[UR][Offload] Event waiting

Implement urEventsWait[WithBarrier] and respect the waitlist of enqueue
functions.

Author: RossBrunton

unified-runtime/source/adapters/offload/enqueue.cpp

@@ -19,16 +19,126 @@
 #include "queue.hpp"
 #include "ur2offload.hpp"
 
+namespace {
+ol_result_t waitOnEvents(ol_queue_handle_t Queue,
+                         const ur_event_handle_t *UrEvents, size_t NumEvents) {
+  if (NumEvents) {
+    std::vector<ol_event_handle_t> OlEvents;
+    OlEvents.reserve(NumEvents);
+    for (size_t I = 0; I < NumEvents; I++) {
+      OlEvents.push_back(UrEvents[I]->OffloadEvent);
+    }
+
+    olWaitEvents(Queue, OlEvents.data(), NumEvents);
+  }
+  return nullptr;
+}
+
+ol_result_t makeEvent(ur_command_t Type, ol_queue_handle_t OlQueue,
+                      ur_queue_handle_t UrQueue, ur_event_handle_t *UrEvent) {
+  if (UrEvent) {
+    auto *Event = new ur_event_handle_t_(Type, UrQueue);
+    if (auto Res = olCreateEvent(OlQueue, &Event->OffloadEvent)) {
+      delete Event;
+      return Res;
+    };
+    *UrEvent = Event;
+  }
+  return nullptr;
+}
+
+template <bool Barrier>
+ur_result_t doWait(ur_queue_handle_t hQueue, uint32_t numEventsInWaitList,
+                   const ur_event_handle_t *phEventWaitList,
+                   ur_event_handle_t *phEvent) {
+  constexpr ur_command_t TYPE =
+      Barrier ? UR_COMMAND_EVENTS_WAIT_WITH_BARRIER : UR_COMMAND_EVENTS_WAIT;
+  ol_queue_handle_t TargetQueue;
+  if (!numEventsInWaitList && hQueue->isInOrder()) {
+    // In order queue so all work is done in submission order, so it's a
+    // no-op
+    if (phEvent) {
+      OL_RETURN_ON_ERR(hQueue->nextQueue(TargetQueue));
+      OL_RETURN_ON_ERR(makeEvent(TYPE, TargetQueue, hQueue, phEvent));
+    }
+    return UR_RESULT_SUCCESS;
+  }
+  OL_RETURN_ON_ERR(hQueue->nextQueue(TargetQueue));
+
+  if (!numEventsInWaitList) {
+    // "If the event list is empty, it waits for all previously enqueued
+    // commands to complete."
+
+    // Create events on each active queue for an arbitrary thread to block on
+    // TODO: Can we efficiently check if each thread is "finished" rather than
+    // creating an event?
+    std::vector<ol_event_handle_t> OffloadHandles{};
+    for (auto *Q : hQueue->OffloadQueues) {
+      if (Q == nullptr) {
+        break;
+      }
+      if (Q == TargetQueue) {
+        continue;
+      }
+      OL_RETURN_ON_ERR(olCreateEvent(Q, &OffloadHandles.emplace_back()));
+    }
+    OL_RETURN_ON_ERR(olWaitEvents(TargetQueue, OffloadHandles.data(),
+                                  OffloadHandles.size()));
+  } else {
+    OL_RETURN_ON_ERR(
+        waitOnEvents(TargetQueue, phEventWaitList, numEventsInWaitList));
+  }
+
+  OL_RETURN_ON_ERR(makeEvent(TYPE, TargetQueue, hQueue, phEvent));
+
+  if constexpr (Barrier) {
+    ol_event_handle_t BarrierEvent;
+    if (phEvent) {
+      BarrierEvent = (*phEvent)->OffloadEvent;
+    } else {
+      OL_RETURN_ON_ERR(olCreateEvent(TargetQueue, &BarrierEvent));
+    }
+
+    // Ensure any newly created work waits on this barrier
+    hQueue->Barrier.store(BarrierEvent);
+
+    // Block all existing threads on the barrier
+    for (auto *Q : hQueue->OffloadQueues) {
+      if (Q == nullptr) {
+        break;
+      }
+      if (Q == TargetQueue) {
+        continue;
+      }
+      OL_RETURN_ON_ERR(olWaitEvents(Q, &BarrierEvent, 1));
+    }
+  }
+
+  return UR_RESULT_SUCCESS;
+}
+} // namespace
+
+UR_APIEXPORT ur_result_t UR_APICALL urEnqueueEventsWait(
+    ur_queue_handle_t hQueue, uint32_t numEventsInWaitList,
+    const ur_event_handle_t *phEventWaitList, ur_event_handle_t *phEvent) {
+  return doWait<false>(hQueue, numEventsInWaitList, phEventWaitList, phEvent);
+}
+
+UR_APIEXPORT ur_result_t UR_APICALL urEnqueueEventsWaitWithBarrier(
+    ur_queue_handle_t hQueue, uint32_t numEventsInWaitList,
+    const ur_event_handle_t *phEventWaitList, ur_event_handle_t *phEvent) {
+  return doWait<true>(hQueue, numEventsInWaitList, phEventWaitList, phEvent);
+}
+
 UR_APIEXPORT ur_result_t UR_APICALL urEnqueueKernelLaunch(
     ur_queue_handle_t hQueue, ur_kernel_handle_t hKernel, uint32_t workDim,
     const size_t *pGlobalWorkOffset, const size_t *pGlobalWorkSize,
     const size_t *pLocalWorkSize, uint32_t, const ur_kernel_launch_property_t *,
     uint32_t numEventsInWaitList, const ur_event_handle_t *phEventWaitList,
     ur_event_handle_t *phEvent) {
-  // Ignore wait list for now
-  (void)numEventsInWaitList;
-  (void)phEventWaitList;
-  //
+  ol_queue_handle_t Queue;
+  OL_RETURN_ON_ERR(hQueue->nextQueue(Queue));
+  OL_RETURN_ON_ERR(waitOnEvents(Queue, phEventWaitList, numEventsInWaitList));
 
