[SYCL][UR][Graph] Require OpenCL simultaneous use

To support the SYCL-Graph extension on an OpenCL backend, we currently
only require the presence of the `cl_khr_command_buffer` extension. This
PR introduces an extra requirement on the
[CL_COMMAND_BUFFER_SIMULTANEOUS_USE_KHR](https://registry.khronos.org/OpenCL/specs/3.0-unified/html/OpenCL_API.html#CL_COMMAND_BUFFER_SIMULTANEOUS_USE_KHR) capability being present.

This is based on the [graph execution
wording](https://github.com/intel/llvm/blob/sycl/sycl/doc/extensions/experimental/sycl_ext_oneapi_graph.asciidoc#765-new-handler-member-functions)
on the definition of `handler::ext_oneapi_graph()` that:

>  Only one instance of graph will execute at any time. If graph is submitted multiple times, dependencies are automatically added by the runtime to prevent concurrent executions of an identical graph.

Such usage results in multiple calls by the SYCL runtime to
`urEnqueueCommandBufferExp` with the same UR command-buffer and event
dependencies to prevent concurrent execution. Without support for
simultaneous-use the OpenCL adapter code cannot guarantee that the
first command-buffer submission has finished execution before it
makes following `clEnqueueCommandBufferKHR` calls with the `cl_event`
decencies. If the first submission is still executing, then an error
will be reported.

Workarounds like adding blocking host waits to the OpenCL UR adapter
are possible, but requiring simultaneous use reflects the vendor
requirements as they are for the currently implementation.

I've tried to document this all in the UR spec and SYCL-Graph design
docs, which also includes a couple of cleanups I found along the way.

Author: Ewan Crawford

sycl/doc/design/CommandGraph.md

@@ -28,30 +28,26 @@ document for details of support of different SYCL backends.
 ### UR Command-Buffer Experimental Feature
 
 The command-buffer concept has been introduced to UR as an
-[experimental feature](https://oneapi-src.github.io/unified-runtime/core/api.html#command-buffer-experimental)
-with the following entry-points:
-
-| Function                                     | Description |
-| -------------------------------------------- | ----------- |
-| `urCommandBufferCreateExp`                   | Create a command-buffer. |
-| `urCommandBufferRetainExp`                   | Incrementing reference count of command-buffer. |
-| `urCommandBufferReleaseExp`                  | Decrementing reference count of command-buffer. |
-| `urCommandBufferFinalizeExp`                 | No more commands can be appended, makes command-buffer ready to enqueue on a command-queue. |
-| `urCommandBufferAppendKernelLaunchExp`       | Append a kernel execution command to command-buffer. |
-| `urCommandBufferAppendUSMMemcpyExp`          | Append a USM memcpy command to the command-buffer. |
-| `urCommandBufferAppendUSMFillExp`            | Append a USM fill command to the command-buffer. |
-| `urCommandBufferAppendMemBufferCopyExp`      | Append a mem buffer copy command to the command-buffer. |
-| `urCommandBufferAppendMemBufferWriteExp`     | Append a memory write command to a command-buffer object. |
-| `urCommandBufferAppendMemBufferReadExp`      | Append a memory read command to a command-buffer object. |
-| `urCommandBufferAppendMemBufferCopyRectExp`  | Append a rectangular memory copy command to a command-buffer object. |
-| `urCommandBufferAppendMemBufferWriteRectExp` | Append a rectangular memory write command to a command-buffer object. |
-| `urCommandBufferAppendMemBufferReadRectExp`  | Append a rectangular memory read command to a command-buffer object. |
-| `urCommandBufferAppendMemBufferFillExp`      | Append a memory fill command to a command-buffer object. |
-| `urEnqueueCommandBufferExp`                  | Submit command-buffer to a command-queue for execution. |
-| `urCommandBufferUpdateKernelLaunchExp`       | Updates the parameters of a previous kernel launch command. |
-
+[experimental feature](https://oneapi-src.github.io/unified-runtime/core/api.html#command-buffer-experimental).
 See the [UR EXP-COMMAND-BUFFER](https://oneapi-src.github.io/unified-runtime/core/EXP-COMMAND-BUFFER.html)
-specification for more details.
+specification for details.
+
+Device support for SYCL-Graph is communicated to the user via two aspects.
+The `aspect::ext_oneapi_limited_graph` aspect for basic graph support and
+the `aspect::ext_oneapi_graph` aspect for full graph support.
+
+The `UR_DEVICE_INFO_COMMAND_BUFFER_SUPPORT_EXP` query result is used by the
+SYCL-RT to inform whether to report `aspect::ext_oneapi_limited_graph`.
+
+Reporting of the `aspect::ext_oneapi_graph` aspect is based on the
+`UR_DEVICE_INFO_COMMAND_BUFFER_UPDATE_CAPABILITIES_EXP` query result. For
+a device to report this aspect, the UR query must report support for all of:
+
+* `UR_DEVICE_COMMAND_BUFFER_UPDATE_CAPABILITY_FLAG_KERNEL_ARGUMENTS`
+* `UR_DEVICE_COMMAND_BUFFER_UPDATE_CAPABILITY_FLAG_LOCAL_WORK_SIZE`
+* `UR_DEVICE_COMMAND_BUFFER_UPDATE_CAPABILITY_FLAG_GLOBAL_WORK_SIZE`
+* `UR_DEVICE_COMMAND_BUFFER_UPDATE_CAPABILITY_FLAG_GLOBAL_WORK_OFFSET`
+* `UR_DEVICE_COMMAND_BUFFER_UPDATE_CAPABILITY_FLAG_KERNEL_HANDLE`
 
