[Intel-gfx] [PATCH v5 06/20] drm/sched: improve docs around drm_sched_entity

Daniel Vetter
2021-08-05T10:47:46Z

I found a few too many things that are tricky and not documented, so I
started typing.

I found a few more things that looked broken while typing, see the
varios FIXME in drm_sched_entity.

Also some of the usual logics:
- actually include sched_entity.c declarations, that was lost in the
move here: 620e762f9a98 ("drm/scheduler: move entity handling into
separate file")

- Ditch the kerneldoc for internal functions, keep the comments where
they're describing more than what the function name already implies.

- Switch drm_sched_entity to inline docs.

Acked-by: Melissa Wen <mwen@igalia.com>
Reviewed-by: Boris Brezillon <boris.brezillon@collabora.com> (v1)
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Cc: Lucas Stach <l.stach@pengutronix.de>
Cc: David Airlie <airlied@linux.ie>
Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Cc: Maxime Ripard <mripard@kernel.org>
Cc: Thomas Zimmermann <tzimmermann@suse.de>
Cc: "Christian König" <christian.koenig@amd.com>
Cc: Boris Brezillon <boris.brezillon@collabora.com>
Cc: Steven Price <steven.price@arm.com>
Cc: Emma Anholt <emma@anholt.net>
Cc: Lee Jones <lee.jones@linaro.org>
Cc: Andrey Grodzovsky <andrey.grodzovsky@amd.com>
---
Documentation/gpu/drm-mm.rst | 3 +
drivers/gpu/drm/scheduler/sched_entity.c | 85 ++++---------
include/drm/gpu_scheduler.h | 145 ++++++++++++++++++-----
3 files changed, 146 insertions(+), 87 deletions(-)

diff --git a/Documentation/gpu/drm-mm.rst b/Documentation/gpu/drm-mm.rst
index d5a73fa2c9ef..0198fa43d254 100644
--- a/Documentation/gpu/drm-mm.rst
+++ b/Documentation/gpu/drm-mm.rst
@@ -504,3 +504,6 @@ Scheduler Function References

.. kernel-doc:: drivers/gpu/drm/scheduler/sched_main.c
:export:
+
+.. kernel-doc:: drivers/gpu/drm/scheduler/sched_entity.c
+ :export:
diff --git a/drivers/gpu/drm/scheduler/sched_entity.c b/drivers/gpu/drm/scheduler/sched_entity.c
index e4d33db1eb45..27e1573af96e 100644
--- a/drivers/gpu/drm/scheduler/sched_entity.c
+++ b/drivers/gpu/drm/scheduler/sched_entity.c
@@ -45,8 +45,14 @@
* @guilty: atomic_t set to 1 when a job on this queue
* is found to be guilty causing a timeout
*
- * Note: the sched_list should have at least one element to schedule
- * the entity
+ * Note that the &sched_list must have at least one element to schedule the entity.
+ *
+ * For changing @priority later on at runtime see
+ * drm_sched_entity_set_priority(). For changing the set of schedulers
+ * @sched_list at runtime see drm_sched_entity_modify_sched().
+ *
+ * An entity is cleaned up by callind drm_sched_entity_fini(). See also
+ * drm_sched_entity_destroy().
*
* Returns 0 on success or a negative error code on failure.
*/
@@ -92,6 +98,11 @@ EXPORT_SYMBOL(drm_sched_entity_init);
* @sched_list: the list of new drm scheds which will replace
* existing entity->sched_list
* @num_sched_list: number of drm sched in sched_list
+ *
+ * Note that this must be called under the same common lock for @entity as
+ * drm_sched_job_arm() and drm_sched_entity_push_job(), or the driver needs to
+ * guarantee through some other means that this is never called while new jobs
+ * can be pushed to @entity.
*/
void drm_sched_entity_modify_sched(struct drm_sched_entity *entity,
struct drm_gpu_scheduler **sched_list,
@@ -104,13 +115,6 @@ void drm_sched_entity_modify_sched(struct drm_sched_entity *entity,
}
EXPORT_SYMBOL(drm_sched_entity_modify_sched);

-/**
- * drm_sched_entity_is_idle - Check if entity is idle
- *
- * @entity: scheduler entity
- *
- * Returns true if the entity does not have any unscheduled jobs.
- */
static bool drm_sched_entity_is_idle(struct drm_sched_entity *entity)
{
rmb(); /* for list_empty to work without lock */
@@ -123,13 +127,7 @@ static bool drm_sched_entity_is_idle(struct drm_sched_entity *entity)
return false;
}

-/**
- * drm_sched_entity_is_ready - Check if entity is ready
- *
- * @entity: scheduler entity
- *
- * Return true if entity could provide a job.
- */
+/* Return true if entity could provide a job. */
bool drm_sched_entity_is_ready(struct drm_sched_entity *entity)
{
if (spsc_queue_peek(&entity->job_queue) == NULL)
@@ -192,14 +190,7 @@ long drm_sched_entity_flush(struct drm_sched_entity *entity, long timeout)
}
EXPORT_SYMBOL(drm_sched_entity_flush);

