[PATCH v1 1/2] evl/sched: core: introduce schedule out handler

From: Philippe Gerum <[email protected]>

Some scheduling classes may need a way to perform specific
fixup/accounting work for a thread which is being scheduled out.  We
cannot rely on the sched_pick() handler for this since the first one
to successfully pick a thread prevents other handlers down the class
hierarchy to run.

To address this issue, we introduce the sched_out() handler which is
called for the current thread when scheduled out. This handler is
invoked unconditionally when present prior to picking a new thread.

Signed-off-by: Philippe Gerum <[email protected]>
---
 include/evl/sched.h     |  1 +
 kernel/evl/sched/core.c | 20 +++++++++++++-------
 2 files changed, 14 insertions(+), 7 deletions(-)

diff --git a/include/evl/sched.h b/include/evl/sched.h
index ae9690860146..cc824c28004b 100644
--- a/include/evl/sched.h
+++ b/include/evl/sched.h
@@ -120,6 +120,7 @@ struct evl_sched_class {
 	void (*sched_dequeue)(struct evl_thread *thread);
 	void (*sched_requeue)(struct evl_thread *thread);
 	struct evl_thread *(*sched_pick)(struct evl_rq *rq);
+	void (*sched_out)(struct evl_thread *thread);
 	void (*sched_yield)(struct evl_thread *thread);
 	void (*sched_migrate)(struct evl_thread *thread,
 			      struct evl_rq *rq);
diff --git a/kernel/evl/sched/core.c b/kernel/evl/sched/core.c
index d1d025e06a5d..7127d4e52df9 100644
--- a/kernel/evl/sched/core.c
+++ b/kernel/evl/sched/core.c
@@ -773,7 +773,8 @@ static inline void set_next_running(struct evl_rq *rq,
 		evl_stop_timer(&rq->rrbtimer);
 }
 
-static struct evl_thread *__pick_next_thread(struct evl_rq *rq)
+static __always_inline struct evl_thread *
+__pick_next_thread(struct evl_rq *rq)
 {
 	struct evl_sched_class *sched_class;
 	struct evl_thread *curr = rq->curr;
@@ -821,8 +822,14 @@ static struct evl_thread *__pick_next_thread(struct evl_rq *rq)
 /* rq->curr->lock + rq->lock held, hard irqs off. */
 static struct evl_thread *pick_next_thread(struct evl_rq *rq)
 {
-	struct evl_thread *next = __pick_next_thread(rq);
+	struct evl_thread *next, *prev = rq->curr;
+	struct evl_sched_class *prev_class = prev->sched_class;
 
+	if (prev_class->sched_out)
+		prev_class->sched_out(prev);
+
+	next = __pick_next_thread(rq);
+	trace_evl_pick_thread(next);
 	set_next_running(rq, next);
 
 	return next;
@@ -972,21 +979,20 @@ void __evl_schedule(void) /* oob or/and hard irqs off (CPU migration-safe) */
 		return;
 	}
 
+	prev = curr;
 	next = pick_next_thread(this_rq);
-	trace_evl_pick_thread(next);
-	if (next == curr) {
-		if (unlikely(next->state & EVL_T_ROOT)) {
+	if (next == prev) {
+		if (unlikely(prev->state & EVL_T_ROOT)) {
 			if (this_rq->local_flags & RQ_TPROXY)
 				evl_notify_proxy_tick(this_rq);
 			if (this_rq->local_flags & RQ_TDEFER)
 				evl_program_local_tick(&evl_mono_clock);
 		}
 		raw_spin_unlock(&this_rq->lock);
-		raw_spin_unlock_irqrestore(&curr->lock, flags);
+		raw_spin_unlock_irqrestore(&prev->lock, flags);
 		return;
 	}
 
-	prev = curr;
 	this_rq->curr = next;
 	leaving_inband = false;
 
-- 
2.54.0