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Message-Id: <20230928150251.463109-1-vschneid@redhat.com>
Date: Thu, 28 Sep 2023 17:02:51 +0200
From: Valentin Schneider <vschneid@...hat.com>
To: linux-kernel@...r.kernel.org
Cc: Daniel Bristot de Oliveira <bristot@...hat.com>,
Dietmar Eggemann <dietmar.eggemann@....com>,
Ingo Molnar <mingo@...hat.com>,
Juri Lelli <juri.lelli@...hat.com>,
Peter Zijlstra <peterz@...radead.org>,
Steven Rostedt <rostedt@...dmis.org>,
Vincent Guittot <vincent.guittot@...aro.org>,
Thomas Gleixner <tglx@...utronix.de>,
Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Subject: [PATCH] sched/deadline: Make dl_rq->pushable_dl_tasks updates drive dl_rq->overloaded
dl_nr_migratory is increased whenever a DL entity is enqueued and it has
nr_cpus_allowed > 1. Unlike the pushable_dl_tasks tree, dl_nr_migratory
includes a dl_rq's current task. This means a dl_rq can have a migratable
current, N non-migratable queued tasks, and be flagged as overloaded and have
its CPU set in the dlo_mask, despite having an empty pushable_tasks tree.
Make an dl_rq's overload logic be driven by {enqueue,dequeue}_pushable_dl_task(),
in other words make DL RQs only be flagged as overloaded if they have at
least one runnable-but-not-current migratable task.
o push_dl_task() is unaffected, as it is a no-op if there are no pushable
tasks.
o pull_dl_task() now no longer scans runqueues whose sole migratable task is
their current one, which it can't do anything about anyway.
It may also now pull tasks to a DL RQ with dl_nr_running > 1 if only its
current task is migratable.
Since dl_rq->dl_nr_migratory becomes unused, remove it.
RT had the exact same mechanism (rt_rq->rt_nr_migratory) which was dropped
in favour of relying on rt_rq->pushable_tasks, see:
612f769edd06 ("sched/rt: Make rt_rq->pushable_tasks updates drive rto_mask")
Link: https://lore.kernel.org/all/20230811112044.3302588-1-vschneid@redhat.com/
Signed-off-by: Valentin Schneider <vschneid@...hat.com>
---
kernel/sched/deadline.c | 57 ++++++++++-------------------------------
kernel/sched/debug.c | 1 -
kernel/sched/sched.h | 1 -
3 files changed, 14 insertions(+), 45 deletions(-)
diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
index fb1996a674db5..d98408a274e52 100644
--- a/kernel/sched/deadline.c
+++ b/kernel/sched/deadline.c
@@ -509,7 +509,6 @@ void init_dl_rq(struct dl_rq *dl_rq)
/* zero means no -deadline tasks */
dl_rq->earliest_dl.curr = dl_rq->earliest_dl.next = 0;
- dl_rq->dl_nr_migratory = 0;
dl_rq->overloaded = 0;
dl_rq->pushable_dl_tasks_root = RB_ROOT_CACHED;
#else
@@ -553,39 +552,6 @@ static inline void dl_clear_overload(struct rq *rq)
cpumask_clear_cpu(rq->cpu, rq->rd->dlo_mask);
}
-static void update_dl_migration(struct dl_rq *dl_rq)
-{
- if (dl_rq->dl_nr_migratory && dl_rq->dl_nr_running > 1) {
- if (!dl_rq->overloaded) {
- dl_set_overload(rq_of_dl_rq(dl_rq));
- dl_rq->overloaded = 1;
- }
- } else if (dl_rq->overloaded) {
- dl_clear_overload(rq_of_dl_rq(dl_rq));
- dl_rq->overloaded = 0;
- }
-}
-
-static void inc_dl_migration(struct sched_dl_entity *dl_se, struct dl_rq *dl_rq)
-{
- struct task_struct *p = dl_task_of(dl_se);
-
- if (p->nr_cpus_allowed > 1)
- dl_rq->dl_nr_migratory++;
-
- update_dl_migration(dl_rq);
-}
-
-static void dec_dl_migration(struct sched_dl_entity *dl_se, struct dl_rq *dl_rq)
-{
- struct task_struct *p = dl_task_of(dl_se);
-
- if (p->nr_cpus_allowed > 1)
- dl_rq->dl_nr_migratory--;
-
- update_dl_migration(dl_rq);
-}
-
#define __node_2_pdl(node) \
rb_entry((node), struct task_struct, pushable_dl_tasks)
@@ -594,6 +560,11 @@ static inline bool __pushable_less(struct rb_node *a, const struct rb_node *b)
return dl_entity_preempt(&__node_2_pdl(a)->dl, &__node_2_pdl(b)->dl);
}
+static inline int has_pushable_dl_tasks(struct rq *rq)
+{
+ return !RB_EMPTY_ROOT(&rq->dl.pushable_dl_tasks_root.rb_root);
+}
+
/*
* The list of pushable -deadline task is not a plist, like in
* sched_rt.c, it is an rb-tree with tasks ordered by deadline.