 ## Design
 
@@ -608,43 +604,14 @@ SYCL-Graph is only enabled for an OpenCL backend when the
 extension is available, however this information isn't available until runtime
 due to OpenCL implementations being loaded through an ICD.
 
-The `ur_exp_command_buffer` string is conditionally returned from the OpenCL
-command-buffer UR backend at runtime based on `cl_khr_command_buffer` support
-to indicate that the graph extension should be enabled. This is information
-is propagated to the SYCL user via the
-`device.get_info<info::device::graph_support>()` query for graph extension
-support.
-
-#### Limitations
-
-Due to the API mapping gaps documented in the following section, OpenCL as a
-SYCL backend cannot fully support the graph API. Instead, there are
-limitations in the types of nodes which a user can add to a graph, using
-an unsupported node type will cause a SYCL exception to be thrown in graph
-finalization with error code `sycl::errc::feature_not_supported` and a message
-mentioning the unsupported command. For example,
-
-```
-terminate called after throwing an instance of 'sycl::_V1::exception'
-what():  USM copy command not supported by graph backend
-```
-
-The types of commands which are unsupported, and lead to this exception are:
-* `handler::copy(src, dest)` - Where `src` is an accessor and `dest` is a pointer.
-   This corresponds to a memory buffer read command.
-* `handler::copy(src, dest)` - Where `src` is an pointer and `dest` is an accessor.
-  This corresponds to a memory buffer write command.
-* `handler::copy(src, dest)` or `handler::memcpy(dest, src)` - Where both `src` and
-   `dest` are USM pointers. This corresponds to a USM copy command.
-* `handler::fill(ptr, pattern, count)` - This corresponds to a USM memory
-  fill command.
-* `handler::memset(ptr, value, numBytes)` - This corresponds to a USM memory
-  fill command.
-* `handler::prefetch()`.
-* `handler::mem_advise()`.
-
-Note that `handler::copy(src, dest)` where both `src` and `dest` are an accessor
-is supported, as a memory buffer copy command exists in the OpenCL extension.
+The `UR_DEVICE_INFO_COMMAND_BUFFER_SUPPORT_EXP` UR query returns true in the
+OpenCL UR adapter based on
+the presence of `cl_khr_command_buffer`, and the OpenCL device reporting
+support for
+[CL_COMMAND_BUFFER_CAPABILITY_SIMULTANEOUS_USE_KHR](https://registry.khronos.org/OpenCL/specs/3.0-unified/html/OpenCL_API.html#CL_COMMAND_BUFFER_CAPABILITY_SIMULTANEOUS_USE_KHR).
+The later is required to enable multiple submissions of the same executable
+`command_graph` object without having to do a blocking wait on prior submissions
+in-between.
 
