avg(cfs_rq) + 1);
 }
 #else
@@ -7865,9 +7865,9 @@ static inline void update_blocked_averages(int cpu)
 	rq_unlock_irqrestore(rq, &rf);
 }
 
-static unsigned long task_h_load(struct task_struct *p)
+static unsigned long task_se_h_load(struct sched_entity *se)
 {
-	return p->se.avg.load_avg;
+	return se->avg.load_avg;
 }
 #endif
 
-- 
2.20.1

[PATCH 02/10] sched: change /proc/sched_debug fields

[Rik van Riel]

Remove some fields from /proc/sched_debug that are removed from
sched_entity in a subsequent patch, and add h_load, which comes in
very handy to debug CPU controller weight distribution.

Signed-off-by: Rik van Riel <riel@surriel.com>
---
 kernel/sched/debug.c | 11 ++---------
 1 file changed, 2 insertions(+), 9 deletions(-)

diff --git a/kernel/sched/debug.c b/kernel/sched/debug.c
index 14c6a8716ba1..f6beaca97a09 100644
--- a/kernel/sched/debug.c
+++ b/kernel/sched/debug.c
@@ -416,11 +416,9 @@ static void print_cfs_group_stats(struct seq_file *m, int cpu, struct task_group
 	}
 
 	P(se->load.weight);
-	P(se->runnable_weight);
 #ifdef CONFIG_SMP
 	P(se->avg.load_avg);
 	P(se->avg.util_avg);
-	P(se->avg.runnable_load_avg);
 #endif
 
 #undef PN_SCHEDSTAT
@@ -538,7 +536,6 @@ void print_cfs_rq(struct seq_file *m, int cpu, struct cfs_rq *cfs_rq)
 	SEQ_printf(m, "  .%-30s: %d\n", "nr_running", cfs_rq->nr_running);
 	SEQ_printf(m, "  .%-30s: %ld\n", "load", cfs_rq->load.weight);
 #ifdef CONFIG_SMP
-	SEQ_printf(m, "  .%-30s: %ld\n", "runnable_weight", cfs_rq->runnable_weight);
 	SEQ_printf(m, "  .%-30s: %lu\n", "load_avg",
 			cfs_rq->avg.load_avg);
 	SEQ_printf(m, "  .%-30s: %lu\n", "runnable_load_avg",
@@ -547,17 +544,15 @@ void print_cfs_rq(struct seq_file *m, int cpu, struct cfs_rq *cfs_rq)
 			cfs_rq->avg.util_avg);
 	SEQ_printf(m, "  .%-30s: %u\n", "util_est_enqueued",
 			cfs_rq->avg.util_est.enqueued);
-	SEQ_printf(m, "  .%-30s: %ld\n", "removed.load_avg",
-			cfs_rq->removed.load_avg);
 	SEQ_printf(m, "  .%-30s: %ld\n", "removed.util_avg",
 			cfs_rq->removed.util_avg);
-	SEQ_printf(m, "  .%-30s: %ld\n", "removed.runnable_sum",
-			cfs_rq->removed.runnable_sum);
 #ifdef CONFIG_FAIR_GROUP_SCHED
 	SEQ_printf(m, "  .%-30s: %lu\n", "tg_load_avg_contrib",
 			cfs_rq->tg_load_avg_contrib);
 	SEQ_printf(m, "  .%-30s: %ld\n", "tg_load_avg",
 			atomic_long_read(&cfs_rq->tg->load_avg));
+	SEQ_printf(m, "  .%-30s: %lu\n", "h_load",
+			cfs_rq->h_load);
 #endif
 #endif
 #ifdef CONFIG_CFS_BANDWIDTH
@@ -961,10 +956,8 @@ void proc_sched_show_task(struct task_struct *p, struct pid_namespace *ns,
 		   "nr_involuntary_switches", (long long)p->nivcsw);
 
 	P(se.load.weight);
-	P(se.runnable_weight);
 #ifdef CONFIG_SMP
 	P(se.avg.load_sum);
-	P(se.avg.runnable_load_sum);
 	P(se.avg.util_sum);
 	P(se.avg.load_avg);
 	P(se.avg.runnable_load_avg);
-- 
2.20.1

[PATCH 03/10] sched,fair: redefine runnable_load_avg as the sum of task_h_load

[Rik van Riel]

The runnable_load magic is used to quickly propagate information about
runnable tasks up the hierarchy of runqueues. The runnable_load_avg is
mostly used for the load balancing code, which only examines the value at
the root cfs_rq.

Redefine the root cfs_rq runnable_load_avg to be the sum of task_h_loads
of the runnable tasks. This works because the hierarchical runnable_load of
a task is already equal to the task_se_h_load today. This provides enough
information to the load balancer.

The runnable_load_avg of the cgroup cfs_rqs does not appear to be
used for anything, so don't bother calculating those.

This removes one of the things that the code currently traverses the
cgroup hierarchy for, and getting rid of it brings us one step closer
to a flat runqueue for the CPU controller.

Signed-off-by: Rik van Riel <riel@surriel.com>
---
 include/linux/sched.h |   3 +-
 kernel/sched/core.c   |   2 -
 kernel/sched/debug.c  |   1 +
 kernel/sched/fair.c   | 125 +++++++++++++-----------------------------
 kernel/sched/pelt.c   |  49 ++++++-----------
 kernel/sched/sched.h  |   6 --
 6 files changed, 55 insertions(+), 131 deletions(-)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 11837410690f..f5bb6948e40c 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -391,7 +391,6 @@ struct util_est {
 struct sched_avg {
 	u64				last_update_time;
 	u64				load_sum;
-	u64				runnable_load_sum;
 	u32				util_sum;
 	u32				period_contrib;
 	unsigned long			load_avg;
@@ -439,7 +438,6 @@ struct sched_statistics {
 struct sched_entity {
 	/* For load-balancing: */
 	struct load_weight		load;
-	unsigned long			runnable_weight;
 	struct rb_node			run_node;
 	struct list_head		group_node;
 	unsigned int			on_rq;
@@ -455,6 +453,7 @@ struct sched_entity {
 
 #ifdef CONFIG_FAIR_GROUP_SCHED
 	int				depth;
+	unsigned long			enqueued_h_load;
 	struct sched_entity		*parent;
 	/* rq on which this entity is (to be) queued: */
 	struct cfs_rq			*cfs_rq;
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 874c427742a9..fbd96900f715 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -744,7 +744,6 @@ static void set_load_weight(struct task_struct *p, bool update_load)
 	if (task_has_idle_policy(p)) {
 		load->weight = scale_load(WEIGHT_IDLEPRIO);
 		load->inv_weight = WMULT_IDLEPRIO;
-		p->se.runnable_weight = load->weight;
 		return;
 	}
 
@@ -757,7 +756,6 @@ static void set_load_weight(struct task_struct *p, bool update_load)
 	} else {
 		load->weight = scale_load(sched_prio_to_weight[prio]);
 		load->inv_weight = sched_prio_to_wmult[prio];
-		p->se.runnable_weight = load->weight;
 	}
 }
 
diff --git a/kernel/sched/debug.c b/kernel/sched/debug.c
index f6beaca97a09..cefc1b171c0b 100644
--- a/kernel/sched/debug.c
+++ b/kernel/sched/debug.c
@@ -962,6 +962,7 @@ void proc_sched_show_task(struct task_struct *p, struct pid_namespace *ns,
 	P(se.avg.load_avg);
 	P(se.avg.runnable_load_avg);
 	P(se.avg.util_avg);
+	P(se.enqueued_h_load);
 	P(se.avg.last_update_time);
 	P(se.avg.util_est.ewma);
 	P(se.avg.util_est.enqueued);
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index eadf9a96b3e1..860708b687a7 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -723,9 +723,7 @@ void init_entity_runnable_average(struct sched_entity *se)
 	 * nothing has been attached to the task group yet.
 	 */
 	if (entity_is_task(se))
-		sa->runnable_load_avg = sa->load_avg = scale_load_down(se->load.weight);
-
-	se->runnable_weight = se->load.weight;
+		sa->load_avg = scale_load_down(se->load.weight);
 
 	/* when this task enqueue'ed, it will contribute to its cfs_rq's load_avg */
 }
@@ -2766,20 +2764,39 @@ account_entity_dequeue(struct cfs_rq *cfs_rq, struct sched_entity *se)
 static inline void
 enqueue_runnable_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *se)
 {
-	cfs_rq->runnable_weight += se->runnable_weight;
+	if (entity_is_task(se)) {
+		struct cfs_rq *root_cfs_rq = &cfs_rq->rq->cfs;
+		se->enqueued_h_load = task_se_h_load(se);
 
-	cfs_rq->avg.runnable_load_avg += se->avg.runnable_load_avg;
-	cfs_rq->avg.runnable_load_sum += se_runnable(se) * se->avg.runnable_load_sum;
+		root_cfs_rq->avg.runnable_load_avg += se->enqueued_h_load;
+	}
 }
 
 static inline void
 dequeue_runnable_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *se)
 {
-	cfs_rq->runnable_weight -= se->runnable_weight;
+	if (entity_is_task(se)) {
+		struct cfs_rq *root_cfs_rq = &cfs_rq->rq->cfs;
+		sub_positive(&root_cfs_rq->avg.runnable_load_avg,
+					se->enqueued_h_load);
+	}
+}
+
+static inline void
+update_runnable_load_avg(struct sched_entity *se)
+{
+	struct cfs_rq *root_cfs_rq = &cfs_rq_of(se)->rq->cfs;
+	long new_h_load, delta;
+
+	SCHED_WARN_ON(!entity_is_task(se));
+
+	if (!se->on_rq)
+		return;
 
-	sub_positive(&cfs_rq->avg.runnable_load_avg, se->avg.runnable_load_avg);
-	sub_positive(&cfs_rq->avg.runnable_load_sum,
-		     se_runnable(se) * se->avg.runnable_load_sum);
+	new_h_load = task_se_h_load(se);
+	delta = new_h_load - se->enqueued_h_load;
+	root_cfs_rq->avg.runnable_load_avg += delta;
+	se->enqueued_h_load = new_h_load;
 }
 
 static inline void
@@ -2807,7 +2824,7 @@ dequeue_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *se) { }
 #endif
 
 static void reweight_entity(struct cfs_rq *cfs_rq, struct sched_entity *se,
-			    unsigned long weight, unsigned long runnable)
+			    unsigned long weight)
 {
 	if (se->on_rq) {
 		/* commit outstanding execution time */
@@ -2818,7 +2835,6 @@ static void reweight_entity(struct cfs_rq *cfs_rq, struct sched_entity *se,
 	}
 	dequeue_load_avg(cfs_rq, se);
 
-	se->runnable_weight = runnable;
 	update_load_set(&se->load, weight);
 
 #ifdef CONFIG_SMP
@@ -2826,8 +2842,6 @@ static void reweight_entity(struct cfs_rq *cfs_rq, struct sched_entity *se,
 		u32 divider = LOAD_AVG_MAX - 1024 + se->avg.period_contrib;
 
 		se->avg.load_avg = div_u64(se_weight(se) * se->avg.load_sum, divider);
-		se->avg.runnable_load_avg =
-			div_u64(se_runnable(se) * se->avg.runnable_load_sum, divider);
 	} while (0);
 #endif
 
@@ -2845,7 +2859,7 @@ void reweight_task(struct task_struct *p, int prio)
 	struct load_weight *load = &se->load;
 	unsigned long weight = scale_load(sched_prio_to_weight[prio]);
 
-	reweight_entity(cfs_rq, se, weight, weight);
+	reweight_entity(cfs_rq, se, weight);
 	load->inv_weight = sched_prio_to_wmult[prio];
 }
 
@@ -2958,49 +2972,6 @@ static long calc_group_shares(struct cfs_rq *cfs_rq)
 	return clamp_t(long, shares, MIN_SHARES, tg_shares);
 }
 
-/*
- * This calculates the effective runnable weight for a group entity based on
- * the group entity weight calculated above.
- *
- * Because of the above approximation (2), our group entity weight is
- * an load_avg based ratio (3). This means that it includes blocked load and
- * does not represent the runnable weight.
- *
- * Approximate the group entity's runnable weight per ratio from the group
- * runqueue:
- *
- *					     grq->avg.runnable_load_avg
- *   ge->runnable_weight = ge->load.weight * -------------------------- (7)
- *						 grq->avg.load_avg
- *
- * However, analogous to above, since the avg numbers are slow, this leads to
- * transients in the from-idle case. Instead we use:
- *
- *   ge->runnable_weight = ge->load.weight *
- *
- *		max(grq->avg.runnable_load_avg, grq->runnable_weight)
- *		-----------------------------------------------------	(8)
- *		      max(grq->avg.load_avg, grq->load.weight)
- *
- * Where these max() serve both to use the 'instant' values to fix the slow
- * from-idle and avoid the /0 on to-idle, similar to (6).
- */
-static long calc_group_runnable(struct cfs_rq *cfs_rq, long shares)
-{
-	long runnable, load_avg;
-
-	load_avg = max(cfs_rq->avg.load_avg,
-		       scale_load_down(cfs_rq->load.weight));
-
-	runnable = max(cfs_rq->avg.runnable_load_avg,
-		       scale_load_down(cfs_rq->runnable_weight));
-
-	runnable *= shares;
-	if (load_avg)
-		runnable /= load_avg;
-
-	return clamp_t(long, runnable, MIN_SHARES, shares);
-}
 #endif /* CONFIG_SMP */
 
 static inline int throttled_hierarchy(struct cfs_rq *cfs_rq);
@@ -3012,25 +2983,24 @@ static inline int throttled_hierarchy(struct cfs_rq *cfs_rq);
 static void update_cfs_group(struct sched_entity *se)
 {
 	struct cfs_rq *gcfs_rq = group_cfs_rq(se);
-	long shares, runnable;
+	long shares;
 
-	if (!gcfs_rq)
+	if (!gcfs_rq) {
+		update_runnable_load_avg(se);
 		return;
+	}
 
 	if (throttled_hierarchy(gcfs_rq))
 		return;
 
 #ifndef CONFIG_SMP
-	runnable = shares = READ_ONCE(gcfs_rq->tg->shares);
-
 	if (likely(se->load.weight == shares))
 		return;
 #else
 	shares   = calc_group_shares(gcfs_rq);
-	runnable = calc_group_runnable(gcfs_rq, shares);
 #endif
 
-	reweight_entity(cfs_rq_of(se), se, shares, runnable);
+	reweight_entity(cfs_rq_of(se), se, shares);
 }
 