-/**
- * drm_sched_entity_kill_jobs_cb - helper for drm_sched_entity_kill_jobs
- *
- * @f: signaled fence
- * @cb: our callback structure
- *
- * Signal the scheduler finished fence when the entity in question is killed.
- */
+/* Signal the scheduler finished fence when the entity in question is killed. */
static void drm_sched_entity_kill_jobs_cb(struct dma_fence *f,
struct dma_fence_cb *cb)
{
@@ -224,14 +215,6 @@ drm_sched_job_dependency(struct drm_sched_job *job,
return NULL;
}

-/**
- * drm_sched_entity_kill_jobs - Make sure all remaining jobs are killed
- *
- * @entity: entity which is cleaned up
- *
- * Makes sure that all remaining jobs in an entity are killed before it is
- * destroyed.
- */
static void drm_sched_entity_kill_jobs(struct drm_sched_entity *entity)
{
struct drm_sched_job *job;
@@ -273,9 +256,11 @@ static void drm_sched_entity_kill_jobs(struct drm_sched_entity *entity)
*
* @entity: scheduler entity
*
- * This should be called after @drm_sched_entity_do_release. It goes over the
- * entity and signals all jobs with an error code if the process was killed.
+ * Cleanups up @entity which has been initialized by drm_sched_entity_init().
*
+ * If there are potentially job still in flight or getting newly queued
+ * drm_sched_entity_flush() must be called first. This function then goes over
+ * the entity and signals all jobs with an error code if the process was killed.
*/
void drm_sched_entity_fini(struct drm_sched_entity *entity)
{
@@ -315,10 +300,10 @@ EXPORT_SYMBOL(drm_sched_entity_fini);

/**
* drm_sched_entity_destroy - Destroy a context entity
- *
* @entity: scheduler entity
*
- * Calls drm_sched_entity_do_release() and drm_sched_entity_cleanup()
+ * Calls drm_sched_entity_flush() and drm_sched_entity_fini() as a
+ * convenience wrapper.
*/
void drm_sched_entity_destroy(struct drm_sched_entity *entity)
{
@@ -327,9 +312,7 @@ void drm_sched_entity_destroy(struct drm_sched_entity *entity)
}
EXPORT_SYMBOL(drm_sched_entity_destroy);

-/*
- * drm_sched_entity_clear_dep - callback to clear the entities dependency
- */
+/* drm_sched_entity_clear_dep - callback to clear the entities dependency */
static void drm_sched_entity_clear_dep(struct dma_fence *f,
struct dma_fence_cb *cb)
{
@@ -371,11 +354,7 @@ void drm_sched_entity_set_priority(struct drm_sched_entity *entity,
}
EXPORT_SYMBOL(drm_sched_entity_set_priority);

-/**
- * drm_sched_entity_add_dependency_cb - add callback for the entities dependency
- *
- * @entity: entity with dependency
- *
+/*
* Add a callback to the current dependency of the entity to wake up the
* scheduler when the entity becomes available.
*/
@@ -423,13 +402,6 @@ static bool drm_sched_entity_add_dependency_cb(struct drm_sched_entity *entity)
return false;
}

-/**
- * drm_sched_entity_pop_job - get a ready to be scheduled job from the entity
- *
- * @entity: entity to get the job from
- *
- * Process all dependencies and try to get one job from the entities queue.
- */
struct drm_sched_job *drm_sched_entity_pop_job(struct drm_sched_entity *entity)
{
struct drm_sched_job *sched_job;
@@ -465,14 +437,6 @@ struct drm_sched_job *drm_sched_entity_pop_job(struct drm_sched_entity *entity)
return sched_job;
}

