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Subject[RFC PATCH v2 11/17] sched: Basic tracking of matching tasks
Date
From: Peter Zijlstra (Intel) <peterz@infradead.org>

Introduce task_struct::core_cookie as an opaque identifier for core
scheduling. When enabled; core scheduling will only allow matching
task to be on the core; where idle matches everything.

When task_struct::core_cookie is set (and core scheduling is enabled)
these tasks are indexed in a second RB-tree, first on cookie value
then on scheduling function, such that matching task selection always
finds the most elegible match.

NOTE: *shudder* at the overhead...

NOTE: *sigh*, a 3rd copy of the scheduling function; the alternative
is per class tracking of cookies and that just duplicates a lot of
stuff for no raisin (the 2nd copy lives in the rt-mutex PI code).

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Vineeth Remanan Pillai <vpillai@digitalocean.com>
Signed-off-by: Julien Desfossez <jdesfossez@digitalocean.com>
---

Changes in v2
-------------
- Improves the priority comparison logic between processes in
different cpus.
- Peter Zijlstra
- Aaron Lu

---
include/linux/sched.h | 8 ++-
kernel/sched/core.c | 164 ++++++++++++++++++++++++++++++++++++++++++
kernel/sched/sched.h | 4 ++
3 files changed, 175 insertions(+), 1 deletion(-)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 1549584a1538..a4b39a28236f 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -636,10 +636,16 @@ struct task_struct {
const struct sched_class *sched_class;
struct sched_entity se;
struct sched_rt_entity rt;
+ struct sched_dl_entity dl;
+
+#ifdef CONFIG_SCHED_CORE
+ struct rb_node core_node;
+ unsigned long core_cookie;
+#endif
+
#ifdef CONFIG_CGROUP_SCHED
struct task_group *sched_task_group;
#endif
- struct sched_dl_entity dl;

#ifdef CONFIG_PREEMPT_NOTIFIERS
/* List of struct preempt_notifier: */
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 2f559d706b8e..5066a1493acf 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -64,6 +64,159 @@ int sysctl_sched_rt_runtime = 950000;

DEFINE_STATIC_KEY_FALSE(__sched_core_enabled);