 #else /* CONFIG_FAIR_GROUP_SCHED */
@@ -3243,8 +3213,8 @@ static inline void
 update_tg_cfs_runnable(struct cfs_rq *cfs_rq, struct sched_entity *se, struct cfs_rq *gcfs_rq)
 {
 	long delta_avg, running_sum, runnable_sum = gcfs_rq->prop_runnable_sum;
-	unsigned long runnable_load_avg, load_avg;
-	u64 runnable_load_sum, load_sum = 0;
+	unsigned long load_avg;
+	u64 load_sum = 0;
 	s64 delta_sum;
 
 	if (!runnable_sum)
@@ -3292,19 +3262,6 @@ update_tg_cfs_runnable(struct cfs_rq *cfs_rq, struct sched_entity *se, struct cf
 	se->avg.load_avg = load_avg;
 	add_positive(&cfs_rq->avg.load_avg, delta_avg);
 	add_positive(&cfs_rq->avg.load_sum, delta_sum);
-
-	runnable_load_sum = (s64)se_runnable(se) * runnable_sum;
-	runnable_load_avg = div_s64(runnable_load_sum, LOAD_AVG_MAX);
-	delta_sum = runnable_load_sum - se_weight(se) * se->avg.runnable_load_sum;
-	delta_avg = runnable_load_avg - se->avg.runnable_load_avg;
-
-	se->avg.runnable_load_sum = runnable_sum;
-	se->avg.runnable_load_avg = runnable_load_avg;
-
-	if (se->on_rq) {
-		add_positive(&cfs_rq->avg.runnable_load_avg, delta_avg);
-		add_positive(&cfs_rq->avg.runnable_load_sum, delta_sum);
-	}
 }
 
 static inline void add_tg_cfs_propagate(struct cfs_rq *cfs_rq, long runnable_sum)
@@ -3399,7 +3356,7 @@ static inline void add_tg_cfs_propagate(struct cfs_rq *cfs_rq, long runnable_sum
 static inline int
 update_cfs_rq_load_avg(u64 now, struct cfs_rq *cfs_rq)
 {
-	unsigned long removed_load = 0, removed_util = 0, removed_runnable_sum = 0;
+	unsigned long removed_load = 0, removed_util = 0;
 	struct sched_avg *sa = &cfs_rq->avg;
 	int decayed = 0;
 
@@ -3410,7 +3367,6 @@ update_cfs_rq_load_avg(u64 now, struct cfs_rq *cfs_rq)
 		raw_spin_lock(&cfs_rq->removed.lock);
 		swap(cfs_rq->removed.util_avg, removed_util);
 		swap(cfs_rq->removed.load_avg, removed_load);
-		swap(cfs_rq->removed.runnable_sum, removed_runnable_sum);
 		cfs_rq->removed.nr = 0;
 		raw_spin_unlock(&cfs_rq->removed.lock);
 
@@ -3422,8 +3378,6 @@ update_cfs_rq_load_avg(u64 now, struct cfs_rq *cfs_rq)
 		sub_positive(&sa->util_avg, r);
 		sub_positive(&sa->util_sum, r * divider);
 
-		add_tg_cfs_propagate(cfs_rq, -(long)removed_runnable_sum);
-
 		decayed = 1;
 	}
 
@@ -3477,8 +3431,6 @@ static void attach_entity_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *s
 			div_u64(se->avg.load_avg * se->avg.load_sum, se_weight(se));
 	}
 
-	se->avg.runnable_load_sum = se->avg.load_sum;
-
 	enqueue_load_avg(cfs_rq, se);
 	cfs_rq->avg.util_avg += se->avg.util_avg;
 	cfs_rq->avg.util_sum += se->avg.util_sum;
@@ -7735,9 +7687,6 @@ static inline bool cfs_rq_is_decayed(struct cfs_rq *cfs_rq)
 	if (cfs_rq->avg.util_sum)
 		return false;
 
-	if (cfs_rq->avg.runnable_load_sum)
-		return false;
-
 	return true;
 }
 
diff --git a/kernel/sched/pelt.c b/kernel/sched/pelt.c
index befce29bd882..190797e421dd 100644
--- a/kernel/sched/pelt.c
+++ b/kernel/sched/pelt.c
@@ -106,7 +106,7 @@ static u32 __accumulate_pelt_segments(u64 periods, u32 d1, u32 d3)
  */
 static __always_inline u32
 accumulate_sum(u64 delta, struct sched_avg *sa,
-	       unsigned long load, unsigned long runnable, int running)
+	       unsigned long load, int running)
 {
 	u32 contrib = (u32)delta; /* p == 0 -> delta < 1024 */
 	u64 periods;
@@ -119,8 +119,6 @@ accumulate_sum(u64 delta, struct sched_avg *sa,
 	 */
 	if (periods) {
 		sa->load_sum = decay_load(sa->load_sum, periods);
-		sa->runnable_load_sum =
-			decay_load(sa->runnable_load_sum, periods);
 		sa->util_sum = decay_load((u64)(sa->util_sum), periods);
 
 		/*
@@ -134,8 +132,6 @@ accumulate_sum(u64 delta, struct sched_avg *sa,
 
 	if (load)
 		sa->load_sum += load * contrib;
-	if (runnable)
-		sa->runnable_load_sum += runnable * contrib;
 	if (running)
 		sa->util_sum += contrib << SCHED_CAPACITY_SHIFT;
 
@@ -172,7 +168,7 @@ accumulate_sum(u64 delta, struct sched_avg *sa,
  */
 static __always_inline int
 ___update_load_sum(u64 now, struct sched_avg *sa,
-		  unsigned long load, unsigned long runnable, int running)
+		  unsigned long load, int running)
 {
 	u64 delta;
 
@@ -206,7 +202,7 @@ ___update_load_sum(u64 now, struct sched_avg *sa,
 	 * update_blocked_averages()
 	 */
 	if (!load)
-		runnable = running = 0;
+		running = 0;
 
 	/*
 	 * Now we know we crossed measurement unit boundaries. The *_avg
@@ -215,14 +211,14 @@ ___update_load_sum(u64 now, struct sched_avg *sa,
 	 * Step 1: accumulate *_sum since last_update_time. If we haven't
 	 * crossed period boundaries, finish.
 	 */
-	if (!accumulate_sum(delta, sa, load, runnable, running))
+	if (!accumulate_sum(delta, sa, load, running))
 		return 0;
 
 	return 1;
 }
 
 static __always_inline void
-___update_load_avg(struct sched_avg *sa, unsigned long load, unsigned long runnable)
+___update_load_avg(struct sched_avg *sa, unsigned long load)
 {
 	u32 divider = LOAD_AVG_MAX - 1024 + sa->period_contrib;
 
@@ -230,7 +226,6 @@ ___update_load_avg(struct sched_avg *sa, unsigned long load, unsigned long runna
 	 * Step 2: update *_avg.
 	 */
 	sa->load_avg = div_u64(load * sa->load_sum, divider);
-	sa->runnable_load_avg =	div_u64(runnable * sa->runnable_load_sum, divider);
 	WRITE_ONCE(sa->util_avg, sa->util_sum / divider);
 }
 
@@ -263,8 +258,8 @@ ___update_load_avg(struct sched_avg *sa, unsigned long load, unsigned long runna
 
 int __update_load_avg_blocked_se(u64 now, struct sched_entity *se)
 {
-	if (___update_load_sum(now, &se->avg, 0, 0, 0)) {
-		___update_load_avg(&se->avg, se_weight(se), se_runnable(se));
+	if (___update_load_sum(now, &se->avg, 0, 0)) {
+		___update_load_avg(&se->avg, se_weight(se));
 		return 1;
 	}
 
@@ -273,10 +268,10 @@ int __update_load_avg_blocked_se(u64 now, struct sched_entity *se)
 
 int __update_load_avg_se(u64 now, struct cfs_rq *cfs_rq, struct sched_entity *se)
 {
-	if (___update_load_sum(now, &se->avg, !!se->on_rq, !!se->on_rq,
+	if (___update_load_sum(now, &se->avg, !!se->on_rq,
 				cfs_rq->curr == se)) {
 
-		___update_load_avg(&se->avg, se_weight(se), se_runnable(se));
+		___update_load_avg(&se->avg, se_weight(se));
 		cfs_se_util_change(&se->avg);
 		return 1;
 	}
@@ -288,10 +283,9 @@ int __update_load_avg_cfs_rq(u64 now, struct cfs_rq *cfs_rq)
 {
 	if (___update_load_sum(now, &cfs_rq->avg,
 				scale_load_down(cfs_rq->load.weight),
-				scale_load_down(cfs_rq->runnable_weight),
 				cfs_rq->curr != NULL)) {
 
-		___update_load_avg(&cfs_rq->avg, 1, 1);
+		___update_load_avg(&cfs_rq->avg, 1);
 		return 1;
 	}
 
@@ -303,20 +297,18 @@ int __update_load_avg_cfs_rq(u64 now, struct cfs_rq *cfs_rq)
  *
  *   util_sum = \Sum se->avg.util_sum but se->avg.util_sum is not tracked
  *   util_sum = cpu_scale * load_sum
- *   runnable_load_sum = load_sum
  *
- *   load_avg and runnable_load_avg are not supported and meaningless.
+ *   load_avg is not supported and meaningless.
  *
  */
 
 int update_rt_rq_load_avg(u64 now, struct rq *rq, int running)
 {
 	if (___update_load_sum(now, &rq->avg_rt,
-				running,
 				running,
 				running)) {
 
-		___update_load_avg(&rq->avg_rt, 1, 1);
+		___update_load_avg(&rq->avg_rt, 1);
 		return 1;
 	}
 
@@ -328,18 +320,16 @@ int update_rt_rq_load_avg(u64 now, struct rq *rq, int running)
  *
  *   util_sum = \Sum se->avg.util_sum but se->avg.util_sum is not tracked
  *   util_sum = cpu_scale * load_sum
- *   runnable_load_sum = load_sum
  *
  */
 
 int update_dl_rq_load_avg(u64 now, struct rq *rq, int running)
 {
 	if (___update_load_sum(now, &rq->avg_dl,
-				running,
 				running,
 				running)) {
 
-		___update_load_avg(&rq->avg_dl, 1, 1);
+		___update_load_avg(&rq->avg_dl, 1);
 		return 1;
 	}
 
@@ -352,7 +342,6 @@ int update_dl_rq_load_avg(u64 now, struct rq *rq, int running)
  *
  *   util_sum = \Sum se->avg.util_sum but se->avg.util_sum is not tracked
  *   util_sum = cpu_scale * load_sum
- *   runnable_load_sum = load_sum
  *
  */
 
@@ -379,17 +368,11 @@ int update_irq_load_avg(struct rq *rq, u64 running)
 	 * We can safely remove running from rq->clock because
 	 * rq->clock += delta with delta >= running
 	 */
-	ret = ___update_load_sum(rq->clock - running, &rq->avg_irq,
-				0,
-				0,
-				0);
-	ret += ___update_load_sum(rq->clock, &rq->avg_irq,
-				1,
-				1,
-				1);
+	ret = ___update_load_sum(rq->clock - running, &rq->avg_irq, 0, 0);
+	ret += ___update_load_sum(rq->clock, &rq->avg_irq, 1, 1);
 
 	if (ret)
-		___update_load_avg(&rq->avg_irq, 1, 1);
+		___update_load_avg(&rq->avg_irq, 1);
 
 	return ret;
 }
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index b52ed1ada0be..5be14cee61f9 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -487,7 +487,6 @@ struct cfs_bandwidth { };
 /* CFS-related fields in a runqueue */
 struct cfs_rq {
 	struct load_weight	load;
-	unsigned long		runnable_weight;
 	unsigned int		nr_running;
 	unsigned int		h_nr_running;
 
@@ -700,11 +699,6 @@ static inline long se_weight(struct sched_entity *se)
 	return scale_load_down(se->load.weight);
 }
 
-static inline long se_runnable(struct sched_entity *se)
-{
-	return scale_load_down(se->runnable_weight);
-}
-
 static inline bool sched_asym_prefer(int a, int b)
 {
 	return arch_asym_cpu_priority(a) > arch_asym_cpu_priority(b);
-- 
2.20.1

[PATCH 04/10] sched,fair: move runnable_load_avg to cfs_rq

[Rik van Riel]

Since only the root cfs_rq runnable_load_avg field is used any more,
we can move the field from struct sched_avg, which every sched_entity
has one of, directly into the struct cfs_rq, of which we have way fewer.

No functional changes.

Suggested-by: Dietmar Eggemann <dietmar.eggemann@arm.com>
Signed-off-by: Rik van Riel <riel@surriel.com>
---
 include/linux/sched.h | 1 -
 kernel/sched/debug.c  | 3 +--
 kernel/sched/fair.c   | 8 ++++----
 kernel/sched/sched.h  | 1 +
 4 files changed, 6 insertions(+), 7 deletions(-)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index f5bb6948e40c..84a6cc6f5c47 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -394,7 +394,6 @@ struct sched_avg {
 	u32				util_sum;
 	u32				period_contrib;
 	unsigned long			load_avg;
-	unsigned long			runnable_load_avg;
 	unsigned long			util_avg;
 	struct util_est			util_est;
 } ____cacheline_aligned;
diff --git a/kernel/sched/debug.c b/kernel/sched/debug.c
index cefc1b171c0b..6e7c8ff210a8 100644
--- a/kernel/sched/debug.c
+++ b/kernel/sched/debug.c
@@ -539,7 +539,7 @@ void print_cfs_rq(struct seq_file *m, int cpu, struct cfs_rq *cfs_rq)
 	SEQ_printf(m, "  .%-30s: %lu\n", "load_avg",
 			cfs_rq->avg.load_avg);
 	SEQ_printf(m, "  .%-30s: %lu\n", "runnable_load_avg",
-			cfs_rq->avg.runnable_load_avg);
+			cfs_rq->runnable_load_avg);
 	SEQ_printf(m, "  .%-30s: %lu\n", "util_avg",
 			cfs_rq->avg.util_avg);
 	SEQ_printf(m, "  .%-30s: %u\n", "util_est_enqueued",
@@ -960,7 +960,6 @@ void proc_sched_show_task(struct task_struct *p, struct pid_namespace *ns,
 	P(se.avg.load_sum);
 	P(se.avg.util_sum);
 	P(se.avg.load_avg);
-	P(se.avg.runnable_load_avg);
 	P(se.avg.util_avg);
 	P(se.enqueued_h_load);
 	P(se.avg.last_update_time);
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 860708b687a7..63cb40253b26 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -2768,7 +2768,7 @@ enqueue_runnable_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *se)
 		struct cfs_rq *root_cfs_rq = &cfs_rq->rq->cfs;
 		se->enqueued_h_load = task_se_h_load(se);
 
-		root_cfs_rq->avg.runnable_load_avg += se->enqueued_h_load;
+		root_cfs_rq->runnable_load_avg += se->enqueued_h_load;
 	}
 }
 
@@ -2777,7 +2777,7 @@ dequeue_runnable_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *se)
 {
 	if (entity_is_task(se)) {
 		struct cfs_rq *root_cfs_rq = &cfs_rq->rq->cfs;
-		sub_positive(&root_cfs_rq->avg.runnable_load_avg,
+		sub_positive(&root_cfs_rq->runnable_load_avg,
 					se->enqueued_h_load);
 	}
 }
@@ -2795,7 +2795,7 @@ update_runnable_load_avg(struct sched_entity *se)
 
 	new_h_load = task_se_h_load(se);
 	delta = new_h_load - se->enqueued_h_load;
-	root_cfs_rq->avg.runnable_load_avg += delta;
+	root_cfs_rq->runnable_load_avg += delta;
 	se->enqueued_h_load = new_h_load;
 }
 
@@ -3559,7 +3559,7 @@ static void remove_entity_load_avg(struct sched_entity *se)
 
 static inline unsigned long cfs_rq_runnable_load_avg(struct cfs_rq *cfs_rq)
 {
-	return cfs_rq->avg.runnable_load_avg;
+	return cfs_rq->runnable_load_avg;
 }
 
 static inline unsigned long cfs_rq_load_avg(struct cfs_rq *cfs_rq)
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 5be14cee61f9..32978a8de8ce 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -516,6 +516,7 @@ struct cfs_rq {
 	 * CFS load tracking
 	 */
 	struct sched_avg	avg;
+	unsigned long		runnable_load_avg;
 #ifndef CONFIG_64BIT
 	u64			load_last_update_time_copy;
 #endif
-- 
2.20.1

[PATCH 05/10] sched,fair: remove cfs rqs from leaf_cfs_rq_list bottom up

[Rik van Riel]

Reducing the overhead of the CPU controller is achieved by not walking
all the sched_entities every time a task is enqueued or dequeued.