 #### UR API Mapping
 
@@ -678,18 +645,56 @@ adapter where there is matching support for each function in the list.
 |  | clGetCommandBufferInfoKHR | No |
 |  | clCommandSVMMemcpyKHR | No |
 |  | clCommandSVMMemFillKHR | No |
-| urCommandBufferUpdateKernelLaunchExp | clUpdateMutableCommandsKHR | Yes[1] |
+| urCommandBufferUpdateKernelLaunchExp | clUpdateMutableCommandsKHR | Partial [See Update Section](#update-support) |
 
 We are looking to address these gaps in the future so that SYCL-Graph can be
 fully supported on a `cl_khr_command_buffer` backend.
 
-[1] Support for `urCommandBufferUpdateKernelLaunchExp` used to update the
+#### Unsupported Command Types
+
+Due to the API mapping gaps documented in the previous section, OpenCL as a
+SYCL backend cannot fully support the graph API. Instead, there are
+limitations in the types of nodes which a user can add to a graph, using
+an unsupported node type will cause a SYCL exception to be thrown in graph
+finalization with error code `sycl::errc::feature_not_supported` and a message
+mentioning the unsupported command. For example,
+
+```
+terminate called after throwing an instance of 'sycl::_V1::exception'
+what():  USM copy command not supported by graph backend
+```
+
+The types of commands which are unsupported, and lead to this exception are:
+* `handler::copy(src, dest)` - Where `src` is an accessor and `dest` is a pointer.
+   This corresponds to a memory buffer read command.
+* `handler::copy(src, dest)` - Where `src` is an pointer and `dest` is an accessor.
+  This corresponds to a memory buffer write command.
+* `handler::copy(src, dest)` or `handler::memcpy(dest, src)` - Where both `src` and
+   `dest` are USM pointers. This corresponds to a USM copy command.
+* `handler::fill(ptr, pattern, count)` - This corresponds to a USM memory
+  fill command.
+* `handler::memset(ptr, value, numBytes)` - This corresponds to a USM memory
+  fill command.
+* `handler::prefetch()`.
+* `handler::mem_advise()`.
+
+Note that `handler::copy(src, dest)` where both `src` and `dest` are an accessor
+is supported, as a memory buffer copy command exists in the OpenCL extension.
+
+#### Update Support
+
+Support for `urCommandBufferUpdateKernelLaunchExp` used to update the
 configuration of kernel commands requires an OpenCL implementation with the
 [cl_khr_command_buffer_mutable_dispatch](https://registry.khronos.org/OpenCL/specs/3.0-unified/html/OpenCL_Ext.html#cl_khr_command_buffer_mutable_dispatch)
-extension. The optional capabilities that are reported by this extension must
-include all of of `CL_MUTABLE_DISPATCH_GLOBAL_OFFSET_KHR`,
-`CL_MUTABLE_DISPATCH_GLOBAL_SIZE_KHR`, `CL_MUTABLE_DISPATCH_LOCAL_SIZE_KHR`,
-`CL_MUTABLE_DISPATCH_ARGUMENTS_KHR`, and `CL_MUTABLE_DISPATCH_EXEC_INFO_KHR`.
+extension.
+
+However, the OpenCL adapter can not report `aspect::ext_oneapi_graph` for full
+SYCL-Graph support. As the `cl_khr_command_buffer_mutable_dispatch` extension
+has no concept of updating the `cl_kernel` objects in kernel commands, and so
+can't report the
+`UR_DEVICE_COMMAND_BUFFER_UPDATE_CAPABILITY_FLAG_KERNEL_HANDLE` capability.
+This extension limitation is tracked in by the OpenCL Working Group in an
+[OpenCL-Docs Issue](https://github.com/KhronosGroup/OpenCL-Docs/issues/1279).
 