-/**
- * drm_sched_entity_select_rq - select a new rq for the entity
- *
- * @entity: scheduler entity
- *
- * Check all prerequisites and select a new rq for the entity for load
- * balancing.
- */
void drm_sched_entity_select_rq(struct drm_sched_entity *entity)
{
struct dma_fence *fence;
@@ -520,7 +484,8 @@ void drm_sched_entity_select_rq(struct drm_sched_entity *entity)
*
* Note: To guarantee that the order of insertion to queue matches the job's
* fence sequence number this function should be called with drm_sched_job_arm()
- * under common lock.
+ * under common lock for the struct drm_sched_entity that was set up for
+ * @sched_job in drm_sched_job_init().
*
* Returns 0 for success, negative error code otherwise.
*/
diff --git a/include/drm/gpu_scheduler.h b/include/drm/gpu_scheduler.h
index b72f73b375a2..7f77a455722c 100644
--- a/include/drm/gpu_scheduler.h
+++ b/include/drm/gpu_scheduler.h
@@ -53,56 +53,147 @@ enum drm_sched_priority {
* struct drm_sched_entity - A wrapper around a job queue (typically
* attached to the DRM file_priv).
*
- * @list: used to append this struct to the list of entities in the
- * runqueue.
- * @rq: runqueue on which this entity is currently scheduled.
- * @sched_list: A list of schedulers (drm_gpu_schedulers).
- * Jobs from this entity can be scheduled on any scheduler
- * on this list.
- * @num_sched_list: number of drm_gpu_schedulers in the sched_list.
- * @priority: priority of the entity
- * @rq_lock: lock to modify the runqueue to which this entity belongs.
- * @job_queue: the list of jobs of this entity.
- * @fence_seq: a linearly increasing seqno incremented with each
- * new &drm_sched_fence which is part of the entity.
- * @fence_context: a unique context for all the fences which belong
- * to this entity.
- * The &drm_sched_fence.scheduled uses the
- * fence_context but &drm_sched_fence.finished uses
- * fence_context + 1.
- * @dependency: the dependency fence of the job which is on the top
- * of the job queue.
- * @cb: callback for the dependency fence above.
- * @guilty: points to ctx's guilty.
- * @fini_status: contains the exit status in case the process was signalled.
- * @last_scheduled: points to the finished fence of the last scheduled job.
- * @last_user: last group leader pushing a job into the entity.
- * @stopped: Marks the enity as removed from rq and destined for termination.
- * @entity_idle: Signals when enityt is not in use
- *
* Entities will emit jobs in order to their corresponding hardware
* ring, and the scheduler will alternate between entities based on
* scheduling policy.
*/
struct drm_sched_entity {
+ /**
+ * @list:
+ *
+ * Used to append this struct to the list of entities in the runqueue
+ * @rq under &drm_sched_rq.entities.
+ *
+ * Protected by &drm_sched_rq.lock of @rq.
+ */
struct list_head list;
+
+ /**
+ * @rq:
+ *
+ * Runqueue on which this entity is currently scheduled.
+ *
+ * FIXME: Locking is very unclear for this. Writers are protected by
+ * @rq_lock, but readers are generally lockless and seem to just race
+ * with not even a READ_ONCE.
+ */
struct drm_sched_rq *rq;
+
+ /**
+ * @sched_list:
+ *
+ * A list of schedulers (struct drm_gpu_scheduler). Jobs from this entity can
+ * be scheduled on any scheduler on this list.
+ *
+ * This can be modified by calling drm_sched_entity_modify_sched().
+ * Locking is entirely up to the driver, see the above function for more
+ * details.
+ *
+ * This will be set to NULL if &num_sched_list equals 1 and @rq has been
+ * set already.
+ *
+ * FIXME: This means priority changes through
+ * drm_sched_entity_set_priority() will be lost henceforth in this case.
+ */
struct drm_gpu_scheduler **sched_list;
+
+ /**
+ * @num_sched_list:
+ *
+ * Number of drm_gpu_schedulers in the @sched_list.
+ */
unsigned int num_sched_list;
+
+ /**
+ * @priority:
+ *
+ * Priority of the entity. This can be modified by calling
+ * drm_sched_entity_set_priority(). Protected by &rq_lock.
+ */
enum drm_sched_priority priority;
+
+ /**
+ * @rq_lock:
+ *
+ * Lock to modify the runqueue to which this entity belongs.
+ */
spinlock_t rq_lock;

+ /**
+ * @job_queue: the list of jobs of this entity.
+ */
struct spsc_queue job_queue;

+ /**
+ * @fence_seq:
+ *
+ * A linearly increasing seqno incremented with each new
+ * &drm_sched_fence which is part of the entity.
+ *
+ * FIXME: Callers of drm_sched_job_arm() need to ensure correct locking,
+ * this doesn't need to be atomic.
+ */
atomic_t fence_seq;
+
+ /**
+ * @fence_context:
+ *
+ * A unique context for all the fences which belong to this entity. The
+ * &drm_sched_fence.scheduled uses the fence_context but
+ * &drm_sched_fence.finished uses fence_context + 1.
+ */
uint64_t fence_context;

+ /**
+ * @dependency:
+ *
+ * The dependency fence of the job which is on the top of the job queue.
+ */
struct dma_fence *dependency;
+
+ /**
+ * @cb:
+ *
+ * Callback for the dependency fence above.
+ */
struct dma_fence_cb cb;
+
+ /**
+ * @guilty:
+ *
+ * Points to entities' guilty.
+ */
atomic_t *guilty;
+
+ /**
+ * @last_scheduled:
+ *
+ * Points to the finished fence of the last scheduled job. Only written
+ * by the scheduler thread, can be accessed locklessly from
+ * drm_sched_job_arm() iff the queue is empty.
+ */
struct dma_fence *last_scheduled;
+
+ /**
+ * @last_user: last group leader pushing a job into the entity.
+ */
struct task_struct *last_user;
+
+ /**
+ * @stopped:
+ *
+ * Marks the enity as removed from rq and destined for
+ * termination. This is set by calling drm_sched_entity_flush() and by
+ * drm_sched_fini().
+ */
bool stopped;
+
+ /**
+ * @entity_idle:
+ *
+ * Signals when entity is not in use, used to sequence entity cleanup in
+ * drm_sched_entity_fini().
+ */
struct completion entity_idle;
};

--
2.32.0