[PATCH v2] sched/core: Optimize the process of picking the max prio task for the core
From: Cruz Zhao
Date: Sun Oct 02 2022 - 23:24:40 EST
When we pick the max prio task for the core in the case of
sched_core_enabled(), if there's a task with a higher prio sched
class in the runqueue of a SMT, it's not necessary for other SMTs
to traverse lower prio sched classes. So we can change the traversal
order: for each sched class, if there exists a max prio task among
the core, pick it and break the loop.
To compare the prio of the tasks with the same sched class, we
introduce sched_class::prio_less().
Signed-off-by: Cruz Zhao <CruzZhao@xxxxxxxxxxxxxxxxx>
Reported-by: kernel test robot <lkp@xxxxxxxxx>
---
Changes since v1:
Fixes the compile error.
---
kernel/sched/core.c | 33 ++++++++++++++++++++++-----------
kernel/sched/deadline.c | 11 +++++++++++
kernel/sched/fair.c | 5 ++++-
kernel/sched/idle.c | 10 ++++++++++
kernel/sched/rt.c | 10 ++++++++++
kernel/sched/sched.h | 5 +++--
kernel/sched/stop_task.c | 10 ++++++++++
7 files changed, 70 insertions(+), 14 deletions(-)
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index a2d8a1f..50e28c8 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -189,7 +189,7 @@ static inline bool prio_less(struct task_struct *a, struct task_struct *b, bool
return !dl_time_before(a->dl.deadline, b->dl.deadline);
if (pa == MAX_RT_PRIO + MAX_NICE) /* fair */
- return cfs_prio_less(a, b, in_fi);
+ return fair_sched_class.prio_less(a, b, in_fi);
return false;
}
@@ -5886,6 +5886,7 @@ static inline struct task_struct *pick_task(struct rq *rq)
int i, cpu, occ = 0;
struct rq *rq_i;
bool need_sync;
+ struct sched_class *class;
if (!sched_core_enabled(rq))
return __pick_next_task(rq, prev, rf);
@@ -5978,12 +5979,6 @@ static inline struct task_struct *pick_task(struct rq *rq)
}
}
- /*
- * For each thread: do the regular task pick and find the max prio task
- * amongst them.
- *
- * Tie-break prio towards the current CPU
- */
for_each_cpu_wrap(i, smt_mask, cpu) {
rq_i = cpu_rq(i);
@@ -5994,12 +5989,28 @@ static inline struct task_struct *pick_task(struct rq *rq)
*/
if (i != cpu && (rq_i != rq->core || !core_clock_updated))
update_rq_clock(rq_i);
+ }
- p = rq_i->core_pick = pick_task(rq_i);
- if (!max || prio_less(max, p, fi_before))
- max = p;
+ /*
+ * For each thread: do the regular task pick and find the max prio task
+ * amongst them.
+ *
+ * Tie-break prio towards the current CPU
+ */
+ for_each_class(class) {
+ for_each_cpu_wrap(i, smt_mask, cpu) {
+ rq_i = cpu_rq(i);
+ p = rq_i->core_pick = class->pick_task(rq_i);
+ if (!max || (p && class->prio_less(max, p, fi_before)))
+ max = p;
+ }
+ if (max)
+ break;
}
+ if (!max)
+ BUG();
+
cookie = rq->core->core_cookie = max->core_cookie;
/*
@@ -6010,7 +6021,7 @@ static inline struct task_struct *pick_task(struct rq *rq)
rq_i = cpu_rq(i);
p = rq_i->core_pick;
- if (!cookie_equals(p, cookie)) {
+ if (!p || !cookie_equals(p, cookie)) {
p = NULL;
if (cookie)
p = sched_core_find(rq_i, cookie);
diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
index 86dea6a..8e7aa7d 100644
--- a/kernel/sched/deadline.c
+++ b/kernel/sched/deadline.c
@@ -1942,6 +1942,7 @@ static int balance_dl(struct rq *rq, struct task_struct *p, struct rq_flags *rf)
return sched_stop_runnable(rq) || sched_dl_runnable(rq);
}
+
#endif /* CONFIG_SMP */
/*
@@ -2054,6 +2055,13 @@ static void put_prev_task_dl(struct rq *rq, struct task_struct *p)
enqueue_pushable_dl_task(rq, p);
}
+#ifdef CONFIG_SCHED_CORE
+static bool prio_less_dl(struct task_struct *a, struct task_struct *b, bool in_fi)
+{
+ return !dl_time_before(a->dl.deadline, b->dl.deadline);
+}
+#endif
+
/*
* scheduler tick hitting a task of our scheduling class.