 #### UR Command-Buffer Implementation
 

unified-runtime/scripts/core/EXP-COMMAND-BUFFER.rst

@@ -58,11 +58,11 @@ to provide additional properties for how the command-buffer should be
 constructed. The members defined in ${x}_exp_command_buffer_desc_t are:
 
 * ``isUpdatable``, which should be set to ``true`` to support :ref:`updating
-command-buffer commands`.
+  command-buffer commands`.
 * ``isInOrder``, which should be set to ``true`` to enable commands enqueued to
-a command-buffer to be executed in an in-order fashion where possible.
+  a command-buffer to be executed in an in-order fashion where possible.
 * ``enableProfiling``, which should be set to ``true`` to enable profiling of
-the command-buffer.
+  the command-buffer.
 
 Command-buffers are reference counted and can be retained and released by
 calling ${x}CommandBufferRetainExp and ${x}CommandBufferReleaseExp respectively.
@@ -226,15 +226,30 @@ Enqueueing Command-Buffers
 Command-buffers are submitted for execution on a ${x}_queue_handle_t with an
 optional list of dependent events. An event is returned which tracks the
 execution of the command-buffer, and will be complete when all appended commands
-have finished executing. It is adapter specific whether command-buffers can be
-enqueued or executed simultaneously, and submissions may be serialized.
+have finished executing.
 
 .. parsed-literal::
     ${x}_event_handle_t executionEvent;
-
     ${x}EnqueueCommandBufferExp(hQueue, hCommandBuffer, 0, nullptr,
                                 &executionEvent);
 
+A command-buffer can be submitted for execution while a previous submission
+of the same command-buffer is still awaiting completion. That is, the user is not
+required to do a blocking wait on the completion of the first command-buffer
+submission before making a second submission of the command-buffer.
+
+Submissions of the same command-buffer should be synchronized to prevent
+concurrent execution. For example, by using events, barriers, or in-order queue
+dependencies. The behavior of multiple submissions of the same command-buffer
+that can execute concurrently is undefined.
+
+.. parsed-literal::
+    // Valid usage if hQueue is in-order but undefined behavior is out-of-order
+    ${x}EnqueueCommandBufferExp(hQueue, hCommandBuffer, 0, nullptr,
+                                nullptr);
+    ${x}EnqueueCommandBufferExp(hQueue, hCommandBuffer, 0, nullptr,
+                                nullptr);
+
 
 Updating Command-Buffer Commands
 --------------------------------------------------------------------------------

unified-runtime/source/adapters/opencl/device.cpp

@@ -1524,9 +1524,19 @@ UR_APIEXPORT ur_result_t UR_APICALL urDeviceGetInfo(ur_device_handle_t hDevice,
     CL_RETURN_ON_FAILURE(clGetDeviceInfo(Dev, CL_DEVICE_EXTENSIONS, ExtSize,
                                          ExtStr.data(), nullptr));
 
-    std::string SupportedExtensions(ExtStr.c_str());
-    return ReturnValue(ExtStr.find("cl_khr_command_buffer") !=
-                       std::string::npos);
+    // cl_khr_command_buffer is required for UR command-buffer support
+    cl_device_command_buffer_capabilities_khr Caps = 0;
+    if (ExtStr.find("cl_khr_command_buffer") != std::string::npos) {
+      // A UR command-buffer user needs to be able to enqueue another
+      // submission of the same UR command-buffer without having to manually
+      // check if the first submission has completed.
+      CL_RETURN_ON_FAILURE(
+          clGetDeviceInfo(Dev, CL_DEVICE_COMMAND_BUFFER_CAPABILITIES_KHR,
+                          sizeof(Caps), &Caps, nullptr));
+    }
+
+    return ReturnValue(
+        0 != (Caps & CL_COMMAND_BUFFER_CAPABILITY_SIMULTANEOUS_USE_KHR));
   }
   case UR_DEVICE_INFO_COMMAND_BUFFER_UPDATE_CAPABILITIES_EXP: {
     cl_device_id Dev = cl_adapter::cast<cl_device_id>(hDevice);