[Intel-gfx] [RFC 37/39] 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.

Change-Id: I0319c7d2f306c61a283f03edda9b5d09a6d3b621
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 3c5c750..509668f 100644
--- a/drivers/gpu/drm/i915/i915_debugfs.c
+++ b/drivers/gpu/drm/i915/i915_debugfs.c
@@ -1152,6 +1152,33 @@ DEFINE_SIMPLE_ATTRIBUTE(i915_scheduler_priority_max_fops,
 			"0x%llx\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,
+			"0x%llx\n");
+
+static int
 i915_scheduler_priority_preempt_get(void *data, u64 *val)
 {
 	struct drm_device       *dev       = data;
@@ -5349,6 +5376,7 @@ static const struct i915_debugfs_files {
 	{"i915_error_state", &i915_error_state_fops},
 	{"i915_next_seqno", &i915_next_seqno_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 631f4e6..8de3f0b 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_max     = ~0U;
+	scheduler->priority_level_bump    =  50;
 	scheduler->priority_level_preempt = 900;
 	scheduler->min_flying             = 2;
 	scheduler->file_queue_max         = 64;
@@ -1568,6 +1569,19 @@ 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 2113e7d..8f3e42f 100644
--- a/drivers/gpu/drm/i915/i915_scheduler.h
+++ b/drivers/gpu/drm/i915/i915_scheduler.h
@@ -119,6 +119,7 @@ struct i915_scheduler {
 
 	/* Tuning parameters: */
 	uint32_t            priority_level_max;
+	uint32_t            priority_level_bump;
 	uint32_t            priority_level_preempt;
 	uint32_t            min_flying;
 	uint32_t            file_queue_max;
-- 
1.9.1