drm/i915: Store the reset counter when constructing a request

As the request is only valid during the same global reset epoch, we can
record the current reset_counter when constructing the request and reuse
it when waiting upon that request in future. This removes a very hairy
atomic check serialised by the struct_mutex at the time of waiting and
allows us to transfer those waits to a central dispatcher for all
waiters and all requests.

PS: With per-engine resets, we obviously cannot assume a global reset
epoch for the requests - a per-engine epoch makes the most sense. The
challenge then is how to handle checking in the waiter for when to break
the wait, as the fine-grained reset may also want to requeue the
request (i.e. the assumption that just because the epoch changes the
request is completed may be broken - or we just avoid breaking that
assumption with the fine-grained resets).

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/1460565315-7748-7-git-send-email-chris@chris-wilson.co.uk

1 files changed, 1 insertions, 4 deletions

diff --git a/drivers/gpu/drm/i915/i915_gem_userptr.c b/drivers/gpu/drm/i915/i915_gem_userptr.c
index bebaf75d5348..e6b5938ce6e2 100644
--- a/drivers/gpu/drm/i915/i915_gem_userptr.c
+++ b/drivers/gpu/drm/i915/i915_gem_userptr.c
@@ -65,7 +65,6 @@ static void wait_rendering(struct drm_i915_gem_object *obj)
 {
 	struct drm_device *dev = obj->base.dev;
 	struct drm_i915_gem_request *requests[I915_NUM_ENGINES];
-	unsigned reset_counter;
 	int i, n;
 
 	if (!obj->active)
@@ -82,12 +81,10 @@ static void wait_rendering(struct drm_i915_gem_object *obj)
 		requests[n++] = i915_gem_request_reference(req);
 	}
 
-	reset_counter = atomic_read(&to_i915(dev)->gpu_error.reset_counter);
 	mutex_unlock(&dev->struct_mutex);
 
 	for (i = 0; i < n; i++)
-		__i915_wait_request(requests[i], reset_counter, false,
-				    NULL, NULL);
+		__i915_wait_request(requests[i], false, NULL, NULL);
 
 	mutex_lock(&dev->struct_mutex);