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Subject[RFC PATCH 05/16] sched: Basic tracking of matching tasks
Date
From: Peter Zijlstra <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>
---
include/linux/sched.h | 8 ++-
kernel/sched/core.c | 146 ++++++++++++++++++++++++++++++++++++++++++
kernel/sched/fair.c | 46 -------------
kernel/sched/sched.h | 55 ++++++++++++++++
4 files changed, 208 insertions(+), 47 deletions(-)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 4418f5cb8324..3c8dcc5ff039 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -683,10 +683,16 @@ 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_UCLAMP_TASK
/* Clamp values requested for a scheduling entity */
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 4b81301e3f21..b21bcab20da6 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -77,6 +77,141 @@ 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 */
+}
+
+/*
+ * 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)
+{
+
+ 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);
+
+ if (pa == MAX_RT_PRIO + MAX_NICE) { /* fair */
+ u64 vruntime = b->se.vruntime;
+
+ /*
+ * Normalize the vruntime if tasks are in different cpus.
+ */
+ if (task_cpu(a) != task_cpu(b)) {
+ vruntime -= task_cfs_rq(b)->min_vruntime;
+ vruntime += task_cfs_rq(a)->min_vruntime;
+ }
+
+ return !((s64)(a->se.vruntime - vruntime) <= 0);
+ }
+
+ return false;
+}
+
+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 (prio_less(b, a))
+ return true;
+
+ return false;
+}
+
+static 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);
+}
+
+static 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.
+ */
+static 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 (cookie < node_task->core_cookie) {
+ node = node->rb_left;
+ } else if (cookie > node_task->core_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:
*
@@ -135,6 +270,11 @@ 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 */

/*
@@ -1347,6 +1487,9 @@ static inline void init_uclamp(void) { }

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);

@@ -1361,6 +1504,9 @@ 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/fair.c b/kernel/sched/fair.c
index e44a43b87975..ae17507533a0 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -260,33 +260,11 @@ const struct sched_class fair_sched_class;
*/

#ifdef CONFIG_FAIR_GROUP_SCHED
-static inline struct task_struct *task_of(struct sched_entity *se)
-{
- SCHED_WARN_ON(!entity_is_task(se));
- return container_of(se, struct task_struct, se);
-}

/* Walk up scheduling entities hierarchy */
#define for_each_sched_entity(se) \
for (; se; se = se->parent)

-static inline struct cfs_rq *task_cfs_rq(struct task_struct *p)
-{
- return p->se.cfs_rq;
-}
-
-/* runqueue on which this entity is (to be) queued */
-static inline struct cfs_rq *cfs_rq_of(struct sched_entity *se)
-{
- return se->cfs_rq;
-}
-
-/* runqueue "owned" by this group */
-static inline struct cfs_rq *group_cfs_rq(struct sched_entity *grp)
-{
- return grp->my_q;
-}
-
static inline void cfs_rq_tg_path(struct cfs_rq *cfs_rq, char *path, int len)
{
if (!path)
@@ -447,33 +425,9 @@ find_matching_se(struct sched_entity **se, struct sched_entity **pse)

#else /* !CONFIG_FAIR_GROUP_SCHED */

-static inline struct task_struct *task_of(struct sched_entity *se)
-{
- return container_of(se, struct task_struct, se);
-}
-
#define for_each_sched_entity(se) \
for (; se; se = NULL)

-static inline struct cfs_rq *task_cfs_rq(struct task_struct *p)
-{
- return &task_rq(p)->cfs;
-}
-
-static inline struct cfs_rq *cfs_rq_of(struct sched_entity *se)
-{
- struct task_struct *p = task_of(se);
- struct rq *rq = task_rq(p);
-
- return &rq->cfs;
-}
-
-/* runqueue "owned" by this group */
-static inline struct cfs_rq *group_cfs_rq(struct sched_entity *grp)
-{
- return NULL;
-}
-
static inline void cfs_rq_tg_path(struct cfs_rq *cfs_rq, char *path, int len)
{
if (path)
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 66e586adee18..c85c5a4bc21f 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -1033,6 +1033,10 @@ struct rq {
/* per rq */
struct rq *core;
unsigned int core_enabled;
+ struct rb_root core_tree;
+
+ /* shared state */
+ unsigned int core_task_seq;
#endif
};

@@ -1112,6 +1116,57 @@ DECLARE_PER_CPU_SHARED_ALIGNED(struct rq, runqueues);
#define cpu_curr(cpu) (cpu_rq(cpu)->curr)
#define raw_rq() raw_cpu_ptr(&runqueues)

+#ifdef CONFIG_FAIR_GROUP_SCHED
+static inline struct task_struct *task_of(struct sched_entity *se)
+{
+ SCHED_WARN_ON(!entity_is_task(se));
+ return container_of(se, struct task_struct, se);
+}
+
+static inline struct cfs_rq *task_cfs_rq(struct task_struct *p)
+{
+ return p->se.cfs_rq;
+}
+
+/* runqueue on which this entity is (to be) queued */
+static inline struct cfs_rq *cfs_rq_of(struct sched_entity *se)
+{
+ return se->cfs_rq;
+}
+
+/* runqueue "owned" by this group */
+static inline struct cfs_rq *group_cfs_rq(struct sched_entity *grp)
+{
+ return grp->my_q;
+}
+
+#else
+
+static inline struct task_struct *task_of(struct sched_entity *se)
+{
+ return container_of(se, struct task_struct, se);
+}
+
+static inline struct cfs_rq *task_cfs_rq(struct task_struct *p)
+{
+ return &task_rq(p)->cfs;
+}
+
+static inline struct cfs_rq *cfs_rq_of(struct sched_entity *se)
+{
+ struct task_struct *p = task_of(se);
+ struct rq *rq = task_rq(p);
+
+ return &rq->cfs;
+}
+
+/* runqueue "owned" by this group */
+static inline struct cfs_rq *group_cfs_rq(struct sched_entity *grp)
+{
+ return NULL;
+}
+#endif
+
extern void update_rq_clock(struct rq *rq);

static inline u64 __rq_clock_broken(struct rq *rq)
--
2.17.1
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