@@ -609,6 +580,11 @@ static void enqueue_pushable_dl_task(struct rq *rq, struct task_struct *p)
__pushable_less);
if (leftmost)
rq->dl.earliest_dl.next = p->dl.deadline;
+
+ if (!rq->dl.overloaded) {
+ dl_set_overload(rq);
+ rq->dl.overloaded = 1;
+ }
}
static void dequeue_pushable_dl_task(struct rq *rq, struct task_struct *p)
@@ -625,11 +601,11 @@ static void dequeue_pushable_dl_task(struct rq *rq, struct task_struct *p)
dl_rq->earliest_dl.next = __node_2_pdl(leftmost)->dl.deadline;
RB_CLEAR_NODE(&p->pushable_dl_tasks);
-}
-static inline int has_pushable_dl_tasks(struct rq *rq)
-{
- return !RB_EMPTY_ROOT(&rq->dl.pushable_dl_tasks_root.rb_root);
+ if (!has_pushable_dl_tasks(rq) && rq->dl.overloaded) {
+ dl_clear_overload(rq);
+ rq->dl.overloaded = 0;
+ }
}
static int push_dl_task(struct rq *rq);
@@ -1504,7 +1480,6 @@ void inc_dl_tasks(struct sched_dl_entity *dl_se, struct dl_rq *dl_rq)
add_nr_running(rq_of_dl_rq(dl_rq), 1);
inc_dl_deadline(dl_rq, deadline);
- inc_dl_migration(dl_se, dl_rq);
}
static inline
@@ -1518,7 +1493,6 @@ void dec_dl_tasks(struct sched_dl_entity *dl_se, struct dl_rq *dl_rq)
sub_nr_running(rq_of_dl_rq(dl_rq), 1);
dec_dl_deadline(dl_rq, dl_se->deadline);
- dec_dl_migration(dl_se, dl_rq);
}
static inline bool __dl_less(struct rb_node *a, const struct rb_node *b)
@@ -2291,9 +2265,6 @@ static int push_dl_task(struct rq *rq)
struct rq *later_rq;
int ret = 0;
- if (!rq->dl.overloaded)
- return 0;
-
next_task = pick_next_pushable_dl_task(rq);
if (!next_task)
return 0;
diff --git a/kernel/sched/debug.c b/kernel/sched/debug.c
index c4253bd2dfb01..4580a450700ec 100644
--- a/kernel/sched/debug.c
+++ b/kernel/sched/debug.c
@@ -745,7 +745,6 @@ void print_dl_rq(struct seq_file *m, int cpu, struct dl_rq *dl_rq)
PU(dl_nr_running);
#ifdef CONFIG_SMP
- PU(dl_nr_migratory);
dl_bw = &cpu_rq(cpu)->rd->dl_bw;
#else
dl_bw = &dl_rq->dl_bw;
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 41d760df458f7..649eb9ec06575 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -707,7 +707,6 @@ struct dl_rq {
u64 next;
} earliest_dl;
- unsigned int dl_nr_migratory;
int overloaded;
/*
--
2.31.1
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