drm/i915/execlists: Track begin/end of execlists submission sequences

We would like to start doing some bookkeeping at the beginning, between
contexts and at the end of execlists submission. We already mark the
beginning and end using EXECLISTS_ACTIVE_USER, to provide an indication
when the HW is idle. This give us a pair of sequence points we can then
expand on for further bookkeeping.

v2: Refactor guc submission to share the same begin/end.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Cc: Francisco Jerez <currojerez@riseup.net>
Reviewed-by: Francisco Jerez <currojerez@riseup.net>
Reviewed-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180331130626.10712-1-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/intel_guc_submission.c

@@ -728,7 +728,7 @@ done:
 	execlists->first = rb;
 	if (submit) {
 		port_assign(port, last);
-		execlists_set_active(execlists, EXECLISTS_ACTIVE_USER);
+		execlists_user_begin(execlists, execlists->port);
 		guc_submit(engine);
 	}
 
@@ -748,17 +748,20 @@ static void guc_submission_tasklet(unsigned long data)
 	struct execlist_port *port = execlists->port;
 	struct i915_request *rq;
 
-	rq = port_request(&port[0]);
+	rq = port_request(port);
 	while (rq && i915_request_completed(rq)) {
 		trace_i915_request_out(rq);
 		i915_request_put(rq);
 
-		execlists_port_complete(execlists, port);
-
-		rq = port_request(&port[0]);
+		port = execlists_port_complete(execlists, port);
+		if (port_isset(port)) {
+			execlists_user_begin(execlists, port);
+			rq = port_request(port);
+		} else {
+			execlists_user_end(execlists);
+			rq = NULL;
+		}
 	}
-	if (!rq)
-		execlists_clear_active(execlists, EXECLISTS_ACTIVE_USER);
 
 	if (execlists_is_active(execlists, EXECLISTS_ACTIVE_PREEMPT) &&
 	    intel_read_status_page(engine, I915_GEM_HWS_PREEMPT_INDEX) ==

drivers/gpu/drm/i915/intel_lrc.c

@@ -374,6 +374,19 @@ execlists_context_status_change(struct i915_request *rq, unsigned long status)
 				   status, rq);
 }
 
+inline void
+execlists_user_begin(struct intel_engine_execlists *execlists,
+		     const struct execlist_port *port)
+{
+	execlists_set_active_once(execlists, EXECLISTS_ACTIVE_USER);
+}
+
+inline void
+execlists_user_end(struct intel_engine_execlists *execlists)
+{
+	execlists_clear_active(execlists, EXECLISTS_ACTIVE_USER);
+}
+
 static inline void
 execlists_context_schedule_in(struct i915_request *rq)
 {
@@ -711,7 +724,7 @@ unlock:
 	spin_unlock_irq(&engine->timeline->lock);
 
 	if (submit) {
-		execlists_set_active(execlists, EXECLISTS_ACTIVE_USER);
+		execlists_user_begin(execlists, execlists->port);
 		execlists_submit_ports(engine);
 	}
 
@@ -742,7 +755,7 @@ execlists_cancel_port_requests(struct intel_engine_execlists * const execlists)
 		port++;
 	}
 
-	execlists_clear_active(execlists, EXECLISTS_ACTIVE_USER);
+	execlists_user_end(execlists);
 }
 
 static void clear_gtiir(struct intel_engine_cs *engine)
@@ -873,7 +886,7 @@ static void execlists_submission_tasklet(unsigned long data)
 {
 	struct intel_engine_cs * const engine = (struct intel_engine_cs *)data;
 	struct intel_engine_execlists * const execlists = &engine->execlists;
-	struct execlist_port * const port = execlists->port;
+	struct execlist_port *port = execlists->port;
 	struct drm_i915_private *dev_priv = engine->i915;
 	bool fw = false;
 
@@ -1012,10 +1025,28 @@ static void execlists_submission_tasklet(unsigned long data)
 
 			GEM_BUG_ON(count == 0);
 			if (--count == 0) {
+				/*
+				 * On the final event corresponding to the
+				 * submission of this context, we expect either
+				 * an element-switch event or a completion
+				 * event (and on completion, the active-idle
+				 * marker). No more preemptions, lite-restore
+				 * or otherwise.
+				 */
 				GEM_BUG_ON(status & GEN8_CTX_STATUS_PREEMPTED);
 				GEM_BUG_ON(port_isset(&port[1]) &&
 					   !(status & GEN8_CTX_STATUS_ELEMENT_SWITCH));
+				GEM_BUG_ON(!port_isset(&port[1]) &&
+					   !(status & GEN8_CTX_STATUS_ACTIVE_IDLE));
+
+				/*
+				 * We rely on the hardware being strongly
+				 * ordered, that the breadcrumb write is
+				 * coherent (visible from the CPU) before the
+				 * user interrupt and CSB is processed.
+				 */
 				GEM_BUG_ON(!i915_request_completed(rq));
+
 				execlists_context_schedule_out(rq);
 				trace_i915_request_out(rq);
 				i915_request_put(rq);
@@ -1023,17 +1054,14 @@ static void execlists_submission_tasklet(unsigned long data)
 				GEM_TRACE("%s completed ctx=%d\n",
 					  engine->name, port->context_id);
 
-				execlists_port_complete(execlists, port);
+				port = execlists_port_complete(execlists, port);
+				if (port_isset(port))
+					execlists_user_begin(execlists, port);
+				else
+					execlists_user_end(execlists);
 			} else {
 				port_set(port, port_pack(rq, count));
 			}
-
-			/* After the final element, the hw should be idle */
-			GEM_BUG_ON(port_count(port) == 0 &&
-				   !(status & GEN8_CTX_STATUS_ACTIVE_IDLE));
-			if (port_count(port) == 0)
-				execlists_clear_active(execlists,
-						       EXECLISTS_ACTIVE_USER);
 		}
 
 		if (head != execlists->csb_head) {

drivers/gpu/drm/i915/intel_ringbuffer.h

@@ -638,6 +638,13 @@ execlists_set_active(struct intel_engine_execlists *execlists,
 	__set_bit(bit, (unsigned long *)&execlists->active);
 }
 
+static inline bool
+execlists_set_active_once(struct intel_engine_execlists *execlists,
+			  unsigned int bit)
+{
+	return !__test_and_set_bit(bit, (unsigned long *)&execlists->active);
+}
+
 static inline void
 execlists_clear_active(struct intel_engine_execlists *execlists,
 		       unsigned int bit)
@@ -652,6 +659,10 @@ execlists_is_active(const struct intel_engine_execlists *execlists,
 	return test_bit(bit, (unsigned long *)&execlists->active);
 }
 
+void execlists_user_begin(struct intel_engine_execlists *execlists,
+			  const struct execlist_port *port);
+void execlists_user_end(struct intel_engine_execlists *execlists);
+
 void
 execlists_cancel_port_requests(struct intel_engine_execlists * const execlists);
 
@@ -664,7 +675,7 @@ execlists_num_ports(const struct intel_engine_execlists * const execlists)
 	return execlists->port_mask + 1;
 }
 
-static inline void
+static inline struct execlist_port *
 execlists_port_complete(struct intel_engine_execlists * const execlists,
 			struct execlist_port * const port)
 {
@@ -675,6 +686,8 @@ execlists_port_complete(struct intel_engine_execlists * const execlists,
 
 	memmove(port, port + 1, m * sizeof(struct execlist_port));
 	memset(port + m, 0, sizeof(struct execlist_port));
+
+	return port;
 }
 
 static inline unsigned int