One of the things being checked every single time is whether the cfs_rq
is on the rq->leaf_cfs_rq_list.

By only removing a cfs_rq from the list once it no longer has children
on the list, we can avoid walking the sched_entity hierarchy if the bottom
cfs_rq is on the list, once the runqueues have been flattened.

Signed-off-by: Rik van Riel <riel@surriel.com>
---
 kernel/sched/fair.c  | 17 +++++++++++++++++
 kernel/sched/sched.h |  1 +
 2 files changed, 18 insertions(+)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 63cb40253b26..e41feacc45d9 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -286,6 +286,13 @@ static inline bool list_add_leaf_cfs_rq(struct cfs_rq *cfs_rq)
 
 	cfs_rq->on_list = 1;
 
+	/*
+	 * If the tmp_alone_branch cursor was moved, it means a child cfs_rq
+	 * is already on the list ahead of us.
+	 */
+	if (rq->tmp_alone_branch != &rq->leaf_cfs_rq_list)
+		cfs_rq->children_on_list++;
+
 	/*
 	 * Ensure we either appear before our parent (if already
 	 * enqueued) or force our parent to appear after us when it is
@@ -311,6 +318,7 @@ static inline bool list_add_leaf_cfs_rq(struct cfs_rq *cfs_rq)
 		 * list.
 		 */
 		rq->tmp_alone_branch = &rq->leaf_cfs_rq_list;
+		cfs_rq->tg->parent->cfs_rq[cpu]->children_on_list++;
 		return true;
 	}
 
@@ -359,6 +367,11 @@ static inline void list_del_leaf_cfs_rq(struct cfs_rq *cfs_rq)
 		if (rq->tmp_alone_branch == &cfs_rq->leaf_cfs_rq_list)
 			rq->tmp_alone_branch = cfs_rq->leaf_cfs_rq_list.prev;
 
+		if (cfs_rq->tg->parent) {
+			int cpu = cpu_of(rq);
+			cfs_rq->tg->parent->cfs_rq[cpu]->children_on_list--;
+		}
+
 		list_del_rcu(&cfs_rq->leaf_cfs_rq_list);
 		cfs_rq->on_list = 0;
 	}
@@ -7687,6 +7700,10 @@ static inline bool cfs_rq_is_decayed(struct cfs_rq *cfs_rq)
 	if (cfs_rq->avg.util_sum)
 		return false;
 
+	/* Remove decayed parents once their decayed children are gone. */
+	if (cfs_rq->children_on_list)
+		return false;
+
 	return true;
 }
 
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 32978a8de8ce..4f8acbab0fb2 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -557,6 +557,7 @@ struct cfs_rq {
 	 * This list is used during load balance.
 	 */
 	int			on_list;
+	int			children_on_list;
 	struct list_head	leaf_cfs_rq_list;
 	struct task_group	*tg;	/* group that "owns" this runqueue */
 
-- 
2.20.1

[PATCH 06/10] sched,cfs: use explicit cfs_rq of parent se helper

[Rik van Riel]

Use an explicit "cfs_rq of parent sched_entity" helper in a few
strategic places, where cfs_rq_of(se) may no longer point at the
right runqueue once we flatten the hierarchical cgroup runqueues.

No functional change.

Signed-off-by: Rik van Riel <riel@surriel.com>
---
 kernel/sched/fair.c | 17 +++++++++++++----
 1 file changed, 13 insertions(+), 4 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index e41feacc45d9..d48bff5118fc 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -276,6 +276,15 @@ static inline struct cfs_rq *group_cfs_rq(struct sched_entity *grp)
 	return grp->my_q;
 }
 
+/* runqueue owned by the parent entity; the root cfs_rq for a top level se */
+static inline struct cfs_rq *group_cfs_rq_of_parent(struct sched_entity *se)
+{
+	if (se->parent)
+		return group_cfs_rq(se->parent);
+
+	return cfs_rq_of(se);
+}
+
 static inline bool list_add_leaf_cfs_rq(struct cfs_rq *cfs_rq)
 {
 	struct rq *rq = rq_of(cfs_rq);
@@ -3297,7 +3306,7 @@ static inline int propagate_entity_load_avg(struct sched_entity *se)
 
 	gcfs_rq->propagate = 0;
 
-	cfs_rq = cfs_rq_of(se);
+	cfs_rq = group_cfs_rq_of_parent(se);
 
 	add_tg_cfs_propagate(cfs_rq, gcfs_rq->prop_runnable_sum);
 
@@ -7778,7 +7787,7 @@ static void update_cfs_rq_h_load(struct cfs_rq *cfs_rq)
 
 	WRITE_ONCE(cfs_rq->h_load_next, NULL);
 	for_each_sched_entity(se) {
-		cfs_rq = cfs_rq_of(se);
+		cfs_rq = group_cfs_rq_of_parent(se);
 		WRITE_ONCE(cfs_rq->h_load_next, se);
 		if (cfs_rq->last_h_load_update == now)
 			break;
@@ -7801,7 +7810,7 @@ static void update_cfs_rq_h_load(struct cfs_rq *cfs_rq)
 
 static unsigned long task_se_h_load(struct sched_entity *se)
 {
-	struct cfs_rq *cfs_rq = cfs_rq_of(se);
+	struct cfs_rq *cfs_rq = group_cfs_rq_of_parent(se);
 
 	update_cfs_rq_h_load(cfs_rq);
 	return div64_ul(se->avg.load_avg * cfs_rq->h_load,
@@ -10148,7 +10157,7 @@ static void task_tick_fair(struct rq *rq, struct task_struct *curr, int queued)
 	struct sched_entity *se = &curr->se;
 
 	for_each_sched_entity(se) {
-		cfs_rq = cfs_rq_of(se);
+		cfs_rq = group_cfs_rq_of_parent(se);
 		entity_tick(cfs_rq, se, queued);
 	}
 
-- 
2.20.1

[PATCH 07/10] sched,cfs: fix zero length timeslice calculation

[Rik van Riel]

The way the time slice length is currently calculated, not only do high
priority tasks get longer time slices than low priority tasks, but due
to fixed point math, low priority tasks could end up with a zero length
time slice. This can lead to cache thrashing and other inefficiencies.

Simplify the logic a little bit, and cap the minimum time slice length
to sysctl_sched_min_granularity.

Tasks that end up getting a time slice length too long for their relative
priority will simply end up having their vruntime advanced much faster than
other tasks, resulting in them receiving time slices less frequently.

Signed-off-by: Rik van Riel <riel@surriel.com>
---
 kernel/sched/fair.c | 25 ++++++++-----------------
 1 file changed, 8 insertions(+), 17 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index d48bff5118fc..8da2823401ca 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -671,22 +671,6 @@ static inline u64 calc_delta_fair(u64 delta, struct sched_entity *se)
 	return delta;
 }
 
-/*
- * The idea is to set a period in which each task runs once.
- *
- * When there are too many tasks (sched_nr_latency) we have to stretch
- * this period because otherwise the slices get too small.
- *
- * p = (nr <= nl) ? l : l*nr/nl
- */
-static u64 __sched_period(unsigned long nr_running)
-{
-	if (unlikely(nr_running > sched_nr_latency))
-		return nr_running * sysctl_sched_min_granularity;
-	else
-		return sysctl_sched_latency;
-}
-
 /*
  * We calculate the wall-time slice from the period by taking a part
  * proportional to the weight.
@@ -695,7 +679,7 @@ static u64 __sched_period(unsigned long nr_running)
  */
 static u64 sched_slice(struct cfs_rq *cfs_rq, struct sched_entity *se)
 {
-	u64 slice = __sched_period(cfs_rq->nr_running + !se->on_rq);
+	u64 slice = sysctl_sched_latency;
 
 	for_each_sched_entity(se) {
 		struct load_weight *load;
@@ -712,6 +696,13 @@ static u64 sched_slice(struct cfs_rq *cfs_rq, struct sched_entity *se)
 		}
 		slice = __calc_delta(slice, se->load.weight, load);
 	}
+
+	/*
+	 * To avoid cache thrashing, run at least sysctl_sched_min_granularity.
+	 * The vruntime of a low priority task advances faster; those tasks
+	 * will simply get time slices less frequently.
+	 */
+	slice = max_t(u64, slice, sysctl_sched_min_granularity);
 	return slice;
 }
 
-- 
2.20.1

[PATCH 08/10] sched,fair: refactor enqueue/dequeue_entity

[Rik van Riel]

Refactor enqueue_entity, dequeue_entity, and update_load_avg, in order
to split out the things we still want to happen at every level in the
cgroup hierarchy with a flat runqueue from the things we only need to
happen once.

No functional changes.

Signed-off-by: Rik van Riel <riel@surriel.com>
---
 kernel/sched/fair.c | 64 +++++++++++++++++++++++++++++----------------
 1 file changed, 42 insertions(+), 22 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 8da2823401ca..a751e7a9b228 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -3480,7 +3480,7 @@ static void detach_entity_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *s
 #define DO_ATTACH	0x4
 
 /* Update task and its cfs_rq load average */
-static inline void update_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *se, int flags)
+static inline bool update_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *se, int flags)
 {
 	u64 now = cfs_rq_clock_pelt(cfs_rq);
 	int decayed;
@@ -3509,6 +3509,8 @@ static inline void update_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *s
 
 	} else if (decayed && (flags & UPDATE_TG))
 		update_tg_load_avg(cfs_rq, 0);
+
+	return decayed;
 }
 
 #ifndef CONFIG_64BIT
@@ -3725,9 +3727,10 @@ static inline void update_misfit_status(struct task_struct *p, struct rq *rq)
 #define SKIP_AGE_LOAD	0x0
 #define DO_ATTACH	0x0
 
-static inline void update_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *se, int not_used1)
+static inline bool update_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *se, int not_used1)
 {
 	cfs_rq_util_change(cfs_rq, 0);
+	return false;
 }
 
 static inline void remove_entity_load_avg(struct sched_entity *se) {}
@@ -3850,6 +3853,24 @@ static inline void check_schedstat_required(void)
  * CPU and an up-to-date min_vruntime on the destination CPU.
  */
 
+static bool
+enqueue_entity_groups(struct cfs_rq *cfs_rq, struct sched_entity *se, int flags)
+{
+	/*
+	 * When enqueuing a sched_entity, we must:
+	 *   - Update loads to have both entity and cfs_rq synced with now.
+	 *   - Add its load to cfs_rq->runnable_avg
+	 *   - For group_entity, update its weight to reflect the new share of
+	 *     its group cfs_rq
+	 *   - Add its new weight to cfs_rq->load.weight
+	 */
+	if (!update_load_avg(cfs_rq, se, UPDATE_TG | DO_ATTACH))
+		return false;
+
+	update_cfs_group(se);
+	return true;
+}
+
 static void
 enqueue_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int flags)
 {
@@ -3874,16 +3895,6 @@ enqueue_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int flags)
 	if (renorm && !curr)
 		se->vruntime += cfs_rq->min_vruntime;
 
-	/*
-	 * When enqueuing a sched_entity, we must:
-	 *   - Update loads to have both entity and cfs_rq synced with now.
-	 *   - Add its load to cfs_rq->runnable_avg
-	 *   - For group_entity, update its weight to reflect the new share of
-	 *     its group cfs_rq
-	 *   - Add its new weight to cfs_rq->load.weight
-	 */
-	update_load_avg(cfs_rq, se, UPDATE_TG | DO_ATTACH);
-	update_cfs_group(se);
 	enqueue_runnable_load_avg(cfs_rq, se);
 	account_entity_enqueue(cfs_rq, se);
 
@@ -3950,14 +3961,9 @@ static void clear_buddies(struct cfs_rq *cfs_rq, struct sched_entity *se)
 
 static __always_inline void return_cfs_rq_runtime(struct cfs_rq *cfs_rq);
 
-static void
-dequeue_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int flags)
+static bool
+dequeue_entity_groups(struct cfs_rq *cfs_rq, struct sched_entity *se, int flags)
 {
-	/*
-	 * Update run-time statistics of the 'current'.
-	 */
-	update_curr(cfs_rq);
-
 	/*
 	 * When dequeuing a sched_entity, we must:
 	 *   - Update loads to have both entity and cfs_rq synced with now.
@@ -3966,7 +3972,21 @@ dequeue_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int flags)
 	 *   - For group entity, update its weight to reflect the new share
 	 *     of its group cfs_rq.
 	 */
-	update_load_avg(cfs_rq, se, UPDATE_TG);
+	if (!update_load_avg(cfs_rq, se, UPDATE_TG))
+		return false;
+	update_cfs_group(se);
+
+	return true;
+}
+
+static void
+dequeue_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int flags)
+{
+	/*
+	 * Update run-time statistics of the 'current'.
+	 */
+	update_curr(cfs_rq);
+
 	dequeue_runnable_load_avg(cfs_rq, se);
 
 	update_stats_dequeue(cfs_rq, se, flags);
@@ -3990,8 +4010,6 @@ dequeue_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int flags)
 	/* return excess runtime on last dequeue */
 	return_cfs_rq_runtime(cfs_rq);
 
-	update_cfs_group(se);
-
 	/*
 	 * Now advance min_vruntime if @se was the entity holding it back,
 	 * except when: DEQUEUE_SAVE && !DEQUEUE_MOVE, in this case we'll be
@@ -5156,6 +5174,7 @@ enqueue_task_fair(struct rq *rq, struct task_struct *p, int flags)
 		if (se->on_rq)
 			break;
 		cfs_rq = cfs_rq_of(se);
+		enqueue_entity_groups(cfs_rq, se, flags);
 		enqueue_entity(cfs_rq, se, flags);
 
 		/*
@@ -5238,6 +5257,7 @@ static void dequeue_task_fair(struct rq *rq, struct task_struct *p, int flags)
 
 	for_each_sched_entity(se) {
 		cfs_rq = cfs_rq_of(se);
+		dequeue_entity_groups(cfs_rq, se, flags);
 		dequeue_entity(cfs_rq, se, flags);
 
 		/*
-- 
2.20.1

[PATCH 09/10] sched,fair: add helper functions for flattened runqueue

[Rik van Riel]

Add helper functions to make the flattened runqueue patch a little smaller.