*
@@ -2704,6 +2712,9 @@ static void prio_changed_dl(struct rq *rq, struct task_struct *p,
.pick_next_task = pick_next_task_dl,
.put_prev_task = put_prev_task_dl,
.set_next_task = set_next_task_dl,
+#ifdef CONFIG_SCHED_CORE
+ .prio_less = prio_less_dl,
+#endif
#ifdef CONFIG_SMP
.balance = balance_dl,
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index e4a0b8b..eca2636 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -11516,7 +11516,7 @@ void task_vruntime_update(struct rq *rq, struct task_struct *p, bool in_fi)
se_fi_update(se, rq->core->core_forceidle_seq, in_fi);
}
-bool cfs_prio_less(struct task_struct *a, struct task_struct *b, bool in_fi)
+static bool prio_less_fair(struct task_struct *a, struct task_struct *b, bool in_fi)
{
struct rq *rq = task_rq(a);
struct sched_entity *sea = &a->se;
@@ -12159,6 +12159,9 @@ static unsigned int get_rr_interval_fair(struct rq *rq, struct task_struct *task
.pick_next_task = __pick_next_task_fair,
.put_prev_task = put_prev_task_fair,
.set_next_task = set_next_task_fair,
+#ifdef CONFIG_SCHED_CORE
+ .prio_less = prio_less_fair,
+#endif
#ifdef CONFIG_SMP
.balance = balance_fair,
diff --git a/kernel/sched/idle.c b/kernel/sched/idle.c
index f26ab26..a3c3e37 100644
--- a/kernel/sched/idle.c
+++ b/kernel/sched/idle.c
@@ -436,6 +436,13 @@ static void set_next_task_idle(struct rq *rq, struct task_struct *next, bool fir
schedstat_inc(rq->sched_goidle);
}
+#ifdef CONFIG_SCHED_CORE
+static bool prio_less_idle(struct task_struct *a, struct task_struct *b, bool in_fi)
+{
+ return false;
+}
+#endif
+
#ifdef CONFIG_SMP
static struct task_struct *pick_task_idle(struct rq *rq)
{
@@ -507,6 +514,9 @@ static void update_curr_idle(struct rq *rq)
.pick_next_task = pick_next_task_idle,
.put_prev_task = put_prev_task_idle,
.set_next_task = set_next_task_idle,
+#ifdef CONFIG_SCHED_CORE
+ .prio_less = prio_less_idle,
+#endif
#ifdef CONFIG_SMP
.balance = balance_idle,
diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
index d869bcf..4459a90 100644
--- a/kernel/sched/rt.c
+++ b/kernel/sched/rt.c
@@ -1838,6 +1838,13 @@ static void put_prev_task_rt(struct rq *rq, struct task_struct *p)
enqueue_pushable_task(rq, p);
}
+static bool prio_less_rt(struct task_struct *a, struct task_struct *b, bool in_fi)
+{
+ int pa = rt_prio(a->prio), pb = rt_prio(b->prio);
+
+ return -pa < -pb;
+}
+
#ifdef CONFIG_SMP
/* Only try algorithms three times */
@@ -2685,6 +2692,9 @@ static unsigned int get_rr_interval_rt(struct rq *rq, struct task_struct *task)
.pick_next_task = pick_next_task_rt,
.put_prev_task = put_prev_task_rt,
.set_next_task = set_next_task_rt,
+#ifdef CONFIG_SCHED_CORE
+ .prio_less = prio_less_rt,
+#endif
#ifdef CONFIG_SMP
.balance = balance_rt,
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 1644242..a7c6d10 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -1218,8 +1218,6 @@ static inline raw_spinlock_t *__rq_lockp(struct rq *rq)
return &rq->__lock;
}
-bool cfs_prio_less(struct task_struct *a, struct task_struct *b, bool fi);
-
/*
* Helpers to check if the CPU's core cookie matches with the task's cookie
* when core scheduling is enabled.
@@ -2155,6 +2153,9 @@ struct sched_class {
void (*put_prev_task)(struct rq *rq, struct task_struct *p);
void (*set_next_task)(struct rq *rq, struct task_struct *p, bool first);
+#ifdef CONFIG_SCHED_CORE
+ bool (*prio_less)(struct task_struct *a, struct task_struct *b, bool in_fi);
+#endif
#ifdef CONFIG_SMP
int (*balance)(struct rq *rq, struct task_struct *prev, struct rq_flags *rf);
diff --git a/kernel/sched/stop_task.c b/kernel/sched/stop_task.c
index 8559059..c9ddaaa 100644
--- a/kernel/sched/stop_task.c
+++ b/kernel/sched/stop_task.c
@@ -84,6 +84,13 @@ static void put_prev_task_stop(struct rq *rq, struct task_struct *prev)
update_current_exec_runtime(curr, now, delta_exec);
}
+#ifdef CONFIG_SCHED_CORE
+static bool prio_less_stop(struct task_struct *a, struct task_struct *b, bool in_fi)
+{
+ return false;
+}
+#endif
+
/*
* scheduler tick hitting a task of our scheduling class.
*
@@ -125,6 +132,9 @@ static void update_curr_stop(struct rq *rq)
.pick_next_task = pick_next_task_stop,
.put_prev_task = put_prev_task_stop,
.set_next_task = set_next_task_stop,
+#ifdef CONFIG_SCHED_CORE
+ .prio_less = prio_less_stop,
+#endif
#ifdef CONFIG_SMP
.balance = balance_stop,
--
1.8.3.1