[SYCL][Docs] Add and implement in-order queue event extension (#12331)

This commit adds the extension for and implementation of the ability to get the last event of an in-order queue as well as setting an external event to be used as a dependence in an in-order queue. --------- Signed-off-by: Larsen, Steffen <steffen.larsen@intel.com>
intel · Jan 15, 2024 · 1907275 · 1907275
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diff --git a/sycl/doc/extensions/experimental/sycl_ext_oneapi_in_order_queue_events.asciidoc b/sycl/doc/extensions/experimental/sycl_ext_oneapi_in_order_queue_events.asciidoc
@@ -0,0 +1,151 @@
+= sycl_ext_oneapi_in_order_queue_events
+
+: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) 2024-2024 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 8 specification.  All
+references below to the "core SYCL specification" or to section numbers in the
+SYCL specification refer to that revision.
+
+
+== Status
+
+This is an experimental extension specification, intended to provide early
+access to features and gather community feedback.  Interfaces defined in this
+specification are implemented in {dpcpp}, but they are not finalized and may
+change incompatibly in future versions of {dpcpp} without prior notice.
+*Shipping software products should not rely on APIs defined in this
+specification.*
+
+
+== Overview
+
+SYCL 2020 in-order queues allow for simple control of submission ordering, i.e.
+commands are executed in the order they are submitted. This extension adds two
+additional APIs for controlling in-order queues: Getting the event from the last
+command submission into the queue and setting an external event as an implicit
+dependence on the next command submitted to the queue.
+
+This extension exists to solve a specific problem, and a general solution is
+still being evaluated.  It is not recommended for general usage.
+
+
+== Specification
+
+=== 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_IN_ORDER_QUEUE_EVENTS` 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
+|The APIs of this experimental extension are not versioned, so the
+ feature-test macro always has this value.
+|===
+
+=== New SYCL queue APIs
+
+This extension adds the following new APIs to the existing `sycl::queue` class:
+
+[source, c++]
+----
+namespace sycl {
+
+class queue {
+  ...
+
+  event ext_oneapi_get_last_event() const { /*...*/ }
+
+  void ext_oneapi_set_external_event(const event &external_event) { /*...*/ }
+}
+
+} // namespace sycl
+----
+
+These new APIs have the following behaviour:
+
+--
+[options="header"]
+|====
+| Function Definition | Description
+a| 
+[source, c++]
+----
+event ext_oneapi_get_last_event() const;
+----
+| Returns an event representing the execution of the last command submitted to
+the queue.
+
+Calls to this member function throw a `sycl::exception` with `errc::invalid` if
+the queue does not have the `property::queue::in_order` property.
+
+Calls to this member function throw a `sycl::exception` with `errc::invalid` if
+the queue has the `ext::oneapi::property::queue::discard_events` property from
+the
+link:../supported/sycl_ext_oneapi_discard_queue_events.asciidoc[sycl_ext_oneapi_discard_queue_events extension].
+
+a| 
+[source, c++]
+----
+void ext_oneapi_set_external_event(const event &externalEvent);
+----
+| Sets an event to be used as an additional dependency of the next command
+submission to the queue. Subsequent calls to this function will overwrite the
+event of the previous call, resulting in only the `externalEvent` from the last
+call to this function being a dependency of the next command submission.
+
+This is equivalent to calling `handler::depends_on()` in a command submission
+with the `externalEvent` from the most recent call to this member function since
+the previous command submission to the same queue.
+
+Calls to this member function throw a `sycl::exception` with `errc::invalid` if
+the queue does not have the `property::queue::in_order` property.
+
+Calls to this member function throw a `sycl::exception` with `errc::invalid` if
+the queue has the `ext::oneapi::property::queue::discard_events` property from
+the
+link:../supported/sycl_ext_oneapi_discard_queue_events.asciidoc[sycl_ext_oneapi_discard_queue_events extension].
+|====
+--
diff --git a/sycl/include/sycl/queue.hpp b/sycl/include/sycl/queue.hpp
@@ -2783,6 +2783,10 @@ class __SYCL_EXPORT queue : public detail::OwnerLessBase<queue> {
 
   pi_native_handle getNative(int32_t &NativeHandleDesc) const;
 
+  event ext_oneapi_get_last_event() const;
+
+  void ext_oneapi_set_external_event(const event &external_event);
+
 private:
   std::shared_ptr<detail::queue_impl> impl;
   queue(std::shared_ptr<detail::queue_impl> impl) : impl(impl) {}

diff --git a/sycl/source/detail/queue_impl.cpp b/sycl/source/detail/queue_impl.cpp
@@ -61,6 +61,20 @@ static event createDiscardedEvent() {
   return createSyclObjFromImpl<event>(EventImpl);
 }
 
