[Offload] Verify SyncCycle for events in AMDGPU

[RossBrunton]

This check ensures that events after a synchronise (and thus after the
queue is reset) are always considered complete. A test has been added
as well.

[llvmbot]

@llvm/pr-subscribers-offload

@llvm/pr-subscribers-backend-amdgpu

Author: Ross Brunton (RossBrunton)

Changes

This check ensures that events after a synchronise (and thus after the
queue is reset) are always considered complete. A test has been added
as well.

---

Full diff: https://github.com/llvm/llvm-project/pull/149524.diff

2 Files Affected:

• (modified) offload/plugins-nextgen/amdgpu/src/rtl.cpp (+5)
• (modified) offload/unittests/OffloadAPI/event/olWaitEvent.cpp (+17)

diff --git a/offload/plugins-nextgen/amdgpu/src/rtl.cpp b/offload/plugins-nextgen/amdgpu/src/rtl.cpp
index d4400547f9568..f8db9bf0ae739 100644
--- a/offload/plugins-nextgen/amdgpu/src/rtl.cpp
+++ b/offload/plugins-nextgen/amdgpu/src/rtl.cpp
@@ -1665,6 +1665,11 @@ Error AMDGPUStreamTy::waitEvent(const AMDGPUEventTy &Event) {
 Error AMDGPUStreamTy::synchronizeOn(AMDGPUEventTy &Event) {
   std::lock_guard<std::mutex> Lock(Mutex);
 
+  // If this event was for an older sync cycle, it has already been finalized
+  if (Event.RecordedSyncCycle < SyncCycle)
+    return Plugin::success();
+  assert(Event.RecordedSyncCycle == SyncCycle && "event is from the future?");
+
   // Wait until the requested slot has completed
   if (auto Err = Slots[Event.RecordedSlot].Signal->wait(
           StreamBusyWaitMicroseconds, &Device))
diff --git a/offload/unittests/OffloadAPI/event/olWaitEvent.cpp b/offload/unittests/OffloadAPI/event/olWaitEvent.cpp
index f80dabb4fc93f..1f2977eda64e2 100644
--- a/offload/unittests/OffloadAPI/event/olWaitEvent.cpp
+++ b/offload/unittests/OffloadAPI/event/olWaitEvent.cpp
@@ -30,3 +30,20 @@ TEST_P(olWaitEventTest, Success) {
 TEST_P(olWaitEventTest, InvalidNullEvent) {
   ASSERT_ERROR(OL_ERRC_INVALID_NULL_HANDLE, olWaitEvent(nullptr));
 }
+
+TEST_P(olWaitEventTest, SuccessMultipleWait) {
+  uint32_t Src = 42;
+  void *DstPtr;
+
+  ol_event_handle_t Event = nullptr;
+  ASSERT_SUCCESS(
+      olMemAlloc(Device, OL_ALLOC_TYPE_DEVICE, sizeof(uint32_t), &DstPtr));
+  ASSERT_SUCCESS(
+      olMemcpy(Queue, DstPtr, Device, &Src, Host, sizeof(Src), &Event));
+  ASSERT_NE(Event, nullptr);
+
+  for (size_t I = 0; I < 10; I++)
+    ASSERT_SUCCESS(olWaitEvent(Event));
+
+  ASSERT_SUCCESS(olDestroyEvent(Event));
+}

[jhuber6]

So, this is if the user consumes an event twice?

[RossBrunton]

That, or if a later event gets consumed before an earlier one. If the latest event in the queue is synced on, the queue is reset and SyncCycle incremented.