The task_se_h_weight function is similar to task_se_h_load, but scales the
task weight by the group weight, without taking the task's duty cycle into
account.

The task_se_in_cgroup helper is functionally identical to parent_entity,
but directly calling a function with that name obscures what the other
code is trying to use it for, and would make the code harder to understand.

Signed-off-by: Rik van Riel <riel@surriel.com>
---
 kernel/sched/fair.c | 26 ++++++++++++++++++++++++++
 1 file changed, 26 insertions(+)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index a751e7a9b228..6fea8849cc12 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -243,6 +243,7 @@ static u64 __calc_delta(u64 delta_exec, unsigned long weight, struct load_weight
 
 const struct sched_class fair_sched_class;
 static unsigned long task_se_h_load(struct sched_entity *se);
+static unsigned long task_se_h_weight(struct sched_entity *se);
 
 /**************************************************************
  * CFS operations on generic schedulable entities:
@@ -411,6 +412,12 @@ static inline struct sched_entity *parent_entity(struct sched_entity *se)
 	return se->parent;
 }
 
+/* Is this (task) sched_entity in a non-root cgroup? */
+static inline bool task_se_in_cgroup(struct sched_entity *se)
+{
+	return parent_entity(se);
+}
+
 static void
 find_matching_se(struct sched_entity **se, struct sched_entity **pse)
 {
@@ -7819,6 +7826,20 @@ static void update_cfs_rq_h_load(struct cfs_rq *cfs_rq)
 	}
 }
 
+static unsigned long task_se_h_weight(struct sched_entity *se)
+{
+	struct cfs_rq *cfs_rq;
+
+	if (!task_se_in_cgroup(se))
+		return se->load.weight;
+
+	cfs_rq = group_cfs_rq_of_parent(se);
+	update_cfs_rq_h_load(cfs_rq);
+
+	/* Reduce the load.weight by the h_load of the group the task is in. */
+	return (cfs_rq->h_load * se->load.weight) >> SCHED_FIXEDPOINT_SHIFT;
+}
+
 static unsigned long task_se_h_load(struct sched_entity *se)
 {
 	struct cfs_rq *cfs_rq = group_cfs_rq_of_parent(se);
@@ -7855,6 +7876,11 @@ static unsigned long task_se_h_load(struct sched_entity *se)
 {
 	return se->avg.load_avg;
 }
+
+static unsigned long task_se_h_weight(struct sched_entity *se)
+{
+	return se->load.weight;
+}
 #endif
 
 /********** Helpers for find_busiest_group ************************/
-- 
2.20.1

[PATCH 10/10] sched,fair: flatten hierarchical runqueues

[Rik van Riel]

Flatten the hierarchical runqueues into just the per CPU rq.cfs runqueue.

Iteration of the sched_entity hierarchy is rate limited to once per jiffy
per sched_entity, which is a smaller change than it seems, because load
average adjustments were already rate limited to once per jiffy before this
patch series.

This patch breaks CONFIG_CFS_BANDWIDTH. The plan for that is to park tasks
from throttled cgroups onto their cgroup runqueues, and slowly (using the
GENTLE_FAIR_SLEEPERS) wake them back up, in vruntime order, once the cgroup
gets unthrottled, to prevent thundering herd issues.

Signed-off-by: Rik van Riel <riel@surriel.com>
---
 include/linux/sched.h |   2 +
 kernel/sched/fair.c   | 452 +++++++++++++++---------------------------
 kernel/sched/pelt.c   |   6 +-
 kernel/sched/pelt.h   |   2 +-
 kernel/sched/sched.h  |   2 +-
 5 files changed, 171 insertions(+), 293 deletions(-)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 84a6cc6f5c47..901c710363e7 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -453,6 +453,8 @@ struct sched_entity {
 #ifdef CONFIG_FAIR_GROUP_SCHED
 	int				depth;
 	unsigned long			enqueued_h_load;
+	unsigned long			enqueued_h_weight;
+	struct load_weight		h_load;
 	struct sched_entity		*parent;
 	/* rq on which this entity is (to be) queued: */
 	struct cfs_rq			*cfs_rq;
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 6fea8849cc12..c31d3da081fb 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -450,6 +450,19 @@ find_matching_se(struct sched_entity **se, struct sched_entity **pse)
 	}
 }
 
+/* Add the cgroup cfs_rqs to the list, for update_blocked_averages */
+static void enqueue_entity_cfs_rqs(struct sched_entity *se)
+{
+	SCHED_WARN_ON(!entity_is_task(se));
+
+	for_each_sched_entity(se) {
+		struct cfs_rq *cfs_rq = group_cfs_rq_of_parent(se);
+
+		if (list_add_leaf_cfs_rq(cfs_rq))
+			break;
+	}
+}
+
 #else	/* !CONFIG_FAIR_GROUP_SCHED */
 
 static inline struct task_struct *task_of(struct sched_entity *se)
@@ -672,8 +685,14 @@ int sched_proc_update_handler(struct ctl_table *table, int write,
  */
 static inline u64 calc_delta_fair(u64 delta, struct sched_entity *se)
 {
-	if (unlikely(se->load.weight != NICE_0_LOAD))
+	if (task_se_in_cgroup(se)) {
+		unsigned long h_weight = task_se_h_weight(se);
+		if (h_weight != se->h_load.weight)
+			update_load_set(&se->h_load, h_weight);
+		delta = __calc_delta(delta, NICE_0_LOAD, &se->h_load);
+	} else if (unlikely(se->load.weight != NICE_0_LOAD)) {
 		delta = __calc_delta(delta, NICE_0_LOAD, &se->load);
+	}
 
 	return delta;
 }
@@ -687,22 +706,16 @@ static inline u64 calc_delta_fair(u64 delta, struct sched_entity *se)
 static u64 sched_slice(struct cfs_rq *cfs_rq, struct sched_entity *se)
 {
 	u64 slice = sysctl_sched_latency;
+	struct load_weight *load = &cfs_rq->load;
+	struct load_weight lw;
 
-	for_each_sched_entity(se) {
-		struct load_weight *load;
-		struct load_weight lw;
-
-		cfs_rq = cfs_rq_of(se);
-		load = &cfs_rq->load;
+	if (unlikely(!se->on_rq)) {
+		lw = cfs_rq->load;
 
-		if (unlikely(!se->on_rq)) {
-			lw = cfs_rq->load;
-
-			update_load_add(&lw, se->load.weight);
-			load = &lw;
-		}
-		slice = __calc_delta(slice, se->load.weight, load);
+		update_load_add(&lw, task_se_h_weight(se));
+		load = &lw;
 	}
+	slice = __calc_delta(slice, task_se_h_weight(se), load);
 
 	/*
 	 * To avoid cache thrashing, run at least sysctl_sched_min_granularity.
@@ -2703,16 +2716,28 @@ static inline void update_scan_period(struct task_struct *p, int new_cpu)
 static void
 account_entity_enqueue(struct cfs_rq *cfs_rq, struct sched_entity *se)
 {
-	update_load_add(&cfs_rq->load, se->load.weight);
-	if (!parent_entity(se))
+	struct rq *rq;
+
+	if (task_se_in_cgroup(se)) {
+		struct cfs_rq *cgroup_rq = group_cfs_rq_of_parent(se);
+		unsigned long h_weight;
+
+		update_load_add(&cgroup_rq->load, se->load.weight);
+		cgroup_rq->nr_running++;
+
+		/* Add the hierarchical weight to the CPU rq */
+		h_weight = task_se_h_weight(se);
+		se->enqueued_h_weight = h_weight;
+		update_load_add(&rq_of(cfs_rq)->load, h_weight);
+	} else {
+		update_load_add(&cfs_rq->load, se->load.weight);
 		update_load_add(&rq_of(cfs_rq)->load, se->load.weight);
+	}
 #ifdef CONFIG_SMP
-	if (entity_is_task(se)) {
-		struct rq *rq = rq_of(cfs_rq);
+	rq = rq_of(cfs_rq);
 
-		account_numa_enqueue(rq, task_of(se));
-		list_add(&se->group_node, &rq->cfs_tasks);
-	}
+	account_numa_enqueue(rq, task_of(se));
+	list_add(&se->group_node, &rq->cfs_tasks);
 #endif
 	cfs_rq->nr_running++;
 }
@@ -2720,14 +2745,20 @@ account_entity_enqueue(struct cfs_rq *cfs_rq, struct sched_entity *se)
 static void
 account_entity_dequeue(struct cfs_rq *cfs_rq, struct sched_entity *se)
 {
-	update_load_sub(&cfs_rq->load, se->load.weight);
-	if (!parent_entity(se))
+	if (task_se_in_cgroup(se)) {
+		struct cfs_rq *cgroup_rq = group_cfs_rq_of_parent(se);
+
+		update_load_sub(&cgroup_rq->load, se->load.weight);
+		cgroup_rq->nr_running--;
+
+		update_load_sub(&rq_of(cfs_rq)->load, se->enqueued_h_weight);
+	} else {
+		update_load_sub(&cfs_rq->load, se->load.weight);
 		update_load_sub(&rq_of(cfs_rq)->load, se->load.weight);
-#ifdef CONFIG_SMP
-	if (entity_is_task(se)) {
-		account_numa_dequeue(rq_of(cfs_rq), task_of(se));
-		list_del_init(&se->group_node);
 	}
+#ifdef CONFIG_SMP
+	account_numa_dequeue(rq_of(cfs_rq), task_of(se));
+	list_del_init(&se->group_node);
 #endif
 	cfs_rq->nr_running--;
 }
@@ -2822,6 +2853,9 @@ update_runnable_load_avg(struct sched_entity *se)
 static inline void
 enqueue_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *se)
 {
+	if (task_se_in_cgroup(se))
+		cfs_rq = group_cfs_rq_of_parent(se);
+
 	cfs_rq->avg.load_avg += se->avg.load_avg;
 	cfs_rq->avg.load_sum += se_weight(se) * se->avg.load_sum;
 }
@@ -2829,6 +2863,9 @@ enqueue_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *se)
 static inline void
 dequeue_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *se)
 {
+	if (task_se_in_cgroup(se))
+		cfs_rq = group_cfs_rq_of_parent(se);
+
 	sub_positive(&cfs_rq->avg.load_avg, se->avg.load_avg);
 	sub_positive(&cfs_rq->avg.load_sum, se_weight(se) * se->avg.load_sum);
 }
@@ -3455,7 +3492,9 @@ static void attach_entity_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *s
 	cfs_rq->avg.util_avg += se->avg.util_avg;
 	cfs_rq->avg.util_sum += se->avg.util_sum;
 
-	add_tg_cfs_propagate(cfs_rq, se->avg.load_sum);
+	if (task_se_in_cgroup(se))
+		add_tg_cfs_propagate(group_cfs_rq_of_parent(se),
+						se->avg.load_sum);
 
 	cfs_rq_util_change(cfs_rq, flags);
 }
@@ -3474,7 +3513,9 @@ static void detach_entity_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *s
 	sub_positive(&cfs_rq->avg.util_avg, se->avg.util_avg);
 	sub_positive(&cfs_rq->avg.util_sum, se->avg.util_sum);
 
-	add_tg_cfs_propagate(cfs_rq, -se->avg.load_sum);
+	if (task_se_in_cgroup(se))
+		add_tg_cfs_propagate(group_cfs_rq_of_parent(se),
+						-se->avg.load_sum);
 
 	cfs_rq_util_change(cfs_rq, 0);
 }
@@ -3485,11 +3526,13 @@ static void detach_entity_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *s
 #define UPDATE_TG	0x1
 #define SKIP_AGE_LOAD	0x2
 #define DO_ATTACH	0x4
+#define SE_IS_CURRENT	0x8
 
 /* Update task and its cfs_rq load average */
 static inline bool update_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *se, int flags)
 {
 	u64 now = cfs_rq_clock_pelt(cfs_rq);
+	bool curr = flags & SE_IS_CURRENT;
 	int decayed;
 
 	/*
@@ -3497,7 +3540,7 @@ static inline bool update_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *s
 	 * track group sched_entity load average for task_se_h_load calc in migration
 	 */
 	if (se->avg.last_update_time && !(flags & SKIP_AGE_LOAD))
-		__update_load_avg_se(now, cfs_rq, se);
+		__update_load_avg_se(now, cfs_rq, se, curr, curr);
 
 	decayed  = update_cfs_rq_load_avg(now, cfs_rq);
 	decayed |= propagate_entity_load_avg(se);
@@ -3563,6 +3606,9 @@ static void remove_entity_load_avg(struct sched_entity *se)
 	struct cfs_rq *cfs_rq = cfs_rq_of(se);
 	unsigned long flags;
 
+	if (task_se_in_cgroup(se))
+		cfs_rq = group_cfs_rq_of_parent(se);
+
 	/*
 	 * tasks cannot exit without having gone through wake_up_new_task() ->
 	 * post_init_entity_util_avg() which will have added things to the
@@ -3733,6 +3779,7 @@ static inline void update_misfit_status(struct task_struct *p, struct rq *rq)
 #define UPDATE_TG	0x0
 #define SKIP_AGE_LOAD	0x0
 #define DO_ATTACH	0x0
+#define SE_IS_CURRENT	0x0
 
 static inline bool update_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *se, int not_used1)
 {
@@ -3915,55 +3962,20 @@ enqueue_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int flags)
 		__enqueue_entity(cfs_rq, se);
 	se->on_rq = 1;
 