   (void)pGlobalWorkOffset;
 
@@ -67,20 +177,11 @@ UR_APIEXPORT ur_result_t UR_APICALL urEnqueueKernelLaunch(
   LaunchArgs.GroupSize.z = GroupSize[2];
   LaunchArgs.DynSharedMemory = 0;
 
-  ol_queue_handle_t Queue;
-  OL_RETURN_ON_ERR(hQueue->nextQueue(Queue));
   OL_RETURN_ON_ERR(olLaunchKernel(
       Queue, hQueue->OffloadDevice, hKernel->OffloadKernel,
       hKernel->Args.getStorage(), hKernel->Args.getStorageSize(), &LaunchArgs));
 
-  if (phEvent) {
-    auto *Event = new ur_event_handle_t_(UR_COMMAND_KERNEL_LAUNCH, hQueue);
-    if (auto Res = olCreateEvent(Queue, &Event->OffloadEvent)) {
-      delete Event;
-      return offloadResultToUR(Res);
-    };
-    *phEvent = Event;
-  }
+  OL_RETURN_ON_ERR(makeEvent(UR_COMMAND_KERNEL_LAUNCH, Queue, hQueue, phEvent));
   return UR_RESULT_SUCCESS;
 }
 
@@ -103,10 +204,9 @@ ur_result_t doMemcpy(ur_command_t Command, ur_queue_handle_t hQueue,
                      size_t size, bool blocking, uint32_t numEventsInWaitList,
                      const ur_event_handle_t *phEventWaitList,
                      ur_event_handle_t *phEvent) {
-  // Ignore wait list for now
-  (void)numEventsInWaitList;
-  (void)phEventWaitList;
-  //
+  ol_queue_handle_t Queue;
+  OL_RETURN_ON_ERR(hQueue->nextQueue(Queue));
+  OL_RETURN_ON_ERR(waitOnEvents(Queue, phEventWaitList, numEventsInWaitList));
 
   if (blocking) {
     OL_RETURN_ON_ERR(
@@ -117,8 +217,6 @@ ur_result_t doMemcpy(ur_command_t Command, ur_queue_handle_t hQueue,
     return UR_RESULT_SUCCESS;
   }
 
-  ol_queue_handle_t Queue;
-  OL_RETURN_ON_ERR(hQueue->nextQueue(Queue));
   OL_RETURN_ON_ERR(
       olMemcpy(Queue, DestPtr, DestDevice, SrcPtr, SrcDevice, size));
   if (phEvent) {
@@ -192,17 +290,6 @@ UR_APIEXPORT ur_result_t UR_APICALL urEnqueueDeviceGlobalVariableWrite(
                   numEventsInWaitList, phEventWaitList, phEvent);
 }
 
-ur_result_t enqueueNoOp(ur_command_t Type, ur_queue_handle_t hQueue,
-                        ur_event_handle_t *phEvent) {
-  // This path is a no-op, but we can't output a real event because
-  // Offload doesn't currently support creating arbitrary events, and we
-  // don't know the last real event in the queue. Instead we just have to
-  // wait on the whole queue and then return an empty (implicitly
-  // finished) event.
-  *phEvent = ur_event_handle_t_::createEmptyEvent(Type, hQueue);
-  return urQueueFinish(hQueue);
-}
-
 UR_APIEXPORT ur_result_t UR_APICALL urEnqueueMemBufferMap(
     ur_queue_handle_t hQueue, ur_mem_handle_t hBuffer, bool blockingMap,
     ur_map_flags_t mapFlags, size_t offset, size_t size,
@@ -226,15 +313,16 @@ UR_APIEXPORT ur_result_t UR_APICALL urEnqueueMemBufferMap(
     Result = urEnqueueMemBufferRead(hQueue, hBuffer, blockingMap, offset, size,
                                     MapPtr, numEventsInWaitList,
                                     phEventWaitList, phEvent);
-  } else {
-    if (IsPinned) {
-      // TODO: Ignore the event waits list for now. When urEnqueueEventsWait is
-      // implemented we can call it on the wait list.
-    }
-
-    if (phEvent) {
-      enqueueNoOp(UR_COMMAND_MEM_BUFFER_MAP, hQueue, phEvent);
+  } else if (numEventsInWaitList || phEvent) {
+    ol_queue_handle_t Queue;
+    OL_RETURN_ON_ERR(hQueue->nextQueue(Queue));
+    if ((!hQueue->isInOrder() && phEvent) || hQueue->isInOrder()) {
+      // Out-of-order queues running no-op work only have side effects if there
+      // is an output event
+      waitOnEvents(Queue, phEventWaitList, numEventsInWaitList);
     }
+    OL_RETURN_ON_ERR(
+        makeEvent(UR_COMMAND_MEM_BUFFER_MAP, Queue, hQueue, phEvent));
   }
   *ppRetMap = MapPtr;
 
