drm/sched: Add scheduler unit testing infrastructure and some basic tests

Implement a mock scheduler backend and add some basic test to exercise the
core scheduler code paths.

Mock backend (kind of like a very simple mock GPU) can either process jobs
by tests manually advancing the "timeline" job at a time, or alternatively
jobs can be configured with a time duration in which case they get
completed asynchronously from the unit test code.

Core scheduler classes are subclassed to support this mock implementation.

The tests added are just a few simple submission patterns.

Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@igalia.com>
Suggested-by: Philipp Stanner <phasta@kernel.org>
Cc: Christian König <christian.koenig@amd.com>
Cc: Danilo Krummrich <dakr@kernel.org>
Cc: Matthew Brost <matthew.brost@intel.com>
Cc: Philipp Stanner <phasta@kernel.org>
Acked-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Philipp Stanner <phasta@kernel.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20250324092633.49746-3-tvrtko.ursulin@igalia.com

drivers/gpu/drm/scheduler/tests/mock_scheduler.c

@@ -0,0 +1,354 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2025 Valve Corporation */
+
+#include "sched_tests.h"
+
+/*
+ * Here we implement the mock "GPU" (or the scheduler backend) which is used by
+ * the DRM scheduler unit tests in order to exercise the core functionality.
+ *
+ * Test cases are implemented in a separate file.
+ */
+
+/**
+ * drm_mock_sched_entity_new - Create a new mock scheduler entity
+ *
+ * @test: KUnit test owning the entity
+ * @priority: Scheduling priority
+ * @sched: Mock scheduler on which the entity can be scheduled
+ *
+ * Returns: New mock scheduler entity with allocation managed by the test
+ */
+struct drm_mock_sched_entity *
+drm_mock_sched_entity_new(struct kunit *test,
+			  enum drm_sched_priority priority,
+			  struct drm_mock_scheduler *sched)
+{
+	struct drm_mock_sched_entity *entity;
+	struct drm_gpu_scheduler *drm_sched;
+	int ret;
+
+	entity = kunit_kzalloc(test, sizeof(*entity), GFP_KERNEL);
+	KUNIT_ASSERT_NOT_NULL(test, entity);
+
+	drm_sched = &sched->base;
+	ret = drm_sched_entity_init(&entity->base,
+				    priority,
+				    &drm_sched, 1,
+				    NULL);
+	KUNIT_ASSERT_EQ(test, ret, 0);
+
+	entity->test = test;
+
+	return entity;
+}
+
+/**
+ * drm_mock_sched_entity_free - Destroys a mock scheduler entity
+ *
+ * @entity: Entity to destroy
+ *
+ * To be used from the test cases once done with the entity.
+ */
+void drm_mock_sched_entity_free(struct drm_mock_sched_entity *entity)
+{
+	drm_sched_entity_destroy(&entity->base);
+}
+
+static void drm_mock_sched_job_complete(struct drm_mock_sched_job *job)
+{
+	struct drm_mock_scheduler *sched =
+		drm_sched_to_mock_sched(job->base.sched);
+
+	lockdep_assert_held(&sched->lock);
+
+	job->flags |= DRM_MOCK_SCHED_JOB_DONE;
+	list_move_tail(&job->link, &sched->done_list);
+	dma_fence_signal(&job->hw_fence);
+	complete(&job->done);
+}
+
+static enum hrtimer_restart
+drm_mock_sched_job_signal_timer(struct hrtimer *hrtimer)
+{
+	struct drm_mock_sched_job *job =
+		container_of(hrtimer, typeof(*job), timer);
+	struct drm_mock_scheduler *sched =
+		drm_sched_to_mock_sched(job->base.sched);
+	struct drm_mock_sched_job *next;
+	ktime_t now = ktime_get();
+	unsigned long flags;
+	LIST_HEAD(signal);
+
+	spin_lock_irqsave(&sched->lock, flags);
+	list_for_each_entry_safe(job, next, &sched->job_list, link) {
+		if (!job->duration_us)
+			break;
+
+		if (ktime_before(now, job->finish_at))
+			break;
+
+		sched->hw_timeline.cur_seqno = job->hw_fence.seqno;
+		drm_mock_sched_job_complete(job);
+	}