-	if (cfs_rq->nr_running == 1) {
-		list_add_leaf_cfs_rq(cfs_rq);
-		check_enqueue_throttle(cfs_rq);
-	}
-}
-
-static void __clear_buddies_last(struct sched_entity *se)
-{
-	for_each_sched_entity(se) {
-		struct cfs_rq *cfs_rq = cfs_rq_of(se);
-		if (cfs_rq->last != se)
-			break;
-
-		cfs_rq->last = NULL;
-	}
-}
-
-static void __clear_buddies_next(struct sched_entity *se)
-{
-	for_each_sched_entity(se) {
-		struct cfs_rq *cfs_rq = cfs_rq_of(se);
-		if (cfs_rq->next != se)
-			break;
-
-		cfs_rq->next = NULL;
-	}
-}
-
-static void __clear_buddies_skip(struct sched_entity *se)
-{
-	for_each_sched_entity(se) {
-		struct cfs_rq *cfs_rq = cfs_rq_of(se);
-		if (cfs_rq->skip != se)
-			break;
-
-		cfs_rq->skip = NULL;
-	}
+	if (task_se_in_cgroup(se))
+		enqueue_entity_cfs_rqs(se);
 }
 
 static void clear_buddies(struct cfs_rq *cfs_rq, struct sched_entity *se)
 {
 	if (cfs_rq->last == se)
-		__clear_buddies_last(se);
+		cfs_rq->last = NULL;
 
 	if (cfs_rq->next == se)
-		__clear_buddies_next(se);
+		cfs_rq->next = NULL;
 
 	if (cfs_rq->skip == se)
-		__clear_buddies_skip(se);
+		cfs_rq->skip = NULL;
 }
 
 static __always_inline void return_cfs_rq_runtime(struct cfs_rq *cfs_rq);
@@ -4072,6 +4084,7 @@ set_next_entity(struct cfs_rq *cfs_rq, struct sched_entity *se)
 {
 	/* 'current' is not kept within the tree. */
 	if (se->on_rq) {
+		struct sched_entity *ise = se;
 		/*
 		 * Any task has to be enqueued before it get to execute on
 		 * a CPU. So account for the time it spent waiting on the
@@ -4079,7 +4092,11 @@ set_next_entity(struct cfs_rq *cfs_rq, struct sched_entity *se)
 		 */
 		update_stats_wait_end(cfs_rq, se);
 		__dequeue_entity(cfs_rq, se);
-		update_load_avg(cfs_rq, se, UPDATE_TG);
+		for_each_sched_entity(ise) {
+			struct cfs_rq *group_rq = group_cfs_rq_of_parent(ise);
+			if (!update_load_avg(group_rq, ise, UPDATE_TG))
+				break;
+		}
 	}
 
 	update_stats_curr_start(cfs_rq, se);
@@ -4177,11 +4194,16 @@ static void put_prev_entity(struct cfs_rq *cfs_rq, struct sched_entity *prev)
 	check_spread(cfs_rq, prev);
 
 	if (prev->on_rq) {
+		struct sched_entity *se = prev;
 		update_stats_wait_start(cfs_rq, prev);
 		/* Put 'current' back into the tree. */
 		__enqueue_entity(cfs_rq, prev);
 		/* in !on_rq case, update occurred at dequeue */
-		update_load_avg(cfs_rq, prev, 0);
+		for_each_sched_entity(se) {
+			struct cfs_rq *group_rq = group_cfs_rq_of_parent(se);
+			if (!update_load_avg(group_rq, se, SE_IS_CURRENT))
+				break;
+		}
 	}
 	cfs_rq->curr = NULL;
 }
@@ -4197,7 +4219,7 @@ entity_tick(struct cfs_rq *cfs_rq, struct sched_entity *curr, int queued)
 	/*
 	 * Ensure that runnable average is periodically updated.
 	 */
-	update_load_avg(cfs_rq, curr, UPDATE_TG);
+	update_load_avg(cfs_rq, curr, UPDATE_TG|SE_IS_CURRENT);
 	update_cfs_group(curr);
 
 #ifdef CONFIG_SCHED_HRTICK
@@ -4216,9 +4238,6 @@ entity_tick(struct cfs_rq *cfs_rq, struct sched_entity *curr, int queued)
 			hrtimer_active(&rq_of(cfs_rq)->hrtick_timer))
 		return;
 #endif
-
-	if (cfs_rq->nr_running > 1)
-		check_preempt_tick(cfs_rq, curr);
 }
 
 
@@ -5093,7 +5112,7 @@ static void hrtick_start_fair(struct rq *rq, struct task_struct *p)
 
 	SCHED_WARN_ON(task_rq(p) != rq);
 
-	if (rq->cfs.h_nr_running > 1) {
+	if (rq->cfs.nr_running > 1) {
 		u64 slice = sched_slice(cfs_rq, se);
 		u64 ran = se->sum_exec_runtime - se->prev_sum_exec_runtime;
 		s64 delta = slice - ran;
@@ -5158,7 +5177,7 @@ static inline void update_overutilized_status(struct rq *rq) { }
 static void
 enqueue_task_fair(struct rq *rq, struct task_struct *p, int flags)
 {
-	struct cfs_rq *cfs_rq;
+	struct cfs_rq *cfs_rq = & rq->cfs;
 	struct sched_entity *se = &p->se;
 
 	/*
@@ -5167,7 +5186,7 @@ enqueue_task_fair(struct rq *rq, struct task_struct *p, int flags)
 	 * Let's add the task's estimated utilization to the cfs_rq's
 	 * estimated utilization, before we update schedutil.
 	 */
-	util_est_enqueue(&rq->cfs, p);
+	util_est_enqueue(cfs_rq, p);
 
 	/*
 	 * If in_iowait is set, the code below may not trigger any cpufreq
@@ -5178,37 +5197,13 @@ enqueue_task_fair(struct rq *rq, struct task_struct *p, int flags)
 		cpufreq_update_util(rq, SCHED_CPUFREQ_IOWAIT);
 
 	for_each_sched_entity(se) {
-		if (se->on_rq)
-			break;
-		cfs_rq = cfs_rq_of(se);
-		enqueue_entity_groups(cfs_rq, se, flags);
-		enqueue_entity(cfs_rq, se, flags);
-
-		/*
-		 * end evaluation on encountering a throttled cfs_rq
-		 *
-		 * note: in the case of encountering a throttled cfs_rq we will
-		 * post the final h_nr_running increment below.
-		 */
-		if (cfs_rq_throttled(cfs_rq))
+		struct cfs_rq *group_rq = group_cfs_rq_of_parent(se);
+		if (!enqueue_entity_groups(group_rq, se, flags))
 			break;
-		cfs_rq->h_nr_running++;
-
-		flags = ENQUEUE_WAKEUP;
 	}
 
-	for_each_sched_entity(se) {
-		cfs_rq = cfs_rq_of(se);
-		cfs_rq->h_nr_running++;
-
-		if (cfs_rq_throttled(cfs_rq))
-			break;
-
-		update_load_avg(cfs_rq, se, UPDATE_TG);
-		update_cfs_group(se);
-	}
+	enqueue_entity(cfs_rq, &p->se, flags);
 
-	if (!se) {
 		add_nr_running(rq, 1);
 		/*
 		 * Since new tasks are assigned an initial util_avg equal to
@@ -5227,23 +5222,6 @@ enqueue_task_fair(struct rq *rq, struct task_struct *p, int flags)
 		if (flags & ENQUEUE_WAKEUP)
 			update_overutilized_status(rq);
 
-	}
-
-	if (cfs_bandwidth_used()) {
-		/*
-		 * When bandwidth control is enabled; the cfs_rq_throttled()
-		 * breaks in the above iteration can result in incomplete
-		 * leaf list maintenance, resulting in triggering the assertion
-		 * below.
-		 */
-		for_each_sched_entity(se) {
-			cfs_rq = cfs_rq_of(se);
-
-			if (list_add_leaf_cfs_rq(cfs_rq))
-				break;
-		}
-	}
-
 	assert_list_leaf_cfs_rq(rq);
 
 	hrtick_update(rq);
@@ -5258,55 +5236,21 @@ static void set_next_buddy(struct sched_entity *se);
  */
 static void dequeue_task_fair(struct rq *rq, struct task_struct *p, int flags)
 {
-	struct cfs_rq *cfs_rq;
+	struct cfs_rq *cfs_rq = &rq->cfs;
 	struct sched_entity *se = &p->se;
 	int task_sleep = flags & DEQUEUE_SLEEP;
 
 	for_each_sched_entity(se) {
-		cfs_rq = cfs_rq_of(se);
-		dequeue_entity_groups(cfs_rq, se, flags);
-		dequeue_entity(cfs_rq, se, flags);
-
-		/*
-		 * end evaluation on encountering a throttled cfs_rq
-		 *
-		 * note: in the case of encountering a throttled cfs_rq we will
-		 * post the final h_nr_running decrement below.
-		*/
-		if (cfs_rq_throttled(cfs_rq))
+		struct cfs_rq *group_rq = group_cfs_rq_of_parent(se);
+		if (!dequeue_entity_groups(group_rq, se, flags | SE_IS_CURRENT))
 			break;
-		cfs_rq->h_nr_running--;
-
-		/* Don't dequeue parent if it has other entities besides us */
-		if (cfs_rq->load.weight) {
-			/* Avoid re-evaluating load for this entity: */
-			se = parent_entity(se);
-			/*
-			 * Bias pick_next to pick a task from this cfs_rq, as
-			 * p is sleeping when it is within its sched_slice.
-			 */
-			if (task_sleep && se && !throttled_hierarchy(cfs_rq))
-				set_next_buddy(se);
-			break;
-		}
-		flags |= DEQUEUE_SLEEP;
 	}
 
-	for_each_sched_entity(se) {
-		cfs_rq = cfs_rq_of(se);
-		cfs_rq->h_nr_running--;
-
-		if (cfs_rq_throttled(cfs_rq))
-			break;
-
-		update_load_avg(cfs_rq, se, UPDATE_TG);
-		update_cfs_group(se);
-	}
+	dequeue_entity(cfs_rq, &p->se, flags);
 
-	if (!se)
-		sub_nr_running(rq, 1);
+	sub_nr_running(rq, 1);
 
-	util_est_dequeue(&rq->cfs, p, task_sleep);
+	util_est_dequeue(cfs_rq, p, task_sleep);
 	hrtick_update(rq);
 }
 
@@ -5629,7 +5573,7 @@ static unsigned long capacity_of(int cpu)
 static unsigned long cpu_avg_load_per_task(int cpu)
 {
 	struct rq *rq = cpu_rq(cpu);
-	unsigned long nr_running = READ_ONCE(rq->cfs.h_nr_running);
+	unsigned long nr_running = READ_ONCE(rq->cfs.nr_running);
 	unsigned long load_avg = weighted_cpuload(rq);
 
 	if (nr_running)
@@ -6848,11 +6792,9 @@ static void set_last_buddy(struct sched_entity *se)
 	if (entity_is_task(se) && unlikely(task_has_idle_policy(task_of(se))))
 		return;
 
-	for_each_sched_entity(se) {
-		if (SCHED_WARN_ON(!se->on_rq))
-			return;
-		cfs_rq_of(se)->last = se;
-	}
+	if (SCHED_WARN_ON(!se->on_rq))
+		return;
+	cfs_rq_of(se)->last = se;
 }
 
 static void set_next_buddy(struct sched_entity *se)
@@ -6860,17 +6802,14 @@ static void set_next_buddy(struct sched_entity *se)
 	if (entity_is_task(se) && unlikely(task_has_idle_policy(task_of(se))))
 		return;
 
-	for_each_sched_entity(se) {
-		if (SCHED_WARN_ON(!se->on_rq))
-			return;
-		cfs_rq_of(se)->next = se;
-	}
+	if (SCHED_WARN_ON(!se->on_rq))
+		return;
+	cfs_rq_of(se)->next = se;
 }
 
 static void set_skip_buddy(struct sched_entity *se)
 {
-	for_each_sched_entity(se)
-		cfs_rq_of(se)->skip = se;
+	cfs_rq_of(se)->skip = se;
 }
 
 /*
@@ -6926,7 +6865,6 @@ static void check_preempt_wakeup(struct rq *rq, struct task_struct *p, int wake_
 	if (unlikely(p->policy != SCHED_NORMAL) || !sched_feat(WAKEUP_PREEMPTION))
 		return;
 
-	find_matching_se(&se, &pse);
 	update_curr(cfs_rq_of(se));
 	BUG_ON(!pse);
 	if (wakeup_preempt_entity(se, pse) == 1) {
@@ -6967,100 +6905,18 @@ pick_next_task_fair(struct rq *rq, struct task_struct *prev, struct rq_flags *rf
 	struct task_struct *p;
 	int new_tasks;
 
+	put_prev_task(rq, prev);
 again:
 	if (!cfs_rq->nr_running)
 		goto idle;
 
-#ifdef CONFIG_FAIR_GROUP_SCHED
-	if (prev->sched_class != &fair_sched_class)
-		goto simple;
-
-	/*
-	 * Because of the set_next_buddy() in dequeue_task_fair() it is rather
-	 * likely that a next task is from the same cgroup as the current.
-	 *
-	 * Therefore attempt to avoid putting and setting the entire cgroup
-	 * hierarchy, only change the part that actually changes.
-	 */
-
-	do {
-		struct sched_entity *curr = cfs_rq->curr;
-
-		/*
-		 * Since we got here without doing put_prev_entity() we also
-		 * have to consider cfs_rq->curr. If it is still a runnable
-		 * entity, update_curr() will update its vruntime, otherwise
-		 * forget we've ever seen it.
-		 */
-		if (curr) {
-			if (curr->on_rq)
-				update_curr(cfs_rq);
-			else
-				curr = NULL;
-
-			/*
-			 * This call to check_cfs_rq_runtime() will do the
-			 * throttle and dequeue its entity in the parent(s).
-			 * Therefore the nr_running test will indeed
-			 * be correct.
-			 */
-			if (unlikely(check_cfs_rq_runtime(cfs_rq))) {
-				cfs_rq = &rq->cfs;
-
-				if (!cfs_rq->nr_running)
-					goto idle;
-
-				goto simple;
-			}
-		}
-
-		se = pick_next_entity(cfs_rq, curr);
-		cfs_rq = group_cfs_rq(se);
-	} while (cfs_rq);
-
-	p = task_of(se);
-
-	/*
-	 * Since we haven't yet done put_prev_entity and if the selected task
-	 * is a different task than we started out with, try and touch the
-	 * least amount of cfs_rqs.
-	 */
-	if (prev != p) {
-		struct sched_entity *pse = &prev->se;
-
-		while (!(cfs_rq = is_same_group(se, pse))) {
-			int se_depth = se->depth;
-			int pse_depth = pse->depth;
-
-			if (se_depth <= pse_depth) {
-				put_prev_entity(cfs_rq_of(pse), pse);
-				pse = parent_entity(pse);
-			}
-			if (se_depth >= pse_depth) {
-				set_next_entity(cfs_rq_of(se), se);
-				se = parent_entity(se);
-			}
-		}
-
-		put_prev_entity(cfs_rq, pse);
-		set_next_entity(cfs_rq, se);
-	}
-
-	goto done;
-simple:
-#endif
-
-	put_prev_task(rq, prev);
-
-	do {
-		se = pick_next_entity(cfs_rq, NULL);
-		set_next_entity(cfs_rq, se);
-		cfs_rq = group_cfs_rq(se);
-	} while (cfs_rq);
+	se = pick_next_entity(cfs_rq, NULL);
+	if (!se)
+		goto idle;
 
+	set_next_entity(cfs_rq, se);
 	p = task_of(se);
 
-done: __maybe_unused;
 #ifdef CONFIG_SMP
 	/*
 	 * Move the next running task to the front of
@@ -7109,10 +6965,8 @@ static void put_prev_task_fair(struct rq *rq, struct task_struct *prev)
 	struct sched_entity *se = &prev->se;
 	struct cfs_rq *cfs_rq;
 
-	for_each_sched_entity(se) {
-		cfs_rq = cfs_rq_of(se);
-		put_prev_entity(cfs_rq, se);
-	}
+	cfs_rq = cfs_rq_of(se);
+	put_prev_entity(cfs_rq, se);
 }
 
 /*
@@ -7877,6 +7731,11 @@ static unsigned long task_se_h_load(struct sched_entity *se)
 	return se->avg.load_avg;
 }
 