+/* kernel prio, less is more */
+static inline int __task_prio(struct task_struct *p)
+{
+ if (p->sched_class == &stop_sched_class) /* trumps deadline */
+ return -2;
+
+ if (rt_prio(p->prio)) /* includes deadline */
+ return p->prio; /* [-1, 99] */
+
+ if (p->sched_class == &idle_sched_class)
+ return MAX_RT_PRIO + NICE_WIDTH; /* 140 */
+
+ return MAX_RT_PRIO + MAX_NICE; /* 120, squash fair */
+}
+
+// FIXME: This is copied from fair.c. Needs only single copy.
+#ifdef CONFIG_FAIR_GROUP_SCHED
+static inline struct cfs_rq *task_cfs_rq(struct task_struct *p)
+{
+ return p->se.cfs_rq;
+}
+#else
+static inline struct cfs_rq *task_cfs_rq(struct task_struct *p)
+{
+ return &task_rq(p)->cfs;
+}
+#endif
+
+/*
+ * l(a,b)
+ * le(a,b) := !l(b,a)
+ * g(a,b) := l(b,a)
+ * ge(a,b) := !l(a,b)
+ */
+
+/* real prio, less is less */
+static inline bool __prio_less(struct task_struct *a, struct task_struct *b, bool core_cmp)
+{
+ u64 vruntime;
+
+ int pa = __task_prio(a), pb = __task_prio(b);
+
+ if (-pa < -pb)
+ return true;
+
+ if (-pb < -pa)
+ return false;
+
+ if (pa == -1) /* dl_prio() doesn't work because of stop_class above */
+ return !dl_time_before(a->dl.deadline, b->dl.deadline);
+
+ vruntime = b->se.vruntime;
+ if (core_cmp) {
+ vruntime -= task_cfs_rq(b)->min_vruntime;
+ vruntime += task_cfs_rq(a)->min_vruntime;
+ }
+ if (pa == MAX_RT_PRIO + MAX_NICE) /* fair */
+ return !((s64)(a->se.vruntime - vruntime) <= 0);
+
+ return false;
+}
+
+static inline bool cpu_prio_less(struct task_struct *a, struct task_struct *b)
+{
+ return __prio_less(a, b, false);
+}
+
+static inline bool core_prio_less(struct task_struct *a, struct task_struct *b)
+{
+ return __prio_less(a, b, true);
+}
+
+static inline bool __sched_core_less(struct task_struct *a, struct task_struct *b)
+{
+ if (a->core_cookie < b->core_cookie)
+ return true;
+
+ if (a->core_cookie > b->core_cookie)
+ return false;
+
+ /* flip prio, so high prio is leftmost */
+ if (cpu_prio_less(b, a))
+ return true;
+
+ return false;
+}
+
+void sched_core_enqueue(struct rq *rq, struct task_struct *p)
+{
+ struct rb_node *parent, **node;
+ struct task_struct *node_task;
+
+ rq->core->core_task_seq++;
+
+ if (!p->core_cookie)
+ return;
+
+ node = &rq->core_tree.rb_node;
+ parent = *node;
+
+ while (*node) {
+ node_task = container_of(*node, struct task_struct, core_node);
+ parent = *node;
+
+ if (__sched_core_less(p, node_task))
+ node = &parent->rb_left;
+ else
+ node = &parent->rb_right;
+ }
+
+ rb_link_node(&p->core_node, parent, node);
+ rb_insert_color(&p->core_node, &rq->core_tree);
+}
+
+void sched_core_dequeue(struct rq *rq, struct task_struct *p)
+{
+ rq->core->core_task_seq++;
+
+ if (!p->core_cookie)
+ return;
+
+ rb_erase(&p->core_node, &rq->core_tree);
+}
+
+/*
+ * Find left-most (aka, highest priority) task matching @cookie.
+ */
+struct task_struct *sched_core_find(struct rq *rq, unsigned long cookie)
+{
+ struct rb_node *node = rq->core_tree.rb_node;
+ struct task_struct *node_task, *match;
+
+ /*
+ * The idle task always matches any cookie!
+ */
+ match = idle_sched_class.pick_task(rq);
+
+ while (node) {
+ node_task = container_of(node, struct task_struct, core_node);
+
+ if (node_task->core_cookie < cookie) {
+ node = node->rb_left;
+ } else if (node_task->core_cookie > cookie) {
+ node = node->rb_right;
+ } else {
+ match = node_task;
+ node = node->rb_left;
+ }
+ }
+
+ return match;
+}
+
/*
* The static-key + stop-machine variable are needed such that:
*
@@ -122,6 +275,11 @@ void sched_core_put(void)
mutex_unlock(&sched_core_mutex);
}

+#else /* !CONFIG_SCHED_CORE */
+
+static inline void sched_core_enqueue(struct rq *rq, struct task_struct *p) { }
+static inline void sched_core_dequeue(struct rq *rq, struct task_struct *p) { }
+
#endif /* CONFIG_SCHED_CORE */

/*
@@ -826,6 +984,9 @@ static void set_load_weight(struct task_struct *p, bool update_load)

static inline void enqueue_task(struct rq *rq, struct task_struct *p, int flags)
{
+ if (sched_core_enabled(rq))
+ sched_core_enqueue(rq, p);
+
if (!(flags & ENQUEUE_NOCLOCK))
update_rq_clock(rq);

@@ -839,6 +1000,9 @@ static inline void enqueue_task(struct rq *rq, struct task_struct *p, int flags)

static inline void dequeue_task(struct rq *rq, struct task_struct *p, int flags)
{
+ if (sched_core_enabled(rq))
+ sched_core_dequeue(rq, p);
+
if (!(flags & DEQUEUE_NOCLOCK))
update_rq_clock(rq);

diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index eb38063221d0..42dd620797d7 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -957,6 +957,10 @@ struct rq {
/* per rq */
struct rq *core;
unsigned int core_enabled;
+ struct rb_root core_tree;
+
+ /* shared state */
+ unsigned int core_task_seq;
#endif
};

--
2.17.1
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