[Intel-gfx] [PATCH 04/22] drm/i915: Remove request retirement before each batch

[Chris Wilson]

This reimplements the denial-of-service protection against igt from
commit 227f782e4667 ("drm/i915: Retire requests before creating a new
one") and transfers the stall from before each batch into get_pages().
The issue is that the stall is increasing latency between batches which
is detrimental in some cases (especially coupled with execlists) to
keeping the GPU well fed. Also we have made the observation that retiring
requests can of itself free objects (and requests) and therefore makes
a good first step when shrinking.

v2: Recycle objects prior to i915_gem_object_get_pages()
v3: Remove the reference to the ring from i915_gem_requests_ring() as it
operates on an intel_engine_cs.

Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
---
 drivers/gpu/drm/i915/i915_drv.h            | 1 -
 drivers/gpu/drm/i915/i915_gem.c            | 7 +++++--
 drivers/gpu/drm/i915/i915_gem_execbuffer.c | 2 --
 drivers/gpu/drm/i915/i915_gem_request.c    | 4 ++--
 4 files changed, 7 insertions(+), 7 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
index fbda38f25c6b..2de3d16f7b80 100644
--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/drivers/gpu/drm/i915/i915_drv.h
@@ -3169,7 +3169,6 @@ struct drm_i915_gem_request *
 i915_gem_find_active_request(struct intel_engine_cs *engine);
 
 void i915_gem_retire_requests(struct drm_i915_private *dev_priv);
-void i915_gem_retire_requests_ring(struct intel_engine_cs *engine);
 
 static inline u32 i915_reset_counter(struct i915_gpu_error *error)
 {
diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
index bf652dc88024..68dbe4f7940c 100644
--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -2244,7 +2244,6 @@ int
 i915_gem_object_get_pages(struct drm_i915_gem_object *obj)
 {
 	struct drm_i915_private *dev_priv = to_i915(obj->base.dev);
-	const struct drm_i915_gem_object_ops *ops = obj->ops;
 	int ret;
 
 	if (obj->pages)
@@ -2257,7 +2256,10 @@ i915_gem_object_get_pages(struct drm_i915_gem_object *obj)
 
 	BUG_ON(obj->pages_pin_count);
 
-	ret = ops->get_pages(obj);
+	/* Recycle as many active objects as possible first */
+	i915_gem_retire_requests(dev_priv);
+
+	ret = obj->ops->get_pages(obj);
 	if (ret)
 		return ret;
 
@@ -4437,6 +4439,7 @@ i915_gem_cleanup_engines(struct drm_device *dev)
 static void
 init_engine_lists(struct intel_engine_cs *engine)
 {
+	/* Early initialisation so that core GEM works during engine setup */
 	INIT_LIST_HEAD(&engine->request_list);
 }
 
diff --git a/drivers/gpu/drm/i915/i915_gem_execbuffer.c b/drivers/gpu/drm/i915/i915_gem_execbuffer.c
index 5e3b5054f72d..0593ea3ba211 100644
--- a/drivers/gpu/drm/i915/i915_gem_execbuffer.c
+++ b/drivers/gpu/drm/i915/i915_gem_execbuffer.c
@@ -781,8 +781,6 @@ i915_gem_execbuffer_reserve(struct intel_engine_cs *engine,
 	bool has_fenced_gpu_access = INTEL_GEN(engine->i915) < 4;
 	int retry;
 
-	i915_gem_retire_requests_ring(engine);
-
 	vm = list_first_entry(vmas, struct i915_vma, exec_list)->vm;
 
 	INIT_LIST_HEAD(&ordered_vmas);
diff --git a/drivers/gpu/drm/i915/i915_gem_request.c b/drivers/gpu/drm/i915/i915_gem_request.c
index 07f08e546915..3395c955a532 100644
--- a/drivers/gpu/drm/i915/i915_gem_request.c
+++ b/drivers/gpu/drm/i915/i915_gem_request.c
@@ -717,7 +717,7 @@ complete:
 	return ret;
 }
 
-void i915_gem_retire_requests_ring(struct intel_engine_cs *engine)
+static void engine_retire_requests(struct intel_engine_cs *engine)
 {
 	struct drm_i915_gem_request *request, *next;
 
@@ -741,7 +741,7 @@ void i915_gem_retire_requests(struct drm_i915_private *dev_priv)
 	GEM_BUG_ON(!dev_priv->gt.awake);
 
 	for_each_engine(engine, dev_priv) {
-		i915_gem_retire_requests_ring(engine);
+		engine_retire_requests(engine);
 		if (list_empty(&engine->request_list))
 			dev_priv->gt.active_engines &= ~intel_engine_flag(engine);
 	}
-- 
2.8.1