drm/i915: Retire requests along rings

In the next patch, rings are the central timeline as requests may jump
between engines. Therefore in the future as we retire in order along the
engine timeline, we may retire out-of-order within a ring (as the ring now
occurs along multiple engines), leading to much hilarity in miscomputing
the position of ring->head.

As an added bonus, retiring along the ring reduces the penalty of having
one execlists client do cleanup for another (old legacy submission
shares a ring between all clients). The downside is that slow and
irregular (off the critical path) process of cleaning up stale requests
after userspace becomes a modicum less efficient.

In the long run, it will become apparent that the ordered
ring->request_list matches the ring->timeline, a fun challenge for the
future will be unifying the two lists to avoid duplication!

v2: We need both engine-order and ring-order processing to maintain our
knowledge of where individual rings have completed upto as well as
knowing what was last executing on any engine. And finally by decoupling
retiring the contexts on the engine and the timelines along the rings,
we do have to keep a reference to the context on each request
(previously it was guaranteed by the context being pinned).

v3: Not just a reference to the context, but we need to keep it pinned
as we manipulate the rings; i.e. we need a pin for both the manipulation
of the engine state during its retirements, and a separate pin for the
manipulation of the ring state.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180430131503.5375-3-chris@chris-wilson.co.uk

1 files changed, 20 insertions, 7 deletions

diff --git a/drivers/gpu/drm/i915/selftests/mock_engine.c b/drivers/gpu/drm/i915/selftests/mock_engine.c
index b82420c6b810..d95fc481e5c1 100644
--- a/drivers/gpu/drm/i915/selftests/mock_engine.c
+++ b/drivers/gpu/drm/i915/selftests/mock_engine.c
@@ -147,9 +147,18 @@ static struct intel_ring *mock_ring(struct intel_engine_cs *engine)
 	INIT_LIST_HEAD(&ring->request_list);
 	intel_ring_update_space(ring);
 
+	list_add(&ring->link, &engine->i915->gt.rings);
+
 	return ring;
 }
 
+static void mock_ring_free(struct intel_ring *ring)
+{
+	list_del(&ring->link);
+
+	kfree(ring);
+}
+
 struct intel_engine_cs *mock_engine(struct drm_i915_private *i915,
 				    const char *name,
 				    int id)
@@ -162,12 +171,6 @@ struct intel_engine_cs *mock_engine(struct drm_i915_private *i915,
 	if (!engine)
 		return NULL;
 
-	engine->base.buffer = mock_ring(&engine->base);
-	if (!engine->base.buffer) {
-		kfree(engine);
-		return NULL;
-	}
-
 	/* minimal engine setup for requests */
 	engine->base.i915 = i915;
 	snprintf(engine->base.name, sizeof(engine->base.name), "%s", name);
@@ -192,7 +195,16 @@ struct intel_engine_cs *mock_engine(struct drm_i915_private *i915,
 	timer_setup(&engine->hw_delay, hw_delay_complete, 0);
 	INIT_LIST_HEAD(&engine->hw_queue);
 
+	engine->base.buffer = mock_ring(&engine->base);
+	if (!engine->base.buffer)
+		goto err_breadcrumbs;
+
 	return &engine->base;
+
+err_breadcrumbs:
+	intel_engine_fini_breadcrumbs(&engine->base);
+	kfree(engine);
+	return NULL;
 }
 
 void mock_engine_flush(struct intel_engine_cs *engine)
@@ -226,8 +238,9 @@ void mock_engine_free(struct intel_engine_cs *engine)
 	if (engine->last_retired_context)
 		intel_context_unpin(engine->last_retired_context, engine);
 
+	mock_ring_free(engine->buffer);
+
 	intel_engine_fini_breadcrumbs(engine);
 
-	kfree(engine->buffer);
 	kfree(engine);
 }