+const std::vector<event> &
+queue_impl::getExtendDependencyList(const std::vector<event> &DepEvents,
+                                    std::vector<event> &MutableVec) {
+  if (isInOrder()) {
+    std::optional<event> ExternalEvent = popExternalEvent();
+    if (ExternalEvent) {
+      MutableVec = DepEvents;
+      MutableVec.push_back(*ExternalEvent);
+      return MutableVec;
+    }
+  }
+  return DepEvents;
+}
+
 event queue_impl::memset(const std::shared_ptr<detail::queue_impl> &Self,
                          void *Ptr, int Value, size_t Count,
                          const std::vector<event> &DepEvents) {
@@ -108,9 +122,13 @@ event queue_impl::memset(const std::shared_ptr<detail::queue_impl> &Self,
     if (isInOrder() && MLastCGType == CG::CGTYPE::CodeplayHostTask)
       MLastEvent.wait();
 
+    std::vector<event> MutableDepEvents;
+    const std::vector<event> &ExpandedDepEvents =
+        getExtendDependencyList(DepEvents, MutableDepEvents);
+
     auto EventImpl = detail::getSyclObjImpl(ResEvent);
     MemoryManager::fill_usm(Ptr, Self, Count, Value,
-                            getOrWaitEvents(DepEvents, MContext),
+                            getOrWaitEvents(ExpandedDepEvents, MContext),
                             &EventImpl->getHandleRef(), EventImpl);
 
     if (MContext->is_host())
@@ -201,9 +219,13 @@ event queue_impl::memcpy(const std::shared_ptr<detail::queue_impl> &Self,
     if (isInOrder() && MLastCGType == CG::CGTYPE::CodeplayHostTask)
       MLastEvent.wait();
 
+    std::vector<event> MutableDepEvents;
+    const std::vector<event> &ExpandedDepEvents =
+        getExtendDependencyList(DepEvents, MutableDepEvents);
+
     auto EventImpl = detail::getSyclObjImpl(ResEvent);
     MemoryManager::copy_usm(Src, Self, Count, Dest,
-                            getOrWaitEvents(DepEvents, MContext),
+                            getOrWaitEvents(ExpandedDepEvents, MContext),
                             &EventImpl->getHandleRef(), EventImpl);
 
     if (MContext->is_host())
@@ -244,9 +266,13 @@ event queue_impl::mem_advise(const std::shared_ptr<detail::queue_impl> &Self,
     if (isInOrder() && MLastCGType == CG::CGTYPE::CodeplayHostTask)
       MLastEvent.wait();
 
+    std::vector<event> MutableDepEvents;
+    const std::vector<event> &ExpandedDepEvents =
+        getExtendDependencyList(DepEvents, MutableDepEvents);
+
     auto EventImpl = detail::getSyclObjImpl(ResEvent);
     MemoryManager::advise_usm(Ptr, Self, Length, Advice,
-                              getOrWaitEvents(DepEvents, MContext),
+                              getOrWaitEvents(ExpandedDepEvents, MContext),
                               &EventImpl->getHandleRef(), EventImpl);
 
     if (MContext->is_host())
@@ -288,11 +314,15 @@ event queue_impl::memcpyToDeviceGlobal(
     if (isInOrder() && MLastCGType == CG::CGTYPE::CodeplayHostTask)
       MLastEvent.wait();
 
+    std::vector<event> MutableDepEvents;
+    const std::vector<event> &ExpandedDepEvents =
+        getExtendDependencyList(DepEvents, MutableDepEvents);
+
     auto EventImpl = detail::getSyclObjImpl(ResEvent);
-    MemoryManager::copy_to_device_global(DeviceGlobalPtr, IsDeviceImageScope,
-                                         Self, NumBytes, Offset, Src,
-                                         getOrWaitEvents(DepEvents, MContext),
-                                         &EventImpl->getHandleRef(), EventImpl);
+    MemoryManager::copy_to_device_global(
+        DeviceGlobalPtr, IsDeviceImageScope, Self, NumBytes, Offset, Src,
+        getOrWaitEvents(ExpandedDepEvents, MContext),
+        &EventImpl->getHandleRef(), EventImpl);
 
     if (MContext->is_host())
       return MDiscardEvents ? createDiscardedEvent() : event();
@@ -333,11 +363,15 @@ event queue_impl::memcpyFromDeviceGlobal(
     if (isInOrder() && MLastCGType == CG::CGTYPE::CodeplayHostTask)
       MLastEvent.wait();
 
