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Subject[tip: sched/core] sched: Basic tracking of matching tasks
The following commit has been merged into the sched/core branch of tip:

Commit-ID: 8a311c740b53324ec584e0e3bb7077d56b123c28
Gitweb: https://git.kernel.org/tip/8a311c740b53324ec584e0e3bb7077d56b123c28
Author: Peter Zijlstra <peterz@infradead.org>
AuthorDate: Tue, 17 Nov 2020 18:19:36 -05:00
Committer: Peter Zijlstra <peterz@infradead.org>
CommitterDate: Wed, 12 May 2021 11:43:28 +02:00

sched: Basic tracking of matching tasks

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).

[Joel: folded fixes]
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Tested-by: Don Hiatt <dhiatt@digitalocean.com>
Tested-by: Hongyu Ning <hongyu.ning@linux.intel.com>
Tested-by: Vincent Guittot <vincent.guittot@linaro.org>
Link: https://lkml.kernel.org/r/20210422123308.496975854@infradead.org
---
include/linux/sched.h | 8 +-
kernel/sched/core.c | 152 +++++++++++++++++++++++++++++++++++++++--
kernel/sched/fair.c | 46 +------------
kernel/sched/sched.h | 55 +++++++++++++++-
4 files changed, 210 insertions(+), 51 deletions(-)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index d2c8813..45eedcc 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -700,10 +700,16 @@ 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
/*
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 85147be..c057d47 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -88,6 +88,133 @@ __read_mostly int scheduler_running;

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;
+}
+
+#define __node_2_sc(node) rb_entry((node), struct task_struct, core_node)
+
+static inline bool rb_sched_core_less(struct rb_node *a, const struct rb_node *b)
+{
+ return __sched_core_less(__node_2_sc(a), __node_2_sc(b));
+}
+
+static inline int rb_sched_core_cmp(const void *key, const struct rb_node *node)
+{
+ const struct task_struct *p = __node_2_sc(node);
+ unsigned long cookie = (unsigned long)key;
+
+ if (cookie < p->core_cookie)
+ return -1;
+
+ if (cookie > p->core_cookie)
+ return 1;
+
+ return 0;
+}
+
+static void sched_core_enqueue(struct rq *rq, struct task_struct *p)
+{
+ rq->core->core_task_seq++;
+
+ if (!p->core_cookie)
+ return;
+
+ rb_add(&p->core_node, &rq->core_tree, rb_sched_core_less);
+}
+
+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;
+
+ node = rb_find_first((void *)cookie, &rq->core_tree, rb_sched_core_cmp);
+ /*
+ * The idle task always matches any cookie!
+ */
+ if (!node)
+ return idle_sched_class.pick_task(rq);
+
+ return __node_2_sc(node);
+}
+
/*
* Magic required such that:
*
@@ -147,10 +274,16 @@ static void __sched_core_flip(bool enabled)
cpus_read_unlock();
}

-static void __sched_core_enable(void)
+static void sched_core_assert_empty(void)
{
- // XXX verify there are no cookie tasks (yet)
+ int cpu;

+ for_each_possible_cpu(cpu)
+ WARN_ON_ONCE(!RB_EMPTY_ROOT(&cpu_rq(cpu)->core_tree));
+}
+
+static void __sched_core_enable(void)
+{
static_branch_enable(&__sched_core_enabled);
/*
* Ensure all previous instances of raw_spin_rq_*lock() have finished
@@ -158,12 +291,12 @@ static void __sched_core_enable(void)
*/
synchronize_rcu();
__sched_core_flip(true);
+ sched_core_assert_empty();
}

static void __sched_core_disable(void)
{
- // XXX verify there are no cookie tasks (left)
-
+ sched_core_assert_empty();
__sched_core_flip(false);
static_branch_disable(&__sched_core_enabled);
}
@@ -205,6 +338,11 @@ void sched_core_put(void)
schedule_work(&_work);
}

+#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 */

/*
@@ -1797,10 +1935,16 @@ static inline void enqueue_task(struct rq *rq, struct task_struct *p, int flags)

uclamp_rq_inc(rq, p);
p->sched_class->enqueue_task(rq, p, flags);
+
+ if (sched_core_enabled(rq))
+ sched_core_enqueue(rq, p);
}

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 51d72ab..08be7a2 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -268,33 +268,11 @@ 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)
@@ -455,33 +433,9 @@ 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 fa990cd..e43a217 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -1080,6 +1080,10 @@ struct rq {
/* per rq */
struct rq *core;
unsigned int core_enabled;
+ struct rb_root core_tree;
+
+ /* shared state */
+ unsigned int core_task_seq;
#endif
};

@@ -1243,6 +1247,57 @@ 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)
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