+static unsigned long task_se_h_weight(struct sched_entity *se)
+{
+	return se->load.weight;
+}
+
 static unsigned long task_se_h_weight(struct sched_entity *se)
 {
 	return se->load.weight;
@@ -8282,7 +8141,7 @@ static inline void update_sg_lb_stats(struct lb_env *env,
 
 		sgs->group_load += load;
 		sgs->group_util += cpu_util(i);
-		sgs->sum_nr_running += rq->cfs.h_nr_running;
+		sgs->sum_nr_running += rq->cfs.nr_running;
 
 		nr_running = rq->nr_running;
 		if (nr_running > 1)
@@ -8973,7 +8832,7 @@ voluntary_active_balance(struct lb_env *env)
 	 * available on dst_cpu.
 	 */
 	if ((env->idle != CPU_NOT_IDLE) &&
-	    (env->src_rq->cfs.h_nr_running == 1)) {
+	    (env->src_rq->cfs.nr_running == 1)) {
 		if ((check_cpu_capacity(env->src_rq, sd)) &&
 		    (capacity_of(env->src_cpu)*sd->imbalance_pct < capacity_of(env->dst_cpu)*100))
 			return 1;
@@ -9654,7 +9513,7 @@ static void nohz_balancer_kick(struct rq *rq)
 		 * capacity; kick the ILB to see if there's a better CPU to run
 		 * on.
 		 */
-		if (rq->cfs.h_nr_running >= 1 && check_cpu_capacity(rq, sd)) {
+		if (rq->cfs.nr_running >= 1 && check_cpu_capacity(rq, sd)) {
 			flags = NOHZ_KICK_MASK;
 			goto unlock;
 		}
@@ -10103,7 +9962,7 @@ static int idle_balance(struct rq *this_rq, struct rq_flags *rf)
 	 * have been enqueued in the meantime. Since we're not going idle,
 	 * pretend we pulled a task.
 	 */
-	if (this_rq->cfs.h_nr_running && !pulled_task)
+	if (this_rq->cfs.nr_running && !pulled_task)
 		pulled_task = 1;
 
 	/* Move the next balance forward */
@@ -10111,7 +9970,7 @@ static int idle_balance(struct rq *this_rq, struct rq_flags *rf)
 		this_rq->next_balance = next_balance;
 
 	/* Is there a task of a high priority class? */
-	if (this_rq->nr_running != this_rq->cfs.h_nr_running)
+	if (this_rq->nr_running != this_rq->cfs.nr_running)
 		pulled_task = -1;
 
 	if (pulled_task)
@@ -10198,6 +10057,10 @@ static void task_tick_fair(struct rq *rq, struct task_struct *curr, int queued)
 		entity_tick(cfs_rq, se, queued);
 	}
 
+	cfs_rq = &rq->cfs;
+	if (cfs_rq->nr_running > 1)
+		check_preempt_tick(cfs_rq, &curr->se);
+
 	if (static_branch_unlikely(&sched_numa_balancing))
 		task_tick_numa(rq, curr);
 
@@ -10296,40 +10159,51 @@ static inline bool vruntime_normalized(struct task_struct *p)
  * Propagate the changes of the sched_entity across the tg tree to make it
  * visible to the root
  */
-static void propagate_entity_cfs_rq(struct sched_entity *se)
+static void propagate_entity_cfs_rq(struct sched_entity *se, bool curr)
 {
+	unsigned long flags = UPDATE_TG;
 	struct cfs_rq *cfs_rq;
 
+	if (curr)
+		flags |= SE_IS_CURRENT;
+
 	/* Start to propagate at parent */
 	se = se->parent;
 
 	for_each_sched_entity(se) {
-		cfs_rq = cfs_rq_of(se);
+		cfs_rq = group_cfs_rq_of_parent(se);
 
 		if (cfs_rq_throttled(cfs_rq))
 			break;
 
-		update_load_avg(cfs_rq, se, UPDATE_TG);
+		if (!update_load_avg(cfs_rq, se, flags))
+			break;
 	}
 }
 #else
-static void propagate_entity_cfs_rq(struct sched_entity *se) { }
+static void propagate_entity_cfs_rq(struct sched_entity *se, bool curr) { }
 #endif
 
 static void detach_entity_cfs_rq(struct sched_entity *se)
 {
 	struct cfs_rq *cfs_rq = cfs_rq_of(se);
+	struct sched_entity *ise = se;
 
 	/* Catch up with the cfs_rq and remove our load when we leave */
-	update_load_avg(cfs_rq, se, 0);
+	for_each_sched_entity(ise) {
+		struct cfs_rq *group_rq = group_cfs_rq_of_parent(ise);
+		if (!update_load_avg(group_rq, ise, 0))
+			break;
+	}
 	detach_entity_load_avg(cfs_rq, se);
 	update_tg_load_avg(cfs_rq, false);
-	propagate_entity_cfs_rq(se);
+	propagate_entity_cfs_rq(se, true);
 }
 
 static void attach_entity_cfs_rq(struct sched_entity *se)
 {
 	struct cfs_rq *cfs_rq = cfs_rq_of(se);
+	struct sched_entity *ise = se;
 
 #ifdef CONFIG_FAIR_GROUP_SCHED
 	/*
@@ -10340,10 +10214,15 @@ static void attach_entity_cfs_rq(struct sched_entity *se)
 #endif
 
 	/* Synchronize entity with its cfs_rq */
-	update_load_avg(cfs_rq, se, sched_feat(ATTACH_AGE_LOAD) ? 0 : SKIP_AGE_LOAD);
+	for_each_sched_entity(ise) {
+		struct cfs_rq *group_rq = group_cfs_rq_of_parent(ise);
+		int flags = sched_feat(ATTACH_AGE_LOAD) ? 0 : SKIP_AGE_LOAD;
+		if (!update_load_avg(group_rq, ise, flags))
+			break;
+	}
 	attach_entity_load_avg(cfs_rq, se, 0);
 	update_tg_load_avg(cfs_rq, false);
-	propagate_entity_cfs_rq(se);
+	propagate_entity_cfs_rq(se, false);
 }
 
 static void detach_task_cfs_rq(struct task_struct *p)
@@ -10404,14 +10283,11 @@ static void switched_to_fair(struct rq *rq, struct task_struct *p)
 static void set_curr_task_fair(struct rq *rq)
 {
 	struct sched_entity *se = &rq->curr->se;
+	struct cfs_rq *cfs_rq = cfs_rq_of(se);
 
-	for_each_sched_entity(se) {
-		struct cfs_rq *cfs_rq = cfs_rq_of(se);
-
-		set_next_entity(cfs_rq, se);
-		/* ensure bandwidth has been allocated on our new cfs_rq */
-		account_cfs_rq_runtime(cfs_rq, 0);
-	}
+	set_next_entity(cfs_rq, se);
+	/* ensure bandwidth has been allocated on our new cfs_rq */
+	account_cfs_rq_runtime(cfs_rq, 0);
 }
 
 void init_cfs_rq(struct cfs_rq *cfs_rq)
diff --git a/kernel/sched/pelt.c b/kernel/sched/pelt.c
index 190797e421dd..2c901e0f9fbd 100644
--- a/kernel/sched/pelt.c
+++ b/kernel/sched/pelt.c
@@ -266,10 +266,10 @@ int __update_load_avg_blocked_se(u64 now, struct sched_entity *se)
 	return 0;
 }
 
-int __update_load_avg_se(u64 now, struct cfs_rq *cfs_rq, struct sched_entity *se)
+int __update_load_avg_se(u64 now, struct cfs_rq *cfs_rq, struct sched_entity *se, bool load, bool running)
 {
-	if (___update_load_sum(now, &se->avg, !!se->on_rq,
-				cfs_rq->curr == se)) {
+	if (___update_load_sum(now, &se->avg, (!!se->on_rq || load),
+				(cfs_rq->curr == se) || running)) {
 
 		___update_load_avg(&se->avg, se_weight(se));
 		cfs_se_util_change(&se->avg);
diff --git a/kernel/sched/pelt.h b/kernel/sched/pelt.h
index 7489d5f56960..1152c4ebf314 100644
--- a/kernel/sched/pelt.h
+++ b/kernel/sched/pelt.h
@@ -2,7 +2,7 @@
 #include "sched-pelt.h"
 
 int __update_load_avg_blocked_se(u64 now, struct sched_entity *se);
-int __update_load_avg_se(u64 now, struct cfs_rq *cfs_rq, struct sched_entity *se);
+int __update_load_avg_se(u64 now, struct cfs_rq *cfs_rq, struct sched_entity *se, bool load, bool running);
 int __update_load_avg_cfs_rq(u64 now, struct cfs_rq *cfs_rq);
 int update_rt_rq_load_avg(u64 now, struct rq *rq, int running);
 int update_dl_rq_load_avg(u64 now, struct rq *rq, int running);
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 4f8acbab0fb2..62c56ae6ce57 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -1444,7 +1444,7 @@ static inline void set_task_rq(struct task_struct *p, unsigned int cpu)
 
 #ifdef CONFIG_FAIR_GROUP_SCHED
 	set_task_rq_fair(&p->se, p->se.cfs_rq, tg->cfs_rq[cpu]);
-	p->se.cfs_rq = tg->cfs_rq[cpu];
+	p->se.cfs_rq = &cpu_rq(cpu)->cfs;
 	p->se.parent = tg->se[cpu];
 #endif
 
-- 
2.20.1

Re: [PATCH 03/10] sched,fair: redefine runnable_load_avg as the sum of task_h_load

[Josef Bacik]

On Fri, Jun 28, 2019 at 04:49:06PM -0400, Rik van Riel wrote:
> The runnable_load magic is used to quickly propagate information about
> runnable tasks up the hierarchy of runqueues. The runnable_load_avg is
> mostly used for the load balancing code, which only examines the value at
> the root cfs_rq.
> 
> Redefine the root cfs_rq runnable_load_avg to be the sum of task_h_loads
> of the runnable tasks. This works because the hierarchical runnable_load of
> a task is already equal to the task_se_h_load today. This provides enough
> information to the load balancer.
> 
> The runnable_load_avg of the cgroup cfs_rqs does not appear to be
> used for anything, so don't bother calculating those.
> 
> This removes one of the things that the code currently traverses the
> cgroup hierarchy for, and getting rid of it brings us one step closer
> to a flat runqueue for the CPU controller.
> 

My memory on this stuff is very hazy, but IIRC we had the runnable_sum and the
runnable_avg separated out because you could have the avg lag behind the sum.
So like you enqueue a bunch of new entities who's avg may have decayed a bunch
and so their overall load is not felt on the CPU until they start running, and
now you've overloaded that CPU.  The sum was there to make sure new things
coming onto the CPU added actual load to the queue instead of looking like there
was no load.

Is this going to be a problem now with this new code?

<snip>

> +static inline void
> +update_runnable_load_avg(struct sched_entity *se)
> +{
> +	struct cfs_rq *root_cfs_rq = &cfs_rq_of(se)->rq->cfs;
> +	long new_h_load, delta;
> +
> +	SCHED_WARN_ON(!entity_is_task(se));
> +
> +	if (!se->on_rq)
> +		return;
>  
> -	sub_positive(&cfs_rq->avg.runnable_load_avg, se->avg.runnable_load_avg);
> -	sub_positive(&cfs_rq->avg.runnable_load_sum,
> -		     se_runnable(se) * se->avg.runnable_load_sum);
> +	new_h_load = task_se_h_load(se);
> +	delta = new_h_load - se->enqueued_h_load;
> +	root_cfs_rq->avg.runnable_load_avg += delta;

Should we use add_positive here?  Thanks,

Josef

Re: [PATCH 03/10] sched,fair: redefine runnable_load_avg as the sum of task_h_load

[Rik van Riel]

[-- Attachment #1: Type: text/plain, Size: 2801 bytes --]

On Mon, 2019-07-01 at 12:29 -0400, Josef Bacik wrote:
> On Fri, Jun 28, 2019 at 04:49:06PM -0400, Rik van Riel wrote:
> > The runnable_load magic is used to quickly propagate information
> > about
> > runnable tasks up the hierarchy of runqueues. The runnable_load_avg
> > is
> > mostly used for the load balancing code, which only examines the
> > value at
> > the root cfs_rq.
> > 
> > Redefine the root cfs_rq runnable_load_avg to be the sum of
> > task_h_loads
> > of the runnable tasks. This works because the hierarchical
> > runnable_load of
> > a task is already equal to the task_se_h_load today. This provides
> > enough
> > information to the load balancer.
> > 
> > The runnable_load_avg of the cgroup cfs_rqs does not appear to be
> > used for anything, so don't bother calculating those.
> > 
> > This removes one of the things that the code currently traverses
> > the
> > cgroup hierarchy for, and getting rid of it brings us one step
> > closer
> > to a flat runqueue for the CPU controller.
> > 
> 
> My memory on this stuff is very hazy, but IIRC we had the
> runnable_sum and the
> runnable_avg separated out because you could have the avg lag behind
> the sum.
> So like you enqueue a bunch of new entities who's avg may have
> decayed a bunch
> and so their overall load is not felt on the CPU until they start
> running, and
> now you've overloaded that CPU.  The sum was there to make sure new
> things
> coming onto the CPU added actual load to the queue instead of looking
> like there
> was no load.
> 
> Is this going to be a problem now with this new code?

That is a good question!

On the one hand, you may well be right.

On the other hand, while I see the old code calculating
runnable_sum, I don't really see it _using_ it to drive
scheduling decisions.

It would be easy to define the CPU cfs_rq->runnable_load_sum
as being the sum of task_se_h_weight() of each runnable task
on the CPU (for example), but what would we use it for?

What am I missing?

> +static inline void
> > +update_runnable_load_avg(struct sched_entity *se)
> > +{
> > +	struct cfs_rq *root_cfs_rq = &cfs_rq_of(se)->rq->cfs;
> > +	long new_h_load, delta;
> > +
> > +	SCHED_WARN_ON(!entity_is_task(se));
> > +
> > +	if (!se->on_rq)
> > +		return;
> >  
> > -	sub_positive(&cfs_rq->avg.runnable_load_avg, se-
> > >avg.runnable_load_avg);
> > -	sub_positive(&cfs_rq->avg.runnable_load_sum,
> > -		     se_runnable(se) * se->avg.runnable_load_sum);
> > +	new_h_load = task_se_h_load(se);
> > +	delta = new_h_load - se->enqueued_h_load;
> > +	root_cfs_rq->avg.runnable_load_avg += delta;
> 
> Should we use add_positive here?  Thanks,

Yes, we should use add_positive. I'll do that for v3.

-- 
All Rights Reversed.