@@ -260,15 +348,15 @@ UR_APIEXPORT ur_result_t UR_APICALL urEnqueueMemUnmap(
     Result = urEnqueueMemBufferWrite(
         hQueue, hMem, true, Map->MapOffset, Map->MapSize, pMappedPtr,
         numEventsInWaitList, phEventWaitList, phEvent);
-  } else {
-    if (IsPinned) {
-      // TODO: Ignore the event waits list for now. When urEnqueueEventsWait is
-      // implemented we can call it on the wait list.
-    }
-
-    if (phEvent) {
-      enqueueNoOp(UR_COMMAND_MEM_UNMAP, hQueue, phEvent);
+  } else if (numEventsInWaitList || phEvent) {
+    ol_queue_handle_t Queue;
+    OL_RETURN_ON_ERR(hQueue->nextQueue(Queue));
+    if ((!hQueue->isInOrder() && phEvent) || hQueue->isInOrder()) {
+      // Out-of-order queues running no-op work only have side effects if there
+      // is an output event
+      waitOnEvents(Queue, phEventWaitList, numEventsInWaitList);
     }
+    OL_RETURN_ON_ERR(makeEvent(UR_COMMAND_MEM_UNMAP, Queue, hQueue, phEvent));
   }
   BufferImpl.unmap(pMappedPtr);
 

unified-runtime/source/adapters/offload/queue.hpp

@@ -23,8 +23,8 @@ struct ur_queue_handle_t_ : RefCounted {
       : OffloadQueues((Flags & UR_QUEUE_FLAG_OUT_OF_ORDER_EXEC_MODE_ENABLE)
                           ? 1
                           : OOO_QUEUE_POOL_SIZE),
-        QueueOffset(0), OffloadDevice(Device), UrContext(UrContext),
-        Flags(Flags) {}
+        QueueOffset(0), Barrier(nullptr), OffloadDevice(Device),
+        UrContext(UrContext), Flags(Flags) {}
 
   // In-order queues only have one element here, while out of order queues have
   // a bank of queues to use. We rotate through them round robin instead of
@@ -35,19 +35,27 @@ struct ur_queue_handle_t_ : RefCounted {
   // `stream_queue_t`. In the future, if we want more performance or it
   // simplifies the implementation of a feature, we can consider using it.
   std::vector<ol_queue_handle_t> OffloadQueues;
-  size_t QueueOffset;
+  std::atomic<size_t> QueueOffset;
+  std::atomic<ol_event_handle_t> Barrier;
   ol_device_handle_t OffloadDevice;
   ur_context_handle_t UrContext;
   ur_queue_flags_t Flags;
 
+  bool isInOrder() const { return OffloadQueues.size() == 1; }
+
   ol_result_t nextQueue(ol_queue_handle_t &Handle) {
-    auto &Slot = OffloadQueues[QueueOffset++];
-    QueueOffset %= OffloadQueues.size();
+    auto &Slot = OffloadQueues[(QueueOffset++) % OffloadQueues.size()];
 
     if (!Slot) {
       if (auto Res = olCreateQueue(OffloadDevice, &Slot)) {
         return Res;
       }
+
+      if (auto Event = Barrier.load()) {
+        if (auto Res = olWaitEvents(Slot, &Event, 1)) {
+          return Res;
+        }
+      }
     }
 
     Handle = Slot;

unified-runtime/source/adapters/offload/ur_interface_loader.cpp

@@ -170,8 +170,8 @@ UR_DLLEXPORT ur_result_t UR_APICALL urGetEnqueueProcAddrTable(
   }
   pDdiTable->pfnDeviceGlobalVariableRead = urEnqueueDeviceGlobalVariableRead;
   pDdiTable->pfnDeviceGlobalVariableWrite = urEnqueueDeviceGlobalVariableWrite;
-  pDdiTable->pfnEventsWait = nullptr;
-  pDdiTable->pfnEventsWaitWithBarrier = nullptr;
+  pDdiTable->pfnEventsWait = urEnqueueEventsWait;
+  pDdiTable->pfnEventsWaitWithBarrier = urEnqueueEventsWaitWithBarrier;
   pDdiTable->pfnKernelLaunch = urEnqueueKernelLaunch;
   pDdiTable->pfnMemBufferCopy = nullptr;
   pDdiTable->pfnMemBufferCopyRect = nullptr;