Add entry for i915 new parallel submission uAPI plan.
v2:
(Daniel Vetter):
- Expand logical order explaination
- Add dummy header
- Only allow N BBs in execbuf IOCTL
- Configure parallel submission per slot not per gem context
v3:
(Marcin Ślusarz):
- Lot's of typos / bad english fixed
(Tvrtko Ursulin):
- Consistent pseudo code, clean up wording in descriptions
v4:
(Daniel Vetter)
- Drop flags
- Add kernel doc
- Reword a few things / fix typos
(Tvrtko)
- Reword a few things / fix typos
v5:
(Checkpatch)
- Fix typos
(Docs)
- Fix warning
Cc: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxx>
Cc: Tony Ye <tony.ye@xxxxxxxxx>
CC: Carl Zhang <carl.zhang@xxxxxxxxx>
Cc: Daniel Vetter <daniel.vetter@xxxxxxxxx>
Cc: Jason Ekstrand <jason@xxxxxxxxxxxxxx>
Signed-off-by: Matthew Brost <matthew.brost@xxxxxxxxx>
Acked-by: Daniel Vetter <daniel.vetter@xxxxxxxx>
Acked-by: Tony Ye <tony.ye@xxxxxxxxx>
---
Documentation/gpu/rfc/i915_parallel_execbuf.h | 122 ++++++++++++++++++
Documentation/gpu/rfc/i915_scheduler.rst | 59 ++++++++-
2 files changed, 180 insertions(+), 1 deletion(-)
create mode 100644 Documentation/gpu/rfc/i915_parallel_execbuf.h
diff --git a/Documentation/gpu/rfc/i915_parallel_execbuf.h b/Documentation/gpu/rfc/i915_parallel_execbuf.h
new file mode 100644
index 000000000000..8cbe2c4e0172
--- /dev/null
+++ b/Documentation/gpu/rfc/i915_parallel_execbuf.h
@@ -0,0 +1,122 @@
+/* SPDX-License-Identifier: MIT */
+/*
+ * Copyright © 2021 Intel Corporation
+ */
+
+#define I915_CONTEXT_ENGINES_EXT_PARALLEL_SUBMIT 2 /* see i915_context_engines_parallel_submit */
+
+/**
+ * struct drm_i915_context_engines_parallel_submit - Configure engine for
+ * parallel submission.
+ *
+ * Setup a slot in the context engine map to allow multiple BBs to be submitted
+ * in a single execbuf IOCTL. Those BBs will then be scheduled to run on the GPU
+ * in parallel. Multiple hardware contexts are created internally in the i915
+ * run these BBs. Once a slot is configured for N BBs only N BBs can be
+ * submitted in each execbuf IOCTL and this is implicit behavior e.g. The user
+ * doesn't tell the execbuf IOCTL there are N BBs, the execbuf IOCTL knows how
+ * many BBs there are based on the slot's configuration. The N BBs are the last
+ * N buffer objects or first N if I915_EXEC_BATCH_FIRST is set.
+ *
+ * The default placement behavior is to create implicit bonds between each
+ * context if each context maps to more than 1 physical engine (e.g. context is
+ * a virtual engine). Also we only allow contexts of same engine class and these
+ * contexts must be in logically contiguous order. Examples of the placement
+ * behavior described below. Lastly, the default is to not allow BBs to
+ * preempted mid BB rather insert coordinated preemption on all hardware
+ * contexts between each set of BBs. Flags may be added in the future to change
+ * both of these default behaviors.
+ *
+ * Returns -EINVAL if hardware context placement configuration is invalid or if
+ * the placement configuration isn't supported on the platform / submission
+ * interface.
+ * Returns -ENODEV if extension isn't supported on the platform / submission
+ * interface.
+ *
+ * .. code-block:: none
+ *
+ * Example 1 pseudo code:
+ * CS[X] = generic engine of same class, logical instance X
+ * INVALID = I915_ENGINE_CLASS_INVALID, I915_ENGINE_CLASS_INVALID_NONE
+ * set_engines(INVALID)
+ * set_parallel(engine_index=0, width=2, num_siblings=1,
+ * engines=CS[0],CS[1])
+ *
+ * Results in the following valid placement:
+ * CS[0], CS[1]
+ *
+ * Example 2 pseudo code:
+ * CS[X] = generic engine of same class, logical instance X
+ * INVALID = I915_ENGINE_CLASS_INVALID, I915_ENGINE_CLASS_INVALID_NONE
+ * set_engines(INVALID)
+ * set_parallel(engine_index=0, width=2, num_siblings=2,
+ * engines=CS[0],CS[2],CS[1],CS[3])
+ *
+ * Results in the following valid placements:
+ * CS[0], CS[1]
+ * CS[2], CS[3]
+ *
+ * This can also be thought of as 2 virtual engines described by 2-D array
+ * in the engines the field with bonds placed between each index of the
+ * virtual engines. e.g. CS[0] is bonded to CS[1], CS[2] is bonded to
+ * CS[3].
