[d3d11] Always use fast MAP_WRITE_DISCARD path on deferred contexts

... but keep the SingleUse option as-is anyway because games do not release
their command lists after submission and end up wasting massive amounts of
memory.

dxvk.conf

@@ -154,9 +154,11 @@
 # dxvk.tearFree = Auto
 
 
-# Assume single-use mode for command lists created on deferred contexts.
-# This may need to be disabled for some applications to avoid rendering
-# issues, which may come at a significant performance cost.
+# Assume that command lists created from deferred contexts are only used
+# once. This is extremely common and may improve performance while reducing
+# the amount of memory wasted if games keep their command list objects alive
+# for too long, but may also lead to rendering issues if command lists are
+# submitted multiple times.
 #
 # Supported values: True, False
 

src/d3d11/d3d11_context_def.cpp

@@ -265,44 +265,24 @@ namespace dxvk {
           ID3D11Resource*               pResource,
           D3D11_MAPPED_SUBRESOURCE*     pMappedResource) {
     D3D11Buffer* pBuffer = static_cast<D3D11Buffer*>(pResource);
-    
+
     if (unlikely(pBuffer->GetMapMode() == D3D11_COMMON_BUFFER_MAP_MODE_NONE)) {
       Logger::err("D3D11: Cannot map a device-local buffer");
       return E_INVALIDARG;
     }
-
+
+    auto bufferSlice = pBuffer->AllocSlice(&m_allocationCache);
+    pMappedResource->pData = bufferSlice->mapPtr();
     pMappedResource->RowPitch     = pBuffer->Desc()->ByteWidth;
     pMappedResource->DepthPitch   = pBuffer->Desc()->ByteWidth;
-
-    if (likely(m_csFlags.test(DxvkCsChunkFlag::SingleUse))) {
-      // For resources that cannot be written by the GPU,
-      // we may write to the buffer resource directly and
-      // just swap in the buffer slice as needed.
-      auto bufferSlice = pBuffer->AllocSlice(&m_allocationCache);
-      pMappedResource->pData = bufferSlice->mapPtr();
-
-      EmitCs([
-        cDstBuffer = pBuffer->GetBuffer(),
-        cDstSlice  = std::move(bufferSlice)
-      ] (DxvkContext* ctx) {
-        ctx->invalidateBuffer(cDstBuffer, Rc<DxvkResourceAllocation>(cDstSlice));
-      });
-    } else {
-      // For GPU-writable resources, we need a data slice
-      // to perform the update operation at execution time.
-      auto dataSlice = AllocUpdateBufferSlice(pBuffer->Desc()->ByteWidth);
-      pMappedResource->pData = dataSlice.ptr();
-
-      EmitCs([
-        cDstBuffer = pBuffer->GetBuffer(),
-        cDataSlice = dataSlice
-      ] (DxvkContext* ctx) {
-        Rc<DxvkResourceAllocation> slice = cDstBuffer->allocateSlice();
-        std::memcpy(slice->mapPtr(), cDataSlice.ptr(), cDataSlice.length());
-        ctx->invalidateBuffer(cDstBuffer, std::move(slice));
-      });
-    }
-
+
+    EmitCs([
+      cDstBuffer = pBuffer->GetBuffer(),
+      cDstSlice  = std::move(bufferSlice)
+    ] (DxvkContext* ctx) {
+      ctx->invalidateBuffer(cDstBuffer, Rc<DxvkResourceAllocation>(cDstSlice));
+    });
+
     return S_OK;
   }