[PATCH] drm/sced: Add FIFO policy for scheduler rq

[Andrey Grodzovsky]

Poblem: Given many entities competing for same rq on
same scheduler an uncceptabliy long wait time for some
jobs waiting stuck in rq before being picked up are
observed (seen using  GPUVis).
The issue is due to Round Robin policy used by scheduler
to pick up the next entity for execution. Under stress
of many entities and long job queus within entity some
jobs could be stack for very long time in it's entity's
queue before being popped from the queue and executed
while for other entites with samller job queues a job
might execute ealier even though that job arrived later
then the job in the long queue.

Fix:
Add FIFO selection policy to entites in RQ, chose next enitity
on rq in such order that if job on one entity arrived
ealrier then job on another entity the first job will start
executing ealier regardless of the length of the entity's job
queue.

Signed-off-by: Andrey Grodzovsky <andrey.grodzovsky at amd.com>
Tested-by: Li Yunxiang (Teddy) <Yunxiang.Li at amd.com>
---
 drivers/gpu/drm/scheduler/sched_entity.c |  2 +
 drivers/gpu/drm/scheduler/sched_main.c   | 65 ++++++++++++++++++++++--
 include/drm/gpu_scheduler.h              |  8 +++
 3 files changed, 71 insertions(+), 4 deletions(-)

diff --git a/drivers/gpu/drm/scheduler/sched_entity.c b/drivers/gpu/drm/scheduler/sched_entity.c
index 6b25b2f4f5a3..3bb7f69306ef 100644
--- a/drivers/gpu/drm/scheduler/sched_entity.c
+++ b/drivers/gpu/drm/scheduler/sched_entity.c
@@ -507,6 +507,8 @@ void drm_sched_entity_push_job(struct drm_sched_job *sched_job)
 	atomic_inc(entity->rq->sched->score);
 	WRITE_ONCE(entity->last_user, current->group_leader);
 	first = spsc_queue_push(&entity->job_queue, &sched_job->queue_node);
+	sched_job->submit_ts = ktime_get();
+
 
 	/* first job wakes up scheduler */
 	if (first) {
diff --git a/drivers/gpu/drm/scheduler/sched_main.c b/drivers/gpu/drm/scheduler/sched_main.c
index 68317d3a7a27..c123aa120d06 100644
--- a/drivers/gpu/drm/scheduler/sched_main.c
+++ b/drivers/gpu/drm/scheduler/sched_main.c
@@ -59,6 +59,19 @@
 #define CREATE_TRACE_POINTS
 #include "gpu_scheduler_trace.h"
 
+
+
+int drm_sched_policy = -1;
+
+/**
+ * DOC: sched_policy (int)
+ * Used to override default entites scheduling policy in a run queue.
+ */
+MODULE_PARM_DESC(sched_policy,
+		"specify schedule policy for entites on a runqueue (-1 = auto(default) value, 0 = Round Robin,1  = use FIFO");
+module_param_named(sched_policy, drm_sched_policy, int, 0444);
+
+
 #define to_drm_sched_job(sched_job)		\
 		container_of((sched_job), struct drm_sched_job, queue_node)
 
@@ -120,14 +133,16 @@ void drm_sched_rq_remove_entity(struct drm_sched_rq *rq,
 }
 
 /**
- * drm_sched_rq_select_entity - Select an entity which could provide a job to run
+ * drm_sched_rq_select_entity_rr - Select an entity which could provide a job to run
  *
  * @rq: scheduler run queue to check.
  *
- * Try to find a ready entity, returns NULL if none found.
+ * Try to find a ready entity, in round robin manner.
+ *
+ * Returns NULL if none found.
  */
 static struct drm_sched_entity *
-drm_sched_rq_select_entity(struct drm_sched_rq *rq)
+drm_sched_rq_select_entity_rr(struct drm_sched_rq *rq)
 {
 	struct drm_sched_entity *entity;
 
@@ -163,6 +178,45 @@ drm_sched_rq_select_entity(struct drm_sched_rq *rq)
 	return NULL;
 }
 
+/**
+ * drm_sched_rq_select_entity_fifo - Select an entity which could provide a job to run
+ *
+ * @rq: scheduler run queue to check.
+ *
+ * Try to find a ready entity, based on FIFO order of jobs arrivals.
+ *
+ * Returns NULL if none found.
+ */
+static struct drm_sched_entity *
+drm_sched_rq_select_entity_fifo(struct drm_sched_rq *rq)
+{
+	struct drm_sched_entity *tmp, *entity = NULL;
+	ktime_t oldest_ts = KTIME_MAX;
+	struct drm_sched_job *sched_job;
+
+	spin_lock(&rq->lock);
+
+	list_for_each_entry(tmp, &rq->entities, list) {
+
+		if (drm_sched_entity_is_ready(tmp)) {
+			sched_job = to_drm_sched_job(spsc_queue_peek(&tmp->job_queue));
+
+			if (ktime_before(sched_job->submit_ts, oldest_ts)) {
+				oldest_ts = sched_job->submit_ts;
+				entity = tmp;
+			}
+		}
+	}
+
+	if (entity) {
+		rq->current_entity = entity;
+		reinit_completion(&entity->entity_idle);
+	}
+
+	spin_unlock(&rq->lock);
+	return entity;
+}
+
 /**
  * drm_sched_job_done - complete a job
  * @s_job: pointer to the job which is done
@@ -804,7 +858,10 @@ drm_sched_select_entity(struct drm_gpu_scheduler *sched)
 
 	/* Kernel run queue has higher priority than normal run queue*/
 	for (i = DRM_SCHED_PRIORITY_COUNT - 1; i >= DRM_SCHED_PRIORITY_MIN; i--) {
-		entity = drm_sched_rq_select_entity(&sched->sched_rq[i]);
+		entity = drm_sched_policy != 1 ?
+				drm_sched_rq_select_entity_rr(&sched->sched_rq[i]) :
+				drm_sched_rq_select_entity_fifo(&sched->sched_rq[i]);
+
 		if (entity)
 			break;
 	}
diff --git a/include/drm/gpu_scheduler.h b/include/drm/gpu_scheduler.h
index addb135eeea6..95865881bfcf 100644
--- a/include/drm/gpu_scheduler.h
+++ b/include/drm/gpu_scheduler.h
@@ -314,6 +314,14 @@ struct drm_sched_job {
 
 	/** @last_dependency: tracks @dependencies as they signal */
 	unsigned long			last_dependency;
+
+       /**
+	* @submit_ts:
+	*
+	* Marks job submit time
+	*/
+       ktime_t				submit_ts;
+
 };
 
 static inline bool drm_sched_invalidate_job(struct drm_sched_job *s_job,
-- 
2.25.1