[Intel-gfx] [PATCH v4 33/38] drm/i915: GPU priority bumping to prevent starvation

[John.C.Harrison at Intel.com]

From: John Harrison <John.C.Harrison at Intel.com>

If a high priority task was to continuously submit batch buffers to
the driver, it could starve out any lower priority task from getting
any GPU time at all. To prevent this, the priority of a queued batch
buffer is bumped each time it does not get submitted to the hardware.

v2: Updated for signed priority values.

For: VIZ-1587
Signed-off-by: John Harrison <John.C.Harrison at Intel.com>
---
 drivers/gpu/drm/i915/i915_debugfs.c   | 28 ++++++++++++++++++++++++++++
 drivers/gpu/drm/i915/i915_scheduler.c | 14 ++++++++++++++
 drivers/gpu/drm/i915/i915_scheduler.h |  1 +
 3 files changed, 43 insertions(+)

diff --git a/drivers/gpu/drm/i915/i915_debugfs.c b/drivers/gpu/drm/i915/i915_debugfs.c
index 73d0f97..1c4c6fe 100644
--- a/drivers/gpu/drm/i915/i915_debugfs.c
+++ b/drivers/gpu/drm/i915/i915_debugfs.c
@@ -1178,6 +1178,33 @@ DEFINE_SIMPLE_ATTRIBUTE(i915_scheduler_priority_max_fops,
 			"%lld\n");
 
 static int
+i915_scheduler_priority_bump_get(void *data, u64 *val)
+{
+	struct drm_device       *dev       = data;
+	struct drm_i915_private *dev_priv  = dev->dev_private;
+	struct i915_scheduler   *scheduler = dev_priv->scheduler;
+
+	*val = (u64) scheduler->priority_level_bump;
+	return 0;
+}
+
+static int
+i915_scheduler_priority_bump_set(void *data, u64 val)
+{
+	struct drm_device       *dev       = data;
+	struct drm_i915_private *dev_priv  = dev->dev_private;
+	struct i915_scheduler   *scheduler = dev_priv->scheduler;
+
+	scheduler->priority_level_bump = (u32) val;
+	return 0;
+}
+
+DEFINE_SIMPLE_ATTRIBUTE(i915_scheduler_priority_bump_fops,
+			i915_scheduler_priority_bump_get,
+			i915_scheduler_priority_bump_set,
+			"%lld\n");
+
+static int
 i915_scheduler_priority_preempt_get(void *data, u64 *val)
 {
 	struct drm_device       *dev       = data;
@@ -5667,6 +5694,7 @@ static const struct i915_debugfs_files {
 	{"i915_next_seqno", &i915_next_seqno_fops},
 	{"i915_scheduler_priority_min", &i915_scheduler_priority_min_fops},
 	{"i915_scheduler_priority_max", &i915_scheduler_priority_max_fops},
+	{"i915_scheduler_priority_bump", &i915_scheduler_priority_bump_fops},
 	{"i915_scheduler_priority_preempt", &i915_scheduler_priority_preempt_fops},
 	{"i915_scheduler_min_flying", &i915_scheduler_min_flying_fops},
 	{"i915_scheduler_file_queue_max", &i915_scheduler_file_queue_max_fops},
diff --git a/drivers/gpu/drm/i915/i915_scheduler.c b/drivers/gpu/drm/i915/i915_scheduler.c
index d19590c..3edf856 100644
--- a/drivers/gpu/drm/i915/i915_scheduler.c
+++ b/drivers/gpu/drm/i915/i915_scheduler.c
@@ -191,6 +191,7 @@ int i915_scheduler_init(struct drm_device *dev)
 	/* Default tuning values: */
 	scheduler->priority_level_min     = -1023;
 	scheduler->priority_level_max     = 1023;
+	scheduler->priority_level_bump    = 50;
 	scheduler->priority_level_preempt = 900;
 	scheduler->min_flying             = 2;
 	scheduler->file_queue_max         = 64;
@@ -1352,6 +1353,19 @@ static int i915_scheduler_submit(struct intel_engine_cs *ring, bool was_locked)
 		ret = i915_scheduler_pop_from_queue_locked(ring, &node, &flags);
 	} while (ret == 0);
 
+	/*
+	 * Bump the priority of everything that was not submitted to prevent
+	 * starvation of low priority tasks by a spamming high priority task.
+	 */
+	i915_scheduler_priority_bump_clear(scheduler);
+	list_for_each_entry(node, &scheduler->node_queue[ring->id], link) {
+		if (!I915_SQS_IS_QUEUED(node))
+			continue;
+
+		i915_scheduler_priority_bump(scheduler, node,
+					     scheduler->priority_level_bump);
+	}
+
 	spin_unlock_irqrestore(&scheduler->lock, flags);
 
 	if (!was_locked)
diff --git a/drivers/gpu/drm/i915/i915_scheduler.h b/drivers/gpu/drm/i915/i915_scheduler.h
index 73bf321..d7aa542 100644
--- a/drivers/gpu/drm/i915/i915_scheduler.h
+++ b/drivers/gpu/drm/i915/i915_scheduler.h
@@ -104,6 +104,7 @@ struct i915_scheduler {
 	/* Tuning parameters: */
 	int32_t             priority_level_min;
 	int32_t             priority_level_max;
+	int32_t             priority_level_bump;
 	int32_t             priority_level_preempt;
 	uint32_t            min_flying;
 	uint32_t            file_queue_max;
-- 
1.9.1