D3D12: Optionally prevent StreamBuffer from executing command list

This applies to callers that do not have full knowledge of the command
list state, and thus, cannot restore it should allocations cause command
list execution. Instead we reallocate a new buffer. Should not happen
often enough for this to be a concern, as it's mainly for the utility
classes.

Source/Core/VideoBackends/D3D12/D3DStreamBuffer.cpp

@@ -39,7 +39,7 @@ D3DStreamBuffer::~D3DStreamBuffer()
 
 // Obviously this is non-performant, so the buffer max_size should be large enough to
 // ensure this never happens.
-bool D3DStreamBuffer::AllocateSpaceInBuffer(size_t allocation_size, size_t alignment)
+bool D3DStreamBuffer::AllocateSpaceInBuffer(size_t allocation_size, size_t alignment, bool allow_execute)
 {
 	CHECK(allocation_size <= m_buffer_max_size, "Error: Requested allocation size in D3DStreamBuffer is greater than max allowed size of backing buffer.");
 
@@ -75,7 +75,7 @@ bool D3DStreamBuffer::AllocateSpaceInBuffer(size_t allocation_size, size_t align
 
 	// Slow path. No room at front, or back, due to the GPU still (possibly) accessing parts of the buffer.
 	// Resize if possible, else stall.
-	bool command_list_executed = AttemptBufferResizeOrElseStall(allocation_size);
+	bool command_list_executed = AttemptBufferResizeOrElseStall(allocation_size, allow_execute);
 
 	return command_list_executed;
 }
@@ -113,14 +113,25 @@ void D3DStreamBuffer::AllocateBuffer(size_t size)
 	CheckHR(m_buffer->Map(0, nullptr, &m_buffer_cpu_address));
 
 	m_buffer_gpu_address = m_buffer->GetGPUVirtualAddress();
-
 	m_buffer_size = size;
+
+	// Start at the beginning of the new buffer.
+	m_buffer_gpu_completion_offset = 0;
+	m_buffer_current_allocation_offset = 0;
+	m_buffer_offset = 0;
+
+	// Notify observers.
+	if (m_buffer_reallocation_notification != nullptr)
+		*m_buffer_reallocation_notification = true;
+
+	// If we had any fences queued, they are no longer relevant.
+	ClearFences();
 }
 
 // Function returns true if current command list executed as a result of current command list
 // referencing all of buffer's contents, AND we are already at max_size. No alternative but to
 // flush. See comments above AllocateSpaceInBuffer for more details.
-bool D3DStreamBuffer::AttemptBufferResizeOrElseStall(size_t allocation_size)
+bool D3DStreamBuffer::AttemptBufferResizeOrElseStall(size_t allocation_size, bool allow_execute)
 {
 	// This function will attempt to increase the size of the buffer, in response
 	// to running out of room. If the buffer is already at its maximum size specified
@@ -155,14 +166,7 @@ bool D3DStreamBuffer::AttemptBufferResizeOrElseStall(size_t allocation_size)
 	if (new_size > m_buffer_size)
 	{
 		AllocateBuffer(new_size);
-		m_buffer_current_allocation_offset = 0;
 		m_buffer_offset = allocation_size;
-
-		if (m_buffer_reallocation_notification != nullptr)
-		{
-			*m_buffer_reallocation_notification = true;
-		}
-
 		return false;
 	}
 
@@ -177,6 +181,14 @@ bool D3DStreamBuffer::AttemptBufferResizeOrElseStall(size_t allocation_size)
 		return false;
 	}
 
+	// If allow_execute is false, the caller cannot handle command list execution (and the associated reset), so re-allocate the same-sized buffer.
+	if (!allow_execute)
+	{
+		AllocateBuffer(new_size);
+		m_buffer_offset = allocation_size;
+		return false;
+	}
+
 	// 4) If we get to this point, that means there is no outstanding queued GPU work, and we're still out of room.
 	// This is bad - and performance will suffer due to the CPU/GPU serialization, but the show must go on.
 
@@ -188,6 +200,7 @@ bool D3DStreamBuffer::AttemptBufferResizeOrElseStall(size_t allocation_size)
 	m_buffer_offset = allocation_size;
 	m_buffer_current_allocation_offset = 0;
 	m_buffer_gpu_completion_offset = 0;
+	ClearFences();
 
 	return true;
 }
@@ -299,7 +312,7 @@ void D3DStreamBuffer::UpdateGPUProgress()
 		}
 		else
 		{
-			// Fences are stored in assending order, so once we hit a fence we haven't yet crossed on GPU, abort search.
+			// Fences are stored in ascending order, so once we hit a fence we haven't yet crossed on GPU, abort search.
 			break;
 		}
 	}
@@ -312,6 +325,12 @@ void D3DStreamBuffer::QueueFenceCallback(void* owning_object, UINT64 fence_value
 		owning_stream_buffer->QueueFence(fence_value);
 }
 
+void D3DStreamBuffer::ClearFences()
+{
+	while (!m_queued_fences.empty())
+		m_queued_fences.pop();
+}
+
 bool D3DStreamBuffer::HasBufferOffsetChangedSinceLastFence() const
 {
 	if (m_queued_fences.empty())

Source/Core/VideoBackends/D3D12/D3DStreamBuffer.h

@@ -17,7 +17,7 @@ public:
 	D3DStreamBuffer(size_t initial_size, size_t max_size, bool* buffer_reallocation_notification);
 	~D3DStreamBuffer();
 
-	bool AllocateSpaceInBuffer(size_t allocation_size, size_t alignment);
+	bool AllocateSpaceInBuffer(size_t allocation_size, size_t alignment, bool allow_execute = true);
 	void OverrideSizeOfPreviousAllocation(size_t override_allocation_size);
 
 	void*                     GetBaseCPUAddress() const;
@@ -32,7 +32,7 @@ public:
 
 private:
 	void AllocateBuffer(size_t size);
-	bool AttemptBufferResizeOrElseStall(size_t new_size);
+	bool AttemptBufferResizeOrElseStall(size_t allocation_size, bool allow_execute);
 
 	bool AttemptToAllocateOutOfExistingUnusedSpaceInBuffer(size_t allocation_size);
 
@@ -40,6 +40,7 @@ private:
 
 	void UpdateGPUProgress();
 
+	void ClearFences();
 	bool HasBufferOffsetChangedSinceLastFence() const;
 	void QueueFence(UINT64 fence_value);