[Intel-gfx] [PATCH 05/12] drm/i915/scheduler: Record all dependencies upon request construction

[Chris Wilson]

On Mon, Nov 07, 2016 at 09:12:57AM +0000, Tvrtko Ursulin wrote:
> 
> On 04/11/2016 15:11, Chris Wilson wrote:
> >On Fri, Nov 04, 2016 at 02:44:44PM +0000, Tvrtko Ursulin wrote:
> >>
> >>On 03/11/2016 11:55, Chris Wilson wrote:
> >>>On Thu, Nov 03, 2016 at 11:03:47AM +0000, Tvrtko Ursulin wrote:
> >>>>
> >>>>On 02/11/2016 17:50, Chris Wilson wrote:
> >>>>>+struct i915_dependency {
> >>>>>+	struct i915_priotree *signal;
> >>>>>+	struct list_head pre_link, post_link;
> >>>>>+	unsigned long flags;
> >>>>>+#define I915_DEPENDENCY_ALLOC BIT(0)
> >>>>>+};
> >>>>>+
> >>>>>+struct i915_priotree {
> >>>>>+	struct list_head pre_list; /* who is before us, we depend upon */
> >>>>>+	struct list_head post_list; /* who is after us, they depend upon us */
> >>>>>+};
> >>>>
> >>>>I need a picture to imagine this data structure. :(
> >>>
> >>>The names suck.
> >>
> >>When you wrote this I assumed you would respin shortly with some
> >>better names?
> >
> >Not yet. I kind of like
> >
> >struct i915_dependency {
> >	struct i915_priotree *signaler;
> >	struct list_head signaler_link;
> >	struct list_head listener_link;
> >};
> >
> >struct i915_priotree {
> >	struct list_head signalers_list; /* before us, we depend on them */
> >	struct list_head listeners_list; /* those after, who depend on us */
> >};
> >
> 
> What is the signaler in i915_dependency?

That would be the actual dependency. The fences have a notion of
waiters, but we need to track the signalers in order to perform PI.
Fwiw,

+struct i915_dependency {
+       struct i915_priotree *signaler;
+       struct list_head signal_link;
+       struct list_head wait_link;
+       unsigned long flags;
+#define I915_DEPENDENCY_ALLOC BIT(0)
+};
+
+/* Requests exist in a complex web of interdependencies. Each request
+ * has to wait for some other request to complete before it is ready to be run
+ * (e.g. we have to wait until the pixels have been rendering into a texture
+ * before we can copy from it). We track the readiness of a request in terms
+ * of fences, but we also need to keep the dependency tree for the lifetime
+ * of the request (beyond the life of an individual fence). We use the tree
+ * at various points to reorder the requests whilst keeping the requests
+ * in order with respect to their various dependencies.
+ */
+struct i915_priotree {
+       struct list_head signalers_list; /* those before us, we depend upon */
+       struct list_head waiters_list; /* those after us, they depend upon us */
+};


-- 
Chris Wilson, Intel Open Source Technology Centre