+	spin_unlock_irqrestore(&sched->lock, flags);
+
+	return HRTIMER_NORESTART;
+}
+
+/**
+ * drm_mock_sched_job_new - Create a new mock scheduler job
+ *
+ * @test: KUnit test owning the job
+ * @entity: Scheduler entity of the job
+ *
+ * Returns: New mock scheduler job with allocation managed by the test
+ */
+struct drm_mock_sched_job *
+drm_mock_sched_job_new(struct kunit *test,
+		       struct drm_mock_sched_entity *entity)
+{
+	struct drm_mock_sched_job *job;
+	int ret;
+
+	job = kunit_kzalloc(test, sizeof(*job), GFP_KERNEL);
+	KUNIT_ASSERT_NOT_NULL(test, job);
+
+	ret = drm_sched_job_init(&job->base,
+				 &entity->base,
+				 1,
+				 NULL);
+	KUNIT_ASSERT_EQ(test, ret, 0);
+
+	job->test = test;
+
+	init_completion(&job->done);
+	spin_lock_init(&job->lock);
+	INIT_LIST_HEAD(&job->link);
+	hrtimer_init(&job->timer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS);
+	job->timer.function = drm_mock_sched_job_signal_timer;
+
+	return job;
+}
+
+static const char *drm_mock_sched_hw_fence_driver_name(struct dma_fence *fence)
+{
+	return "drm_mock_sched";
+}
+
+static const char *
+drm_mock_sched_hw_fence_timeline_name(struct dma_fence *fence)
+{
+	struct drm_mock_sched_job *job =
+		container_of(fence, typeof(*job), hw_fence);
+
+	return (const char *)job->base.sched->name;
+}
+
+static void drm_mock_sched_hw_fence_release(struct dma_fence *fence)
+{
+	struct drm_mock_sched_job *job =
+		container_of(fence, typeof(*job), hw_fence);
+
+	hrtimer_cancel(&job->timer);
+
+	/* Containing job is freed by the kunit framework */
+}
+
+static const struct dma_fence_ops drm_mock_sched_hw_fence_ops = {
+	.get_driver_name = drm_mock_sched_hw_fence_driver_name,
+	.get_timeline_name = drm_mock_sched_hw_fence_timeline_name,
+	.release = drm_mock_sched_hw_fence_release,
+};
+
+static struct dma_fence *mock_sched_run_job(struct drm_sched_job *sched_job)
+{
+	struct drm_mock_scheduler *sched =
+		drm_sched_to_mock_sched(sched_job->sched);
+	struct drm_mock_sched_job *job = drm_sched_job_to_mock_job(sched_job);
+
+	dma_fence_init(&job->hw_fence,
+		       &drm_mock_sched_hw_fence_ops,
+		       &job->lock,
+		       sched->hw_timeline.context,
+		       atomic_inc_return(&sched->hw_timeline.next_seqno));
+
+	dma_fence_get(&job->hw_fence); /* Reference for the job_list */
+
+	spin_lock_irq(&sched->lock);
+	if (job->duration_us) {
+		ktime_t prev_finish_at = 0;
+
+		if (!list_empty(&sched->job_list)) {
+			struct drm_mock_sched_job *prev =
+				list_last_entry(&sched->job_list, typeof(*prev),
+						link);
+
+			prev_finish_at = prev->finish_at;
+		}
+
+		if (!prev_finish_at)
+			prev_finish_at = ktime_get();
+
+		job->finish_at = ktime_add_us(prev_finish_at, job->duration_us);
+	}
+	list_add_tail(&job->link, &sched->job_list);
+	if (job->finish_at)
+		hrtimer_start(&job->timer, job->finish_at, HRTIMER_MODE_ABS);
+	spin_unlock_irq(&sched->lock);
+
+	return &job->hw_fence;
+}
+
+static enum drm_gpu_sched_stat
+mock_sched_timedout_job(struct drm_sched_job *sched_job)
+{
+	return DRM_GPU_SCHED_STAT_ENODEV;
+}
+
+static void mock_sched_free_job(struct drm_sched_job *sched_job)
+{
+	struct drm_mock_scheduler *sched =
+			drm_sched_to_mock_sched(sched_job->sched);
+	struct drm_mock_sched_job *job = drm_sched_job_to_mock_job(sched_job);
+	unsigned long flags;
+
+	/* Remove from the scheduler done list. */
+	spin_lock_irqsave(&sched->lock, flags);
+	list_del(&job->link);
+	spin_unlock_irqrestore(&sched->lock, flags);
+	dma_fence_put(&job->hw_fence);
+
+	drm_sched_job_cleanup(sched_job);
+
+	/* Mock job itself is freed by the kunit framework. */
+}
+
+static const struct drm_sched_backend_ops drm_mock_scheduler_ops = {
