Use first-fit policy to reduce upload memory.

Reverts CL9160 by replacing the existing policy with one
that re-uses smaller ring-buffers.

Before
*RESULT BufferUploadPerfRun/D3D12_SetSubData: wall_time= 397865.698113 ns
*RESULT BufferUploadPerfRun/D3D12_SetSubData: wall_time= 398025.660377 ns
*RESULT BufferUploadPerfRun/D3D12_SetSubData: wall_time= 438816.754717 ns

After
*RESULT BufferUploadPerfRun/D3D12_SetSubData: wall_time= 118189.847059 ns
*RESULT BufferUploadPerfRun/D3D12_SetSubData: wall_time= 116808.235294 ns
*RESULT BufferUploadPerfRun/D3D12_SetSubData: wall_time= 117133.964706 ns

No change for Vulkan. About 3x faster with D3D.

BUG=dawn:211

Change-Id: Iaa6b0ef50305bf7df482f7e10e92353320039965
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/10441
Commit-Queue: Bryan Bernhart <bryan.bernhart@intel.com>
Reviewed-by: Corentin Wallez <cwallez@chromium.org>

src/dawn_native/Buffer.cpp

@@ -255,12 +255,8 @@ namespace dawn_native {
         DynamicUploader* uploader = nullptr;
         DAWN_TRY_ASSIGN(uploader, GetDevice()->GetDynamicUploader());
 
-        // TODO(bryan.bernhart@intel.com): Remove once alignment constraint is added to validation
-        // (dawn:73). D3D12 does not specify so we assume 4-byte alignment to be safe.
-        static constexpr size_t kDefaultAlignment = 4;
-
         UploadHandle uploadHandle;
-        DAWN_TRY_ASSIGN(uploadHandle, uploader->Allocate(count, kDefaultAlignment));
+        DAWN_TRY_ASSIGN(uploadHandle, uploader->Allocate(count));
         ASSERT(uploadHandle.mappedBuffer != nullptr);
 
         memcpy(uploadHandle.mappedBuffer, data, count);

src/dawn_native/DynamicUploader.cpp

@@ -41,31 +41,41 @@ namespace dawn_native {
         return {};
     }
 
-    ResultOrError<UploadHandle> DynamicUploader::Allocate(uint32_t size, uint32_t alignment) {
+    ResultOrError<UploadHandle> DynamicUploader::Allocate(uint32_t size) {
-        ASSERT(IsPowerOfTwo(alignment));
+        // Note: Validation ensures size is already aligned.
+        // First-fit: find next smallest buffer large enough to satisfy the allocation request.
+        RingBuffer* targetRingBuffer = GetLargestBuffer();
+        for (auto& ringBuffer : mRingBuffers) {
+            // Prevent overflow.
+            ASSERT(ringBuffer->GetSize() >= ringBuffer->GetUsedSize());
+            const size_t remainingSize = ringBuffer->GetSize() - ringBuffer->GetUsedSize();
+            if (size <= remainingSize) {
+                targetRingBuffer = ringBuffer.get();
+                break;
+            }
+        }
 
-        // Align the requested allocation size
+        UploadHandle uploadHandle = UploadHandle{};
-        const size_t alignedSize = Align(size, alignment);
+        if (targetRingBuffer != nullptr) {
-
+            uploadHandle = targetRingBuffer->SubAllocate(size);
-        RingBuffer* largestRingBuffer = GetLargestBuffer();
+        }
-        UploadHandle uploadHandle = largestRingBuffer->SubAllocate(alignedSize);
 
         // Upon failure, append a newly created (and much larger) ring buffer to fulfill the
         // request.
         if (uploadHandle.mappedBuffer == nullptr) {
             // Compute the new max size (in powers of two to preserve alignment).
-            size_t newMaxSize = largestRingBuffer->GetSize();
+            size_t newMaxSize = targetRingBuffer->GetSize() * 2;
             while (newMaxSize < size) {
                 newMaxSize *= 2;
             }
 
             // TODO(bryan.bernhart@intel.com): Fall-back to no sub-allocations should this fail.
             DAWN_TRY(CreateAndAppendBuffer(newMaxSize));
-            largestRingBuffer = GetLargestBuffer();
+            targetRingBuffer = GetLargestBuffer();
-            uploadHandle = largestRingBuffer->SubAllocate(alignedSize);
+            uploadHandle = targetRingBuffer->SubAllocate(size);
         }
 
-        uploadHandle.stagingBuffer = largestRingBuffer->GetStagingBuffer();
+        uploadHandle.stagingBuffer = targetRingBuffer->GetStagingBuffer();
 
         return uploadHandle;
     }

src/dawn_native/DynamicUploader.h

@@ -29,12 +29,12 @@ namespace dawn_native {
 
         // We add functions to Create/Release StagingBuffers to the DynamicUploader as there's
         // currently no place to track the allocated staging buffers such that they're freed after
-        // pending coommands are finished. This should be changed when better resource allocation is
+        // pending commands are finished. This should be changed when better resource allocation is
         // implemented.
         ResultOrError<std::unique_ptr<StagingBufferBase>> CreateStagingBuffer(size_t size);
         void ReleaseStagingBuffer(std::unique_ptr<StagingBufferBase> stagingBuffer);
 
-        ResultOrError<UploadHandle> Allocate(uint32_t requiredSize, uint32_t alignment);
+        ResultOrError<UploadHandle> Allocate(uint32_t size);
         void Tick(Serial lastCompletedSerial);
 
         RingBuffer* GetLargestBuffer();