drm/i915/scheduler: Signal the arrival of a new request

The start of the scheduler, add a hook into request submission for the
scheduler to see the arrival of new requests and prepare its runqueues.
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20161114204105.29171-6-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/i915_drv.c

@@ -323,6 +323,10 @@ static int i915_getparam(struct drm_device *dev, void *data,
 		 */
 		value = i915_gem_mmap_gtt_version();
 		break;
+	case I915_PARAM_HAS_SCHEDULER:
+		value = dev_priv->engine[RCS] &&
+			dev_priv->engine[RCS]->schedule;
+		break;
 	case I915_PARAM_MMAP_VERSION:
 		/* Remember to bump this if the version changes! */
 	case I915_PARAM_HAS_GEM:

drivers/gpu/drm/i915/i915_gem_request.c

@@ -762,6 +762,19 @@ void __i915_add_request(struct drm_i915_gem_request *request, bool flush_caches)
 
 	i915_gem_mark_busy(engine);
 
+	/* Let the backend know a new request has arrived that may need
+	 * to adjust the existing execution schedule due to a high priority
+	 * request - i.e. we may want to preempt the current request in order
+	 * to run a high priority dependency chain *before* we can execute this
+	 * request.
+	 *
+	 * This is called before the request is ready to run so that we can
+	 * decide whether to preempt the entire chain so that it is ready to
+	 * run at the earliest possible convenience.
+	 */
+	if (engine->schedule)
+		engine->schedule(request, 0);
+
 	local_bh_disable();
 	i915_sw_fence_commit(&request->submit);
 	local_bh_enable(); /* Kick the execlists tasklet if just scheduled */

drivers/gpu/drm/i915/intel_engine_cs.c

@@ -102,6 +102,9 @@ intel_engine_setup(struct drm_i915_private *dev_priv,
 	engine->mmio_base = info->mmio_base;
 	engine->irq_shift = info->irq_shift;
 
+	/* Nothing to do here, execute in order of dependencies */
+	engine->schedule = NULL;
+
 	dev_priv->engine[id] = engine;
 	return 0;
 }

drivers/gpu/drm/i915/intel_ringbuffer.h

@@ -267,6 +267,15 @@ struct intel_engine_cs {
 	 */
 	void		(*submit_request)(struct drm_i915_gem_request *req);
 
+	/* Call when the priority on a request has changed and it and its
+	 * dependencies may need rescheduling. Note the request itself may
+	 * not be ready to run!
+	 *
+	 * Called under the struct_mutex.
+	 */
+	void		(*schedule)(struct drm_i915_gem_request *request,
+				    int priority);
+
 	/* Some chipsets are not quite as coherent as advertised and need
 	 * an expensive kick to force a true read of the up-to-date seqno.
 	 * However, the up-to-date seqno is not always required and the last

include/uapi/drm/i915_drm.h

@@ -389,6 +389,11 @@ typedef struct drm_i915_irq_wait {
 #define I915_PARAM_MIN_EU_IN_POOL	 39
 #define I915_PARAM_MMAP_GTT_VERSION	 40
 
+/* Query whether DRM_I915_GEM_EXECBUFFER2 supports user defined execution
+ * priorities and the driver will attempt to execute batches in priority order.
+ */
+#define I915_PARAM_HAS_SCHEDULER	 41
+
 typedef struct drm_i915_getparam {
 	__s32 param;
 	/*