[-- Attachment #2: This is a digitally signed message part --]
[-- Type: application/pgp-signature, Size: 488 bytes --]

Re: [PATCH 03/10] sched,fair: redefine runnable_load_avg as the sum of task_h_load

[Josef Bacik]

On Mon, Jul 01, 2019 at 12:47:35PM -0400, Rik van Riel wrote:
> On Mon, 2019-07-01 at 12:29 -0400, Josef Bacik wrote:
> > On Fri, Jun 28, 2019 at 04:49:06PM -0400, Rik van Riel wrote:
> > > The runnable_load magic is used to quickly propagate information
> > > about
> > > runnable tasks up the hierarchy of runqueues. The runnable_load_avg
> > > is
> > > mostly used for the load balancing code, which only examines the
> > > value at
> > > the root cfs_rq.
> > > 
> > > Redefine the root cfs_rq runnable_load_avg to be the sum of
> > > task_h_loads
> > > of the runnable tasks. This works because the hierarchical
> > > runnable_load of
> > > a task is already equal to the task_se_h_load today. This provides
> > > enough
> > > information to the load balancer.
> > > 
> > > The runnable_load_avg of the cgroup cfs_rqs does not appear to be
> > > used for anything, so don't bother calculating those.
> > > 
> > > This removes one of the things that the code currently traverses
> > > the
> > > cgroup hierarchy for, and getting rid of it brings us one step
> > > closer
> > > to a flat runqueue for the CPU controller.
> > > 
> > 
> > My memory on this stuff is very hazy, but IIRC we had the
> > runnable_sum and the
> > runnable_avg separated out because you could have the avg lag behind
> > the sum.
> > So like you enqueue a bunch of new entities who's avg may have
> > decayed a bunch
> > and so their overall load is not felt on the CPU until they start
> > running, and
> > now you've overloaded that CPU.  The sum was there to make sure new
> > things
> > coming onto the CPU added actual load to the queue instead of looking
> > like there
> > was no load.
> > 
> > Is this going to be a problem now with this new code?
> 
> That is a good question!
> 
> On the one hand, you may well be right.
> 
> On the other hand, while I see the old code calculating
> runnable_sum, I don't really see it _using_ it to drive
> scheduling decisions.
> 
> It would be easy to define the CPU cfs_rq->runnable_load_sum
> as being the sum of task_se_h_weight() of each runnable task
> on the CPU (for example), but what would we use it for?
> 
> What am I missing?

It's suuuuuper sublte, but you're right in that we don't really need the
runnable_avg per-se, but what you do is you kill calc_group_runnable, which used
to do this

load_avg = max(cfs_rq->avg.load_avg,
               scale_load_down(cfs_rq->load.weight));

runnable = max(cfs_rq->avg.runnable_load_avg,
               scale_load_down(cfs_rq->runnable_weight));

so we'd account for this weirdness of adding a previously idle process to a new
CPU and overloading the CPU because we'd add a bunch of these 0 weight looking
tasks that suddenly all wake up and are on the same CPU.  So we used the
runnable_weight to account for what was actually happening, and the max of
load_avg and the weight to figure out what the potential load would be.

What you've done here is change the weighting stuff to be completely based on
load avg, which is problematic for the reasons above.  Did you fix this later on
in your patches?  If so then just tell me to keep reading and I'll do that ;).
Thanks,

Josef

Re: [PATCH 03/10] sched,fair: redefine runnable_load_avg as the sum of task_h_load

[Rik van Riel]

[-- Attachment #1: Type: text/plain, Size: 2626 bytes --]

On Mon, 2019-07-01 at 15:22 -0400, Josef Bacik wrote:
> On Mon, Jul 01, 2019 at 12:47:35PM -0400, Rik van Riel wrote:
> > On Mon, 2019-07-01 at 12:29 -0400, Josef Bacik wrote:
> > > 
> > > My memory on this stuff is very hazy, but IIRC we had the
> > > runnable_sum and the
> > > runnable_avg separated out because you could have the avg lag
> > > behind
> > > the sum.
> > > So like you enqueue a bunch of new entities who's avg may have
> > > decayed a bunch
> > > and so their overall load is not felt on the CPU until they start
> > > running, and
> > > now you've overloaded that CPU.  The sum was there to make sure
> > > new
> > > things
> > > coming onto the CPU added actual load to the queue instead of
> > > looking
> > > like there
> > > was no load.
> > > 
> > > Is this going to be a problem now with this new code?
> > 
> > That is a good question!
> > 
> > On the one hand, you may well be right.
> > 
> > On the other hand, while I see the old code calculating
> > runnable_sum, I don't really see it _using_ it to drive
> > scheduling decisions.
> > 
> > It would be easy to define the CPU cfs_rq->runnable_load_sum
> > as being the sum of task_se_h_weight() of each runnable task
> > on the CPU (for example), but what would we use it for?
> > 
> > What am I missing?
> 
> It's suuuuuper sublte, but you're right in that we don't really need
> the
> runnable_avg per-se, but what you do is you kill calc_group_runnable,
> which used
> to do this
> 
> load_avg = max(cfs_rq->avg.load_avg,
>                scale_load_down(cfs_rq->load.weight));
> 
> runnable = max(cfs_rq->avg.runnable_load_avg,
>                scale_load_down(cfs_rq->runnable_weight));
> 
> so we'd account for this weirdness of adding a previously idle
> process to a new
> CPU and overloading the CPU because we'd add a bunch of these 0
> weight looking
> tasks that suddenly all wake up and are on the same CPU.  So we used
> the
> runnable_weight to account for what was actually happening, and the
> max of
> load_avg and the weight to figure out what the potential load would
> be.
> 
> What you've done here is change the weighting stuff to be completely
> based on
> load avg, which is problematic for the reasons above.  Did you fix
> this later on
> in your patches?  If so then just tell me to keep reading and I'll do
> that ;).

No, I have not fixed that later in the code.

I am not entirely sure how I could do that, without
reintroducing walking the hierarchy at task enqueue
and dequeue, but maybe you have some idea...

-- 
All Rights Reversed.

[-- Attachment #2: This is a digitally signed message part --]
[-- Type: application/pgp-signature, Size: 488 bytes --]

Re: [PATCH 01/10] sched: introduce task_se_h_load helper

[Josef Bacik]

On Fri, Jun 28, 2019 at 04:49:04PM -0400, Rik van Riel wrote:
> Sometimes the hierarchical load of a sched_entity needs to be calculated.
> Rename task_h_load to task_se_h_load, and directly pass a sched_entity to
> that function.
> 
> Move the function declaration up above where it will be used later.
> 
> No functional changes.
> 
> Signed-off-by: Rik van Riel <riel@surriel.com>

Reviewed-by: Josef Bacik <josef@toxicpanda.com>

Thanks,

Josef

Re: [PATCH 02/10] sched: change /proc/sched_debug fields

[Josef Bacik]

On Fri, Jun 28, 2019 at 04:49:05PM -0400, Rik van Riel wrote:
> Remove some fields from /proc/sched_debug that are removed from
> sched_entity in a subsequent patch, and add h_load, which comes in
> very handy to debug CPU controller weight distribution.
> 
> Signed-off-by: Rik van Riel <riel@surriel.com>

Reviewed-by: Josef Bacik <josef@toxicpanda.com>

Thanks,

Josef

Re: [PATCH 09/10] sched,fair: add helper functions for flattened runqueue

[Josef Bacik]

On Fri, Jun 28, 2019 at 04:49:12PM -0400, Rik van Riel wrote:
> Add helper functions to make the flattened runqueue patch a little smaller.
> 
> The task_se_h_weight function is similar to task_se_h_load, but scales the
> task weight by the group weight, without taking the task's duty cycle into
> account.
> 
> The task_se_in_cgroup helper is functionally identical to parent_entity,
> but directly calling a function with that name obscures what the other
> code is trying to use it for, and would make the code harder to understand.
> 
> Signed-off-by: Rik van Riel <riel@surriel.com>
> ---
>  kernel/sched/fair.c | 26 ++++++++++++++++++++++++++
>  1 file changed, 26 insertions(+)
> 
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index a751e7a9b228..6fea8849cc12 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -243,6 +243,7 @@ static u64 __calc_delta(u64 delta_exec, unsigned long weight, struct load_weight
>  
>  const struct sched_class fair_sched_class;
>  static unsigned long task_se_h_load(struct sched_entity *se);
> +static unsigned long task_se_h_weight(struct sched_entity *se);
>  
>  /**************************************************************
>   * CFS operations on generic schedulable entities:
> @@ -411,6 +412,12 @@ static inline struct sched_entity *parent_entity(struct sched_entity *se)
>  	return se->parent;
>  }
>  
> +/* Is this (task) sched_entity in a non-root cgroup? */
> +static inline bool task_se_in_cgroup(struct sched_entity *se)
> +{
> +	return parent_entity(se);
> +}
> +
>  static void
>  find_matching_se(struct sched_entity **se, struct sched_entity **pse)
>  {
> @@ -7819,6 +7826,20 @@ static void update_cfs_rq_h_load(struct cfs_rq *cfs_rq)
>  	}
>  }
>  
> +static unsigned long task_se_h_weight(struct sched_entity *se)
> +{
> +	struct cfs_rq *cfs_rq;
> +
> +	if (!task_se_in_cgroup(se))
> +		return se->load.weight;
> +
> +	cfs_rq = group_cfs_rq_of_parent(se);
> +	update_cfs_rq_h_load(cfs_rq);
> +
> +	/* Reduce the load.weight by the h_load of the group the task is in. */
> +	return (cfs_rq->h_load * se->load.weight) >> SCHED_FIXEDPOINT_SHIFT;

This should be

scale_load_down(cfs_rq->h_load * se->load.weight);

Thanks,

Josef

Re: [PATCH 10/10] sched,fair: flatten hierarchical runqueues

[Josef Bacik]

On Fri, Jun 28, 2019 at 04:49:13PM -0400, Rik van Riel wrote:
> Flatten the hierarchical runqueues into just the per CPU rq.cfs runqueue.
> 
> Iteration of the sched_entity hierarchy is rate limited to once per jiffy
> per sched_entity, which is a smaller change than it seems, because load
> average adjustments were already rate limited to once per jiffy before this
> patch series.
> 
> This patch breaks CONFIG_CFS_BANDWIDTH. The plan for that is to park tasks
> from throttled cgroups onto their cgroup runqueues, and slowly (using the
> GENTLE_FAIR_SLEEPERS) wake them back up, in vruntime order, once the cgroup
> gets unthrottled, to prevent thundering herd issues.
> 
> Signed-off-by: Rik van Riel <riel@surriel.com>
> ---
>  include/linux/sched.h |   2 +
>  kernel/sched/fair.c   | 452 +++++++++++++++---------------------------
>  kernel/sched/pelt.c   |   6 +-
>  kernel/sched/pelt.h   |   2 +-
>  kernel/sched/sched.h  |   2 +-
>  5 files changed, 171 insertions(+), 293 deletions(-)
> 
> diff --git a/include/linux/sched.h b/include/linux/sched.h
> index 84a6cc6f5c47..901c710363e7 100644
> --- a/include/linux/sched.h
> +++ b/include/linux/sched.h
> @@ -453,6 +453,8 @@ struct sched_entity {
>  #ifdef CONFIG_FAIR_GROUP_SCHED
>  	int				depth;
>  	unsigned long			enqueued_h_load;
> +	unsigned long			enqueued_h_weight;
> +	struct load_weight		h_load;
>  	struct sched_entity		*parent;
>  	/* rq on which this entity is (to be) queued: */
>  	struct cfs_rq			*cfs_rq;
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index 6fea8849cc12..c31d3da081fb 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -450,6 +450,19 @@ find_matching_se(struct sched_entity **se, struct sched_entity **pse)
>  	}
>  }
>  
> +/* Add the cgroup cfs_rqs to the list, for update_blocked_averages */
> +static void enqueue_entity_cfs_rqs(struct sched_entity *se)
> +{
> +	SCHED_WARN_ON(!entity_is_task(se));
> +
> +	for_each_sched_entity(se) {
> +		struct cfs_rq *cfs_rq = group_cfs_rq_of_parent(se);
> +
> +		if (list_add_leaf_cfs_rq(cfs_rq))
> +			break;
> +	}
> +}
> +
>  #else	/* !CONFIG_FAIR_GROUP_SCHED */
>  
>  static inline struct task_struct *task_of(struct sched_entity *se)
> @@ -672,8 +685,14 @@ int sched_proc_update_handler(struct ctl_table *table, int write,
>   */
>  static inline u64 calc_delta_fair(u64 delta, struct sched_entity *se)
>  {
> -	if (unlikely(se->load.weight != NICE_0_LOAD))
> +	if (task_se_in_cgroup(se)) {
> +		unsigned long h_weight = task_se_h_weight(se);
> +		if (h_weight != se->h_load.weight)
> +			update_load_set(&se->h_load, h_weight);
> +		delta = __calc_delta(delta, NICE_0_LOAD, &se->h_load);
> +	} else if (unlikely(se->load.weight != NICE_0_LOAD)) {
>  		delta = __calc_delta(delta, NICE_0_LOAD, &se->load);
> +	}
>  
>  	return delta;
>  }
> @@ -687,22 +706,16 @@ static inline u64 calc_delta_fair(u64 delta, struct sched_entity *se)
>  static u64 sched_slice(struct cfs_rq *cfs_rq, struct sched_entity *se)
>  {
>  	u64 slice = sysctl_sched_latency;
> +	struct load_weight *load = &cfs_rq->load;
> +	struct load_weight lw;
>  
> -	for_each_sched_entity(se) {
> -		struct load_weight *load;
> -		struct load_weight lw;
> -
> -		cfs_rq = cfs_rq_of(se);
> -		load = &cfs_rq->load;
> +	if (unlikely(!se->on_rq)) {
> +		lw = cfs_rq->load;
>  
> -		if (unlikely(!se->on_rq)) {
> -			lw = cfs_rq->load;
> -
> -			update_load_add(&lw, se->load.weight);
> -			load = &lw;
> -		}
> -		slice = __calc_delta(slice, se->load.weight, load);
> +		update_load_add(&lw, task_se_h_weight(se));
> +		load = &lw;
>  	}
> +	slice = __calc_delta(slice, task_se_h_weight(se), load);
>  
>  	/*
>  	 * To avoid cache thrashing, run at least sysctl_sched_min_granularity.
> @@ -2703,16 +2716,28 @@ static inline void update_scan_period(struct task_struct *p, int new_cpu)
>  static void
>  account_entity_enqueue(struct cfs_rq *cfs_rq, struct sched_entity *se)
>  {
> -	update_load_add(&cfs_rq->load, se->load.weight);
> -	if (!parent_entity(se))
> +	struct rq *rq;
> +
> +	if (task_se_in_cgroup(se)) {
> +		struct cfs_rq *cgroup_rq = group_cfs_rq_of_parent(se);
> +		unsigned long h_weight;
> +
> +		update_load_add(&cgroup_rq->load, se->load.weight);
> +		cgroup_rq->nr_running++;
> +
> +		/* Add the hierarchical weight to the CPU rq */
> +		h_weight = task_se_h_weight(se);
> +		se->enqueued_h_weight = h_weight;
> +		update_load_add(&rq_of(cfs_rq)->load, h_weight);

Ok I think this is where we need to handle the newly enqueued se's potential
weight.  Right now task_se_h_weight() is based on it's weight _and_ its load.
So it's really it's task_se_h_weighted_load_avg, and not really
task_se_h_weight, right?  Instead we should separate these two things out, one
gives us our heirarchal load, and one that gives us our heirarchal weight based
purely on the ratio of (our weight) / (total se weight on parent).  Then we can
take this number and max it with the heirarchal load avg and use that with the
update_load_add.  Does that make sense?  Thanks,

Josef

Re: [PATCH 09/10] sched,fair: add helper functions for flattened runqueue

[Rik van Riel]

[-- Attachment #1: Type: text/plain, Size: 867 bytes --]

On Mon, 2019-07-01 at 16:20 -0400, Josef Bacik wrote:
> 
> 
> > +static unsigned long task_se_h_weight(struct sched_entity *se)
> > +{
> > +	struct cfs_rq *cfs_rq;
> > +
> > +	if (!task_se_in_cgroup(se))
> > +		return se->load.weight;
> > +
> > +	cfs_rq = group_cfs_rq_of_parent(se);
> > +	update_cfs_rq_h_load(cfs_rq);
> > +
> > +	/* Reduce the load.weight by the h_load of the group the task
> > is in. */
> > +	return (cfs_rq->h_load * se->load.weight) >>
> > SCHED_FIXEDPOINT_SHIFT;
> 
> This should be
> 
> scale_load_down(cfs_rq->h_load * se->load.weight);

That may be the same mathematically, but it is
different conceptually.