+	.run_job = mock_sched_run_job,
+	.timedout_job = mock_sched_timedout_job,
+	.free_job = mock_sched_free_job
+};
+
+/**
+ * drm_mock_sched_new - Create a new mock scheduler
+ *
+ * @test: KUnit test owning the job
+ *
+ * Returns: New mock scheduler with allocation managed by the test
+ */
+struct drm_mock_scheduler *drm_mock_sched_new(struct kunit *test)
+{
+	struct drm_sched_init_args args = {
+		.ops		= &drm_mock_scheduler_ops,
+		.num_rqs	= DRM_SCHED_PRIORITY_COUNT,
+		.credit_limit	= U32_MAX,
+		.hang_limit	= 1,
+		.timeout	= MAX_SCHEDULE_TIMEOUT,
+		.name		= "drm-mock-scheduler",
+	};
+	struct drm_mock_scheduler *sched;
+	int ret;
+
+	sched = kunit_kzalloc(test, sizeof(*sched), GFP_KERNEL);
+	KUNIT_ASSERT_NOT_NULL(test, sched);
+
+	ret = drm_sched_init(&sched->base, &args);
+	KUNIT_ASSERT_EQ(test, ret, 0);
+
+	sched->test = test;
+	sched->hw_timeline.context = dma_fence_context_alloc(1);
+	atomic_set(&sched->hw_timeline.next_seqno, 0);
+	INIT_LIST_HEAD(&sched->job_list);
+	INIT_LIST_HEAD(&sched->done_list);
+	spin_lock_init(&sched->lock);
+
+	return sched;
+}
+
+/**
+ * drm_mock_sched_fini - Destroys a mock scheduler
+ *
+ * @sched: Scheduler to destroy
+ *
+ * To be used from the test cases once done with the scheduler.
+ */
+void drm_mock_sched_fini(struct drm_mock_scheduler *sched)
+{
+	struct drm_mock_sched_job *job, *next;
+	unsigned long flags;
+	LIST_HEAD(list);
+
+	drm_sched_wqueue_stop(&sched->base);
+
+	/* Force complete all unfinished jobs. */
+	spin_lock_irqsave(&sched->lock, flags);
+	list_for_each_entry_safe(job, next, &sched->job_list, link)
+		list_move_tail(&job->link, &list);
+	spin_unlock_irqrestore(&sched->lock, flags);
+
+	list_for_each_entry(job, &list, link)
+		hrtimer_cancel(&job->timer);
+
+	spin_lock_irqsave(&sched->lock, flags);
+	list_for_each_entry_safe(job, next, &list, link)
+		drm_mock_sched_job_complete(job);
+	spin_unlock_irqrestore(&sched->lock, flags);
+
+	/*
+	 * Free completed jobs and jobs not yet processed by the DRM scheduler
+	 * free worker.
+	 */
+	spin_lock_irqsave(&sched->lock, flags);
+	list_for_each_entry_safe(job, next, &sched->done_list, link)
+		list_move_tail(&job->link, &list);
+	spin_unlock_irqrestore(&sched->lock, flags);
+
+	list_for_each_entry_safe(job, next, &list, link)
+		mock_sched_free_job(&job->base);
+
+	drm_sched_fini(&sched->base);
+}
+
+/**
+ * drm_mock_sched_advance - Advances the mock scheduler timeline
+ *
+ * @sched: Scheduler timeline to advance
+ * @num: By how many jobs to advance
+ *
+ * Advancing the scheduler timeline by a number of seqnos will trigger
+ * signalling of the hardware fences and unlinking the jobs from the internal
+ * scheduler tracking.
+ *
+ * This can be used from test cases which want complete control of the simulated
+ * job execution timing. For example submitting one job with no set duration
+ * would never complete it before test cases advances the timeline by one.
+ */
+unsigned int drm_mock_sched_advance(struct drm_mock_scheduler *sched,
+				    unsigned int num)
+{
+	struct drm_mock_sched_job *job, *next;
+	unsigned int found = 0;
+	unsigned long flags;
+	LIST_HEAD(signal);
+
+	spin_lock_irqsave(&sched->lock, flags);
+	if (WARN_ON_ONCE(sched->hw_timeline.cur_seqno + num <
+			 sched->hw_timeline.cur_seqno))
+		goto unlock;
+	sched->hw_timeline.cur_seqno += num;
+	list_for_each_entry_safe(job, next, &sched->job_list, link) {
+		if (sched->hw_timeline.cur_seqno < job->hw_fence.seqno)
+			break;
+
+		drm_mock_sched_job_complete(job);
+		found++;
+	}
+unlock:
+	spin_unlock_irqrestore(&sched->lock, flags);
+
+	return found;
+}
+
+MODULE_DESCRIPTION("DRM mock scheduler and tests");
+MODULE_LICENSE("GPL");