+    std::vector<event> MutableDepEvents;
+    const std::vector<event> &ExpandedDepEvents =
+        getExtendDependencyList(DepEvents, MutableDepEvents);
+
     auto EventImpl = detail::getSyclObjImpl(ResEvent);
     MemoryManager::copy_from_device_global(
         DeviceGlobalPtr, IsDeviceImageScope, Self, NumBytes, Offset, Dest,
-        getOrWaitEvents(DepEvents, MContext), &EventImpl->getHandleRef(),
-        EventImpl);
+        getOrWaitEvents(ExpandedDepEvents, MContext),
+        &EventImpl->getHandleRef(), EventImpl);
 
     if (MContext->is_host())
       return MDiscardEvents ? createDiscardedEvent() : event();

diff --git a/sycl/source/detail/queue_impl.hpp b/sycl/source/detail/queue_impl.hpp
@@ -716,6 +716,22 @@ class queue_impl {
 
   unsigned long long getQueueID() { return MQueueID; }
 
+  void setExternalEvent(const event &Event) {
+    std::lock_guard<std::mutex> Lock(MInOrderExternalEventMtx);
+    MInOrderExternalEvent = Event;
+  }
+
+  std::optional<event> popExternalEvent() {
+    std::lock_guard<std::mutex> Lock(MInOrderExternalEventMtx);
+    std::optional<event> Result = std::nullopt;
+    std::swap(Result, MInOrderExternalEvent);
+    return Result;
+  }
+
+  const std::vector<event> &
+  getExtendDependencyList(const std::vector<event> &DepEvents,
+                          std::vector<event> &MutableVec);
+
 protected:
   // Hook to the scheduler to clean up any fusion command held on destruction.
   void cleanup_fusion_cmd();
@@ -731,8 +747,8 @@ class queue_impl {
       };
 
       // Accessing and changing of an event isn't atomic operation.
-      // Hence, here is the lock for thread-safety.
-      std::lock_guard<std::mutex> Lock{MLastEventMtx};
+      // Hence, here is are locks for thread-safety.
+      std::lock_guard<std::mutex> LastEventLock{MLastEventMtx};
 
       if (MLastCGType == CG::CGTYPE::None)
         MLastCGType = Type;
@@ -744,6 +760,13 @@ class queue_impl {
       if (NeedSeparateDependencyMgmt)
         Handler.depends_on(MLastEvent);
 
+      // If there is an external event set, add it as a dependency and clear it.
+      // We do not need to hold the lock as MLastEventMtx will ensure the last
+      // event reflects the corresponding external event dependence as well.
+      std::optional<event> ExternalEvent = popExternalEvent();
+      if (ExternalEvent)
+        Handler.depends_on(*ExternalEvent);
+
       EventRet = Handler.finalize();
 
       MLastEvent = EventRet;
@@ -894,6 +917,13 @@ class queue_impl {
   // the fallback implementation of profiling info
   bool MFallbackProfiling = false;
 
+  // This event can be optionally provided by users for in-order queues to add
+  // an additional dependency for the subsequent submission in to the queue.
+  // Access to the event should be guarded with MInOrderExternalEventMtx.
+  // NOTE: std::optional must not be exposed in the ABI.
+  std::optional<event> MInOrderExternalEvent;
+  mutable std::mutex MInOrderExternalEventMtx;
+
 public:
   // Queue constructed with the discard_events property
   const bool MDiscardEvents;

diff --git a/sycl/source/feature_test.hpp.in b/sycl/source/feature_test.hpp.in
@@ -97,6 +97,7 @@ inline namespace _V1 {
 #define SYCL_EXT_INTEL_CACHE_CONTROLS 1
 #define SYCL_EXT_INTEL_FP_CONTROL 1
 #define SYCL_EXT_ONEAPI_NON_UNIFORM_GROUPS 1
+#define SYCL_EXT_ONEAPI_IN_ORDER_QUEUE_EVENTS 1
 
 #ifndef __has_include
 #define __has_include(x) 0

diff --git a/sycl/source/queue.cpp b/sycl/source/queue.cpp
@@ -300,5 +300,31 @@ bool queue::ext_codeplay_supports_fusion() const {
       ext::codeplay::experimental::property::queue::enable_fusion>();
 }
 
+event queue::ext_oneapi_get_last_event() const {
+  if (!is_in_order())
+    throw sycl::exception(
+        make_error_code(errc::invalid),
+        "ext_oneapi_get_last_event() can only be called on in-order queues.");
+  if (impl->MDiscardEvents)
+    throw sycl::exception(
+        make_error_code(errc::invalid),
+        "ext_oneapi_get_last_event() cannot be called on queues with the "
+        "ext::oneapi::property::queue::discard_events property.");
+  return impl->getLastEvent();
+}
+
+void queue::ext_oneapi_set_external_event(const event &external_event) {
+  if (!is_in_order())
+    throw sycl::exception(make_error_code(errc::invalid),
+                          "ext_oneapi_set_external_event() can only be called "
+                          "on in-order queues.");
+  if (impl->MDiscardEvents)
+    throw sycl::exception(
+        make_error_code(errc::invalid),
+        "ext_oneapi_set_external_event() cannot be called on queues with the "
+        "ext::oneapi::property::queue::discard_events property.");
+  return impl->setExternalEvent(external_event);
+}
+
 } // namespace _V1
 } // namespace sycl