[SYCL][DOC] Initial commit for queue priority extension

sycl/doc/extensions/proposed/sycl_ext_oneapi_queue_priority.asciidoc

@@ -0,0 +1,119 @@
+= sycl_ext_oneapi_queue_priority
+
+:source-highlighter: coderay
+:coderay-linenums-mode: table
+
+// This section needs to be after the document title.
+:doctype: book
+:toc2:
+:toc: left
+:encoding: utf-8
+:lang: en
+:dpcpp: pass:[DPC++]
+
+// Set the default source code type in this document to C++,
+// for syntax highlighting purposes.  This is needed because
+// docbook uses c++ and html5 uses cpp.
+:language: {basebackend@docbook:c++:cpp}
+
+
+== Notice
+
+[%hardbreaks]
+Copyright (C) 2022-2023 Intel Corporation.  All rights reserved.
+
+Khronos(R) is a registered trademark and SYCL(TM) and SPIR(TM) are trademarks
+of The Khronos Group Inc.  OpenCL(TM) is a trademark of Apple Inc. used by
+permission by Khronos.
+
+
+== Contact
+
+To report problems with this extension, please open a new issue at:
+
+https://github.com/intel/llvm/issues
+
+
+== Dependencies
+
+This extension is written against the SYCL 2020 revision 6 specification.  All
+references below to the "core SYCL specification" or to section numbers in the
+SYCL specification refer to that revision.
+
+== Status
+
+This is a proposed extension specification, intended to gather community
+feedback.  Interfaces defined in this specification may not be implemented yet
+or may be in a preliminary state.  The specification itself may also change in
+incompatible ways before it is finalized.  *Shipping software products should
+not rely on APIs defined in this specification.*
+
+== Specification
+
+This extension defines an additional queue property that permit a backend,
+when supported, to create command queues with different levels of priority.
+Priorities are hints from the programmer that certain command submissions 
+to a device may execute before others of lesser priority.
+
+=== Feature test macro
+
+This extension provides a feature-test macro as described in the core SYCL
+specification.  An implementation supporting this extension must predefine the
+macro `SYCL_EXT_ONEAPI_QUEUE_PRIORITY` to one of the values defined in the table
+below.  Applications can test for the existence of this macro to determine if
+the implementation supports this feature, or applications can test the macro's
+value to determine which of the extension's features the implementation
+supports.
+
+[%header,cols="1,5"]
+|===
+|Value
+|Description
+
+|1
+|Initial version of this extension.
+|===
+
+=== API Additions
+
+
+This extension defines the following new property that may be passed to the 
+constructor of the `queue` class:
+
+[%header,cols="1,5"]
+|===
+|Property
+|Description
+
+| `sycl::ext::oneapi::property::queue::priority`
+|
+|===
+
+[%header,cols="1,5"]
+|===
+|Property Constructor
+|Description
+
+| `sycl::ext::oneapi::property::queue::priority(int priority=0)`
+|  Specifies that the queue should be constructed with the specified `priority`.
+Commands executed by this queue may take priority over commands with lower priority
+on this queue's device. The default priority has value `0`. If the user specifies
+`priority` outside the range returned by `sycl::ext::oneapi::queue::priority_range`,
+`priority` will be clamped down or up to the least or greatest priority in the range.
+
+|===
+
+This extension also defines the following new query for the `queue` class:
+
+[%header,cols="1,5"]
+|===
+|Property
+|Description
+
+| `sycl::ext::oneapi::info::queue::priority_range`
+| Returns a `std::array<int,2>` that represents the `{leastPriority,greatestPriority}`
+for this queue. Lower numbers imply greater priorities. The default priority has value `0`.
+Specifying priorities outside of this range when creating a queue will result in the specified
+priority being clamped down or up to the least priority or greatest priority, respectively.
+
+|===