+ * VE[0] = CS[0], CS[2]
+ * VE[1] = CS[1], CS[3]
+ *
+ * Example 3 pseudo code:
+ * CS[X] = generic engine of same class, logical instance X
+ * INVALID = I915_ENGINE_CLASS_INVALID, I915_ENGINE_CLASS_INVALID_NONE
+ * set_engines(INVALID)
+ * set_parallel(engine_index=0, width=2, num_siblings=2,
+ * engines=CS[0],CS[1],CS[1],CS[3])
+ *
+ * Results in the following valid and invalid placements:
+ * CS[0], CS[1]
+ * CS[1], CS[3] - Not logical contiguous, return -EINVAL
+ */
+struct drm_i915_context_engines_parallel_submit {
+ /**
+ * @base: base user extension.
+ */
+ struct i915_user_extension base;
+
+ /**
+ * @engine_index: slot for parallel engine
+ */
+ __u16 engine_index;
+
+ /**
+ * @width: number of contexts per parallel engine
+ */
+ __u16 width;
+
+ /**
+ * @num_siblings: number of siblings per context
+ */
+ __u16 num_siblings;
+
+ /**
+ * @mbz16: reserved for future use; must be zero
+ */
+ __u16 mbz16;
+
+ /**
+ * @flags: all undefined flags must be zero, currently not defined flags
+ */
+ __u64 flags;
+
+ /**
+ * @mbz64: reserved for future use; must be zero
+ */
+ __u64 mbz64[3];
+
+ /**
+ * @engines: 2-d array of engine instances to configure parallel engine
+ *
+ * length = width (i) * num_siblings (j)
+ * index = j + i * num_siblings
+ */
+ struct i915_engine_class_instance engines[0];
+
+} __packed;
+
diff --git a/Documentation/gpu/rfc/i915_scheduler.rst b/Documentation/gpu/rfc/i915_scheduler.rst
index 7acd386a6b49..cbda75065dad 100644
--- a/Documentation/gpu/rfc/i915_scheduler.rst
+++ b/Documentation/gpu/rfc/i915_scheduler.rst
@@ -88,4 +88,61 @@ Spec references:
New parallel submission uAPI
============================
-Details to come in a following patch.
+The existing bonding uAPI is completely broken with GuC submission because
+whether a submission is a single context submit or parallel submit isn't known
+until execbuf time activated via the I915_SUBMIT_FENCE. To submit multiple
+contexts in parallel with the GuC the context must be explicitly registered with
+N contexts and all N contexts must be submitted in a single command to the GuC.
+The GuC interfaces do not support dynamically changing between N contexts as the
+bonding uAPI does. Hence the need for a new parallel submission interface. Also
+the legacy bonding uAPI is quite confusing and not intuitive at all. Furthermore
+I915_SUBMIT_FENCE is by design a future fence, so not really something we should
+continue to support.
+
+The new parallel submission uAPI consists of 3 parts:
+
+* Export engines logical mapping
+* A 'set_parallel' extension to configure contexts for parallel
+ submission
+* Extend execbuf2 IOCTL to support submitting N BBs in a single IOCTL
+
+Export engines logical mapping
+------------------------------
+Certain use cases require BBs to be placed on engine instances in logical order
+(e.g. split-frame on gen11+). The logical mapping of engine instances can change
+based on fusing. Rather than making UMDs be aware of fusing, simply expose the
+logical mapping with the existing query engine info IOCTL. Also the GuC
+submission interface currently only supports submitting multiple contexts to
+engines in logical order which is a new requirement compared to execlists.
+Lastly, all current platforms have at most 2 engine instances and the logical
+order is the same as uAPI order. This will change on platforms with more than 2
+engine instances.
+
+A single bit will be added to drm_i915_engine_info.flags indicating that the
+logical instance has been returned and a new field,
+drm_i915_engine_info.logical_instance, returns the logical instance.
+
+A 'set_parallel' extension to configure contexts for parallel submission
+------------------------------------------------------------------------
+The 'set_parallel' extension configures a slot for parallel submission of N BBs.
+It is a setup step that must be called before using any of the contexts. See
+I915_CONTEXT_ENGINES_EXT_LOAD_BALANCE or I915_CONTEXT_ENGINES_EXT_BOND for
+similar existing examples. Once a slot is configured for parallel submission the
+execbuf2 IOCTL can be called submitting N BBs in a single IOCTL. Initially only
+supports GuC submission. Execlists supports can be added later if needed.
+
+Add I915_CONTEXT_ENGINES_EXT_PARALLEL_SUBMIT and
+drm_i915_context_engines_parallel_submit to the uAPI to implement this
+extension.
+
+.. kernel-doc:: Documentation/gpu/rfc/i915_parallel_execbuf.h
+ :functions: drm_i915_context_engines_parallel_submit
+
+Extend execbuf2 IOCTL to support submitting N BBs in a single IOCTL
+-------------------------------------------------------------------
+Contexts that have been configured with the 'set_parallel' extension can only
+submit N BBs in a single execbuf2 IOCTL. The BBs are either the last N objects
+in the drm_i915_gem_exec_object2 list or the first N if I915_EXEC_BATCH_FIRST is
+set. The number of BBs is implicit based on the slot submitted and how it has
+been configured by 'set_parallel' or other extensions. No uAPI changes are
+required to the execbuf2 IOCTL.
--
2.28.0
