1=========================================
2I915 GuC Submission/DRM Scheduler Section
3=========================================
4
5Upstream plan
6=============
7For upstream the overall plan for landing GuC submission and integrating the
8i915 with the DRM scheduler is:
9
10* Merge basic GuC submission
11	* Basic submission support for all gen11+ platforms
12	* Not enabled by default on any current platforms but can be enabled via
13	  modparam enable_guc
14	* Lots of rework will need to be done to integrate with DRM scheduler so
15	  no need to nit pick everything in the code, it just should be
16	  functional, no major coding style / layering errors, and not regress
17	  execlists
18	* Update IGTs / selftests as needed to work with GuC submission
19	* Enable CI on supported platforms for a baseline
20	* Rework / get CI heathly for GuC submission in place as needed
21* Merge new parallel submission uAPI
22	* Bonding uAPI completely incompatible with GuC submission, plus it has
23	  severe design issues in general, which is why we want to retire it no
24	  matter what
25	* New uAPI adds I915_CONTEXT_ENGINES_EXT_PARALLEL context setup step
26	  which configures a slot with N contexts
27	* After I915_CONTEXT_ENGINES_EXT_PARALLEL a user can submit N batches to
28	  a slot in a single execbuf IOCTL and the batches run on the GPU in
29	  paralllel
30	* Initially only for GuC submission but execlists can be supported if
31	  needed
32* Convert the i915 to use the DRM scheduler
33	* GuC submission backend fully integrated with DRM scheduler
34		* All request queues removed from backend (e.g. all backpressure
35		  handled in DRM scheduler)
36		* Resets / cancels hook in DRM scheduler
37		* Watchdog hooks into DRM scheduler
38		* Lots of complexity of the GuC backend can be pulled out once
39		  integrated with DRM scheduler (e.g. state machine gets
40		  simplier, locking gets simplier, etc...)
41	* Execlists backend will minimum required to hook in the DRM scheduler
42		* Legacy interface
43		* Features like timeslicing / preemption / virtual engines would
44		  be difficult to integrate with the DRM scheduler and these
45		  features are not required for GuC submission as the GuC does
46		  these things for us
47		* ROI low on fully integrating into DRM scheduler
48		* Fully integrating would add lots of complexity to DRM
49		  scheduler
50	* Port i915 priority inheritance / boosting feature in DRM scheduler
51		* Used for i915 page flip, may be useful to other DRM drivers as
52		  well
53		* Will be an optional feature in the DRM scheduler
54	* Remove in-order completion assumptions from DRM scheduler
55		* Even when using the DRM scheduler the backends will handle
56		  preemption, timeslicing, etc... so it is possible for jobs to
57		  finish out of order
58	* Pull out i915 priority levels and use DRM priority levels
59	* Optimize DRM scheduler as needed
60
61TODOs for GuC submission upstream
62=================================
63
64* Need an update to GuC firmware / i915 to enable error state capture
65* Open source tool to decode GuC logs
66* Public GuC spec
67
68New uAPI for basic GuC submission
69=================================
70No major changes are required to the uAPI for basic GuC submission. The only
71change is a new scheduler attribute: I915_SCHEDULER_CAP_STATIC_PRIORITY_MAP.
72This attribute indicates the 2k i915 user priority levels are statically mapped
73into 3 levels as follows:
74
75* -1k to -1 Low priority
76* 0 Medium priority
77* 1 to 1k High priority
78
79This is needed because the GuC only has 4 priority bands. The highest priority
80band is reserved with the kernel. This aligns with the DRM scheduler priority
81levels too.
82
83Spec references:
84----------------
85* https://www.khronos.org/registry/EGL/extensions/IMG/EGL_IMG_context_priority.txt
86* https://www.khronos.org/registry/vulkan/specs/1.2-extensions/html/chap5.html#devsandqueues-priority
87* https://spec.oneapi.com/level-zero/latest/core/api.html#ze-command-queue-priority-t
88
89New parallel submission uAPI
90============================
91The existing bonding uAPI is completely broken with GuC submission because
92whether a submission is a single context submit or parallel submit isn't known
93until execbuf time activated via the I915_SUBMIT_FENCE. To submit multiple
94contexts in parallel with the GuC the context must be explicitly registered with
95N contexts and all N contexts must be submitted in a single command to the GuC.
96The GuC interfaces do not support dynamically changing between N contexts as the
97bonding uAPI does. Hence the need for a new parallel submission interface. Also
98the legacy bonding uAPI is quite confusing and not intuitive at all. Furthermore
99I915_SUBMIT_FENCE is by design a future fence, so not really something we should
100continue to support.
101
102The new parallel submission uAPI consists of 3 parts:
103
104* Export engines logical mapping
105* A 'set_parallel' extension to configure contexts for parallel
106  submission
107* Extend execbuf2 IOCTL to support submitting N BBs in a single IOCTL
108
109Export engines logical mapping
110------------------------------
111Certain use cases require BBs to be placed on engine instances in logical order
112(e.g. split-frame on gen11+). The logical mapping of engine instances can change
113based on fusing. Rather than making UMDs be aware of fusing, simply expose the
114logical mapping with the existing query engine info IOCTL. Also the GuC
115submission interface currently only supports submitting multiple contexts to
116engines in logical order which is a new requirement compared to execlists.
117Lastly, all current platforms have at most 2 engine instances and the logical
118order is the same as uAPI order. This will change on platforms with more than 2
119engine instances.
120
121A single bit will be added to drm_i915_engine_info.flags indicating that the
122logical instance has been returned and a new field,
123drm_i915_engine_info.logical_instance, returns the logical instance.
124
125A 'set_parallel' extension to configure contexts for parallel submission
126------------------------------------------------------------------------
127The 'set_parallel' extension configures a slot for parallel submission of N BBs.
128It is a setup step that must be called before using any of the contexts. See
129I915_CONTEXT_ENGINES_EXT_LOAD_BALANCE or I915_CONTEXT_ENGINES_EXT_BOND for
130similar existing examples. Once a slot is configured for parallel submission the
131execbuf2 IOCTL can be called submitting N BBs in a single IOCTL. Initially only
132supports GuC submission. Execlists supports can be added later if needed.
133
134Add I915_CONTEXT_ENGINES_EXT_PARALLEL_SUBMIT and
135drm_i915_context_engines_parallel_submit to the uAPI to implement this
136extension.
137
138.. kernel-doc:: Documentation/gpu/rfc/i915_parallel_execbuf.h
139        :functions: drm_i915_context_engines_parallel_submit
140
141Extend execbuf2 IOCTL to support submitting N BBs in a single IOCTL
142-------------------------------------------------------------------
143Contexts that have been configured with the 'set_parallel' extension can only
144submit N BBs in a single execbuf2 IOCTL. The BBs are either the last N objects
145in the drm_i915_gem_exec_object2 list or the first N if I915_EXEC_BATCH_FIRST is
146set. The number of BBs is implicit based on the slot submitted and how it has
147been configured by 'set_parallel' or other extensions. No uAPI changes are
148required to the execbuf2 IOCTL.
149