[Intel-gfx] [RFC PATCH 1/2] drm/doc/rfc: i915 GuC submission / DRM scheduler

[Tvrtko Ursulin]

On 27/05/2021 00:33, Matthew Brost wrote:
> Add entry for i915 GuC submission / DRM scheduler integration plan.
> Follow up patch with details of new parallel submission uAPI to come.
> 
> v2:
>   (Daniel Vetter)
>    - Expand explaination of why bonding isn't supported for GuC
>      submission
>    - CC some of the DRM scheduler maintainers
>    - Add priority inheritance / boosting use case
>    - Add reasoning for removing in order assumptions
>   (Daniel Stone)
>    - Add links to priority spec

Where will the outstanding items like, from the top of my head only, 
error capture and open source logging tool be tracked? I thought here 
but maybe not.

Regards,

Tvrtko

> Cc: Christian König <christian.koenig at amd.com>
> Cc: Luben Tuikov <luben.tuikov at amd.com>
> Cc: Alex Deucher <alexander.deucher at amd.com>
> Cc: Steven Price <steven.price at arm.com>
> Cc: Jon Bloomfield <jon.bloomfield at intel.com>
> Cc: Jason Ekstrand <jason at jlekstrand.net>
> Cc: Dave Airlie <airlied at gmail.com>
> Cc: Daniel Vetter <daniel.vetter at intel.com>
> Cc: Jason Ekstrand <jason at jlekstrand.net>
> Cc: dri-devel at lists.freedesktop.org
> Signed-off-by: Matthew Brost <matthew.brost at intel.com>
> ---
>   Documentation/gpu/rfc/i915_scheduler.rst | 85 ++++++++++++++++++++++++
>   Documentation/gpu/rfc/index.rst          |  4 ++
>   2 files changed, 89 insertions(+)
>   create mode 100644 Documentation/gpu/rfc/i915_scheduler.rst
> 
> diff --git a/Documentation/gpu/rfc/i915_scheduler.rst b/Documentation/gpu/rfc/i915_scheduler.rst
> new file mode 100644
> index 000000000000..7faa46cde088
> --- /dev/null
> +++ b/Documentation/gpu/rfc/i915_scheduler.rst
> @@ -0,0 +1,85 @@
> +=========================================
> +I915 GuC Submission/DRM Scheduler Section
> +=========================================
> +
> +Upstream plan
> +=============
> +For upstream the overall plan for landing GuC submission and integrating the
> +i915 with the DRM scheduler is:
> +
> +* Merge basic GuC submission
> +	* Basic submission support for all gen11+ platforms
> +	* Not enabled by default on any current platforms but can be enabled via
> +	  modparam enable_guc
> +	* Lots of rework will need to be done to integrate with DRM scheduler so
> +	  no need to nit pick everything in the code, it just should be
> +	  functional, no major coding style / layering errors, and not regress
> +	  execlists
> +	* Update IGTs / selftests as needed to work with GuC submission
> +	* Enable CI on supported platforms for a baseline
> +	* Rework / get CI heathly for GuC submission in place as needed
> +* Merge new parallel submission uAPI
> +	* Bonding uAPI completely incompatible with GuC submission, plus it has
> +	  severe design issues in general, which is why we want to retire it no
> +	  matter what
> +	* New uAPI adds I915_CONTEXT_ENGINES_EXT_PARALLEL context setup step
> +	  which configures a slot with N contexts
> +	* After I915_CONTEXT_ENGINES_EXT_PARALLEL a user can submit N batches to
> +	  a slot in a single execbuf IOCTL and the batches run on the GPU in
> +	  paralllel
> +	* Initially only for GuC submission but execlists can be supported if
> +	  needed
> +* Convert the i915 to use the DRM scheduler
> +	* GuC submission backend fully integrated with DRM scheduler
> +		* All request queues removed from backend (e.g. all backpressure
> +		  handled in DRM scheduler)
> +		* Resets / cancels hook in DRM scheduler
> +		* Watchdog hooks into DRM scheduler
> +		* Lots of complexity of the GuC backend can be pulled out once
> +		  integrated with DRM scheduler (e.g. state machine gets
> +		  simplier, locking gets simplier, etc...)
> +	* Execlist backend will do the minimum required to hook in the DRM
> +	  scheduler so it can live next to the fully integrated GuC backend
> +		* Legacy interface
> +		* Features like timeslicing / preemption / virtual engines would
> +		  be difficult to integrate with the DRM scheduler and these
> +		  features are not required for GuC submission as the GuC does
> +		  these things for us
> +		* ROI low on fully integrating into DRM scheduler
> +		* Fully integrating would add lots of complexity to DRM
> +		  scheduler
> +	* Port i915 priority inheritance / boosting feature in DRM scheduler
> +		* Used for i915 page flip, may be useful to other DRM drivers as
> +		  well
> +		* Will be an optional feature in the DRM scheduler
> +	* Remove in-order completion assumptions from DRM scheduler
> +		* Even when using the DRM scheduler the backends will handle
> +		  preemption, timeslicing, etc... so it is possible for jobs to
> +		  finish out of order
> +	* Pull out i915 priority levels and use DRM priority levels
> +	* Optimize DRM scheduler as needed
> +
> +New uAPI for basic GuC submission
> +=================================
> +No major changes are required to the uAPI for basic GuC submission. The only
> +change is a new scheduler attribute: I915_SCHEDULER_CAP_STATIC_PRIORITY_MAP.
> +This attribute indicates the 2k i915 user priority levels are statically mapped
> +into 3 levels as follows:
> +
> +* -1k to -1 Low priority
> +* 0 Medium priority
> +* 1 to 1k High priority
> +
> +This is needed because the GuC only has 4 priority bands. The highest priority
> +band is reserved with the kernel. This aligns with the DRM scheduler priority
> +levels too.
> +
> +Spec references:
> +----------------
> +https://www.khronos.org/registry/EGL/extensions/IMG/EGL_IMG_context_priority.txt
> +https://www.khronos.org/registry/vulkan/specs/1.2-extensions/html/chap5.html#devsandqueues-priority
> +https://spec.oneapi.com/level-zero/latest/core/api.html#ze-command-queue-priority-t
> +
> +New parallel submission uAPI
> +============================
> +Details to come in a following patch.
> diff --git a/Documentation/gpu/rfc/index.rst b/Documentation/gpu/rfc/index.rst
> index 05670442ca1b..91e93a705230 100644
> --- a/Documentation/gpu/rfc/index.rst
> +++ b/Documentation/gpu/rfc/index.rst
> @@ -19,3 +19,7 @@ host such documentation:
>   .. toctree::
>   
>       i915_gem_lmem.rst
> +
> +.. toctree::
> +
> +    i915_scheduler.rst
>