If we convert CFS to have full load resolution with
cgroups (which we probably want), then scale_load_down
becomes a noop, while this shift continues doing the
right thing.

-- 
All Rights Reversed.

[-- Attachment #2: This is a digitally signed message part --]
[-- Type: application/pgp-signature, Size: 488 bytes --]

Re: [PATCH 10/10] sched,fair: flatten hierarchical runqueues

[Rik van Riel]

[-- Attachment #1: Type: text/plain, Size: 2141 bytes --]

On Mon, 2019-07-01 at 16:34 -0400, Josef Bacik wrote:
> On Fri, Jun 28, 2019 at 04:49:13PM -0400, Rik van Riel wrote:
> > @@ -2703,16 +2716,28 @@ static inline void
> > update_scan_period(struct task_struct *p, int new_cpu)
> >  static void
> >  account_entity_enqueue(struct cfs_rq *cfs_rq, struct sched_entity
> > *se)
> >  {
> > -	update_load_add(&cfs_rq->load, se->load.weight);
> > -	if (!parent_entity(se))
> > +	struct rq *rq;
> > +
> > +	if (task_se_in_cgroup(se)) {
> > +		struct cfs_rq *cgroup_rq = group_cfs_rq_of_parent(se);
> > +		unsigned long h_weight;
> > +
> > +		update_load_add(&cgroup_rq->load, se->load.weight);
> > +		cgroup_rq->nr_running++;
> > +
> > +		/* Add the hierarchical weight to the CPU rq */
> > +		h_weight = task_se_h_weight(se);
> > +		se->enqueued_h_weight = h_weight;
> > +		update_load_add(&rq_of(cfs_rq)->load, h_weight);
> 
> Ok I think this is where we need to handle the newly enqueued se's
> potential
> weight.  Right now task_se_h_weight() is based on it's weight _and_
> its load.
> So it's really it's task_se_h_weighted_load_avg, and not really
> task_se_h_weight, right?  Instead we should separate these two things
> out, one
> gives us our heirarchal load, and one that gives us our heirarchal
> weight based
> purely on the ratio of (our weight) / (total se weight on
> parent).  Then we can
> take this number and max it with the heirarchal load avg and use that
> with the
> update_load_add.  Does that make sense?  Thanks,

Yes, I think that makes sense.

The hierarchical group weights can be computed periodically,
in the same way the hierarchical group load averages are.

We may still end up with stale values occasionally, if the
values were already computed the same jiffy, or when the
values of another group (with a shared parent) have not been
propagated up yet, but things should converge relatively
quickly.

It means update_cfs_rq_h_load() and update_blocked_averages()
will propagate both load averages and instantaneous weights,
which should be easy enough to add.

I'll give it a try!

-- 
All Rights Reversed.

[-- Attachment #2: This is a digitally signed message part --]
[-- Type: application/pgp-signature, Size: 488 bytes --]

Re: [PATCH 05/10] sched,fair: remove cfs rqs from leaf_cfs_rq_list bottom up

[Vincent Guittot]

On Fri, 28 Jun 2019 at 22:49, Rik van Riel <riel@surriel.com> wrote:
>
> Reducing the overhead of the CPU controller is achieved by not walking
> all the sched_entities every time a task is enqueued or dequeued.
>
> One of the things being checked every single time is whether the cfs_rq
> is on the rq->leaf_cfs_rq_list.
>
> By only removing a cfs_rq from the list once it no longer has children
> on the list, we can avoid walking the sched_entity hierarchy if the bottom
> cfs_rq is on the list, once the runqueues have been flattened.
>
> Signed-off-by: Rik van Riel <riel@surriel.com>
> ---
>  kernel/sched/fair.c  | 17 +++++++++++++++++
>  kernel/sched/sched.h |  1 +
>  2 files changed, 18 insertions(+)
>
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index 63cb40253b26..e41feacc45d9 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -286,6 +286,13 @@ static inline bool list_add_leaf_cfs_rq(struct cfs_rq *cfs_rq)
>
>         cfs_rq->on_list = 1;
>
> +       /*
> +        * If the tmp_alone_branch cursor was moved, it means a child cfs_rq
> +        * is already on the list ahead of us.
> +        */
> +       if (rq->tmp_alone_branch != &rq->leaf_cfs_rq_list)
> +               cfs_rq->children_on_list++;
> +
>         /*
>          * Ensure we either appear before our parent (if already
>          * enqueued) or force our parent to appear after us when it is
> @@ -311,6 +318,7 @@ static inline bool list_add_leaf_cfs_rq(struct cfs_rq *cfs_rq)
>                  * list.
>                  */
>                 rq->tmp_alone_branch = &rq->leaf_cfs_rq_list;
> +               cfs_rq->tg->parent->cfs_rq[cpu]->children_on_list++;
>                 return true;
>         }
>
> @@ -359,6 +367,11 @@ static inline void list_del_leaf_cfs_rq(struct cfs_rq *cfs_rq)
>                 if (rq->tmp_alone_branch == &cfs_rq->leaf_cfs_rq_list)
>                         rq->tmp_alone_branch = cfs_rq->leaf_cfs_rq_list.prev;
>
> +               if (cfs_rq->tg->parent) {
> +                       int cpu = cpu_of(rq);
> +                       cfs_rq->tg->parent->cfs_rq[cpu]->children_on_list--;
> +               }
> +
>                 list_del_rcu(&cfs_rq->leaf_cfs_rq_list);
>                 cfs_rq->on_list = 0;
>         }
> @@ -7687,6 +7700,10 @@ static inline bool cfs_rq_is_decayed(struct cfs_rq *cfs_rq)
>         if (cfs_rq->avg.util_sum)
>                 return false;
>
> +       /* Remove decayed parents once their decayed children are gone. */
> +       if (cfs_rq->children_on_list)

I'm not sure that you really need to count whether childrens are on the list.
Instead you can take advantage of the list ordering and you only have
to test if the previous cfs_rq in the list is a child. If it's not
then there is no more child

and you can remove the new field children_on_list and inc/dec it

> +               return false;
> +
>         return true;
>  }
>
> diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
> index 32978a8de8ce..4f8acbab0fb2 100644
> --- a/kernel/sched/sched.h
> +++ b/kernel/sched/sched.h
> @@ -557,6 +557,7 @@ struct cfs_rq {
>          * This list is used during load balance.
>          */
>         int                     on_list;
> +       int                     children_on_list;
>         struct list_head        leaf_cfs_rq_list;
>         struct task_group       *tg;    /* group that "owns" this runqueue */
>
> --
> 2.20.1
>

Re: [PATCH 05/10] sched,fair: remove cfs rqs from leaf_cfs_rq_list bottom up

[Rik van Riel]

[-- Attachment #1: Type: text/plain, Size: 1004 bytes --]

On Thu, 2019-07-04 at 11:33 +0200, Vincent Guittot wrote:
> On Fri, 28 Jun 2019 at 22:49, Rik van Riel <riel@surriel.com> wrote:
> > Reducing the overhead of the CPU controller is achieved by not
> > walking
> > all the sched_entities every time a task is enqueued or dequeued.

> > @@ -7687,6 +7700,10 @@ static inline bool cfs_rq_is_decayed(struct
> > cfs_rq *cfs_rq)
> >         if (cfs_rq->avg.util_sum)
> >                 return false;
> > 
> > +       /* Remove decayed parents once their decayed children are
> > gone. */
> > +       if (cfs_rq->children_on_list)
> 
> I'm not sure that you really need to count whether childrens are on
> the list.
> Instead you can take advantage of the list ordering and you only have
> to test if the previous cfs_rq in the list is a child. If it's not
> then there is no more child
> 
> and you can remove the new field children_on_list and inc/dec it

Good suggestion. I'll do that for v3.

Thank you.

-- 
All Rights Reversed.

[-- Attachment #2: This is a digitally signed message part --]
[-- Type: application/pgp-signature, Size: 488 bytes --]

Re: [PATCH 07/10] sched,cfs: fix zero length timeslice calculation

[Vincent Guittot]

On Fri, 28 Jun 2019 at 22:49, Rik van Riel <riel@surriel.com> wrote:
>
> The way the time slice length is currently calculated, not only do high
> priority tasks get longer time slices than low priority tasks, but due
> to fixed point math, low priority tasks could end up with a zero length
> time slice. This can lead to cache thrashing and other inefficiencies.
>
> Simplify the logic a little bit, and cap the minimum time slice length
> to sysctl_sched_min_granularity.
>
> Tasks that end up getting a time slice length too long for their relative
> priority will simply end up having their vruntime advanced much faster than
> other tasks, resulting in them receiving time slices less frequently.
>
> Signed-off-by: Rik van Riel <riel@surriel.com>
> ---
>  kernel/sched/fair.c | 25 ++++++++-----------------
>  1 file changed, 8 insertions(+), 17 deletions(-)
>
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index d48bff5118fc..8da2823401ca 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -671,22 +671,6 @@ static inline u64 calc_delta_fair(u64 delta, struct sched_entity *se)
>         return delta;
>  }
>
> -/*
> - * The idea is to set a period in which each task runs once.
> - *
> - * When there are too many tasks (sched_nr_latency) we have to stretch
> - * this period because otherwise the slices get too small.
> - *
> - * p = (nr <= nl) ? l : l*nr/nl
> - */
> -static u64 __sched_period(unsigned long nr_running)
> -{
> -       if (unlikely(nr_running > sched_nr_latency))
> -               return nr_running * sysctl_sched_min_granularity;
> -       else
> -               return sysctl_sched_latency;
> -}
> -
>  /*
>   * We calculate the wall-time slice from the period by taking a part
>   * proportional to the weight.
> @@ -695,7 +679,7 @@ static u64 __sched_period(unsigned long nr_running)
>   */
>  static u64 sched_slice(struct cfs_rq *cfs_rq, struct sched_entity *se)
>  {
> -       u64 slice = __sched_period(cfs_rq->nr_running + !se->on_rq);
> +       u64 slice = sysctl_sched_latency;

Is the change above and the remove of __sched_period() really needed
for fixing the null time slice problem ?
This change impacts how tasks will preempt each other and as a result
the throughput. It should have it dedicated patch so we can evaluate
its impact

>
>         for_each_sched_entity(se) {
>                 struct load_weight *load;
> @@ -712,6 +696,13 @@ static u64 sched_slice(struct cfs_rq *cfs_rq, struct sched_entity *se)
>                 }
>                 slice = __calc_delta(slice, se->load.weight, load);
>         }
> +
> +       /*
> +        * To avoid cache thrashing, run at least sysctl_sched_min_granularity.
> +        * The vruntime of a low priority task advances faster; those tasks
> +        * will simply get time slices less frequently.
> +        */
> +       slice = max_t(u64, slice, sysctl_sched_min_granularity);
>         return slice;
>  }
>
> --
> 2.20.1
>

Re: [PATCH 07/10] sched,cfs: fix zero length timeslice calculation

[Rik van Riel]

[-- Attachment #1: Type: text/plain, Size: 2717 bytes --]

On Fri, 2019-07-05 at 16:51 +0200, Vincent Guittot wrote:
> On Fri, 28 Jun 2019 at 22:49, Rik van Riel <riel@surriel.com> wrote:
> > The way the time slice length is currently calculated, not only do
> > high
> > priority tasks get longer time slices than low priority tasks, but
> > due
> > to fixed point math, low priority tasks could end up with a zero
> > length
> > time slice. This can lead to cache thrashing and other
> > inefficiencies.
> > 
> > Simplify the logic a little bit, and cap the minimum time slice
> > length
> > to sysctl_sched_min_granularity.
> > 
> > Tasks that end up getting a time slice length too long for their
> > relative
> > priority will simply end up having their vruntime advanced much
> > faster than
> > other tasks, resulting in them receiving time slices less
> > frequently.
> > 
> > Signed-off-by: Rik van Riel <riel@surriel.com>
> > ---
> >  kernel/sched/fair.c | 25 ++++++++-----------------
> >  1 file changed, 8 insertions(+), 17 deletions(-)
> > 
> > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> > index d48bff5118fc..8da2823401ca 100644
> > --- a/kernel/sched/fair.c
> > +++ b/kernel/sched/fair.c
> > @@ -671,22 +671,6 @@ static inline u64 calc_delta_fair(u64 delta,
> > struct sched_entity *se)
> >         return delta;
> >  }
> > 
> > -/*
> > - * The idea is to set a period in which each task runs once.
> > - *
> > - * When there are too many tasks (sched_nr_latency) we have to
> > stretch
> > - * this period because otherwise the slices get too small.
> > - *
> > - * p = (nr <= nl) ? l : l*nr/nl
> > - */
> > -static u64 __sched_period(unsigned long nr_running)
> > -{
> > -       if (unlikely(nr_running > sched_nr_latency))
> > -               return nr_running * sysctl_sched_min_granularity;
> > -       else
> > -               return sysctl_sched_latency;
> > -}
> > -
> >  /*
> >   * We calculate the wall-time slice from the period by taking a
> > part
> >   * proportional to the weight.
> > @@ -695,7 +679,7 @@ static u64 __sched_period(unsigned long
> > nr_running)
> >   */
> >  static u64 sched_slice(struct cfs_rq *cfs_rq, struct sched_entity
> > *se)
> >  {
> > -       u64 slice = __sched_period(cfs_rq->nr_running + !se-
> > >on_rq);
> > +       u64 slice = sysctl_sched_latency;
> 
> Is the change above and the remove of __sched_period() really needed
> for fixing the null time slice problem ?
> This change impacts how tasks will preempt each other and as a result
> the throughput. It should have it dedicated patch so we can evaluate
> its impact

Good point. I will split this up into two patches for v3.

Thank you.

-- 
All Rights Reversed.

[-- Attachment #2: This is a digitally signed message part --]
[-- Type: application/pgp-signature, Size: 488 bytes --]