1 files changed, 96 insertions, 0 deletions
diff --git a/gfx/layers/mlgpu/BufferCache.cpp b/gfx/layers/mlgpu/BufferCache.cpp
new file mode 100644
index 0000000000..8a2668a5ef
--- /dev/null
+++ b/gfx/layers/mlgpu/BufferCache.cpp
@@ -0,0 +1,96 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "BufferCache.h"
+#include "MLGDevice.h"
+#include "ShaderDefinitionsMLGPU.h"
+#include "mozilla/MathAlgorithms.h"
+
+namespace mozilla {
+namespace layers {
+
+using namespace mlg;
+
+BufferCache::BufferCache(MLGDevice* aDevice)
+    : mDevice(aDevice),
+      mFirstSizeClass(CeilingLog2(kConstantBufferElementSize)),
+      mFrameNumber(0),
+      mNextSizeClassToShrink(0) {
+  // Create a cache of buffers for each size class, where each size class is a
+  // power of 2 between the minimum and maximum size of a constant buffer.
+  size_t maxBindSize = mDevice->GetMaxConstantBufferBindSize();
+  MOZ_ASSERT(IsPowerOfTwo(maxBindSize));
+
+  size_t lastSizeClass = CeilingLog2(maxBindSize);
+  MOZ_ASSERT(lastSizeClass >= mFirstSizeClass);
+
+  mCaches.resize(lastSizeClass - mFirstSizeClass + 1);
+}
+
+BufferCache::~BufferCache() = default;
+
+RefPtr<MLGBuffer> BufferCache::GetOrCreateBuffer(size_t aBytes) {
+  size_t sizeClass = CeilingLog2(aBytes);
+  size_t sizeClassIndex = sizeClass - mFirstSizeClass;
+  if (sizeClassIndex >= mCaches.size()) {
+    return mDevice->CreateBuffer(MLGBufferType::Constant, aBytes,
+                                 MLGUsage::Dynamic, nullptr);
+  }
+
+  CachePool& pool = mCaches[sizeClassIndex];
+
+  // See if we've cached a buffer that wasn't used in the past 2 frames. A
+  // buffer used this frame could have already been mapped and written to, and a
+  // buffer used the previous frame might still be in-use by the GPU. While the
+  // latter case is okay, it causes aliasing in the driver. Since content is
+  // double buffered we do not let the compositor get more than 1 frames ahead,
+  // and a count of 2 frames should ensure the buffer is unused.
+  if (!pool.empty() && mFrameNumber >= pool.front().mLastUsedFrame + 2) {
+    RefPtr<MLGBuffer> buffer = pool.front().mBuffer;
+    pool.pop_front();
+    pool.push_back(CacheEntry(mFrameNumber, buffer));
+    MOZ_RELEASE_ASSERT(buffer->GetSize() >= aBytes);
+    return buffer;
+  }
+
+  // Allocate a new buffer and cache it.
+  size_t bytes = (size_t(1) << sizeClass);
+  MOZ_ASSERT(bytes >= aBytes);
+
+  RefPtr<MLGBuffer> buffer = mDevice->CreateBuffer(
+      MLGBufferType::Constant, bytes, MLGUsage::Dynamic, nullptr);
+  if (!buffer) {
+    return nullptr;
+  }
+
+  pool.push_back(CacheEntry(mFrameNumber, buffer));
+  return buffer;
+}
+
+void BufferCache::EndFrame() {
+  // Consider a buffer dead after ~5 seconds assuming 60 fps.
+  static size_t kMaxUnusedFrameCount = 60 * 5;
+
+  // At the end of each frame we pick one size class and see if it has any
+  // buffers that haven't been used for many frames. If so we clear them.
+  // The next frame we'll search the next size class. (This is just to spread
+  // work over more than one frame.)
+  CachePool& pool = mCaches[mNextSizeClassToShrink];
+  while (!pool.empty()) {
+    // Since the deque is sorted oldest-to-newest, front-to-back, we can stop
+    // searching as soon as a buffer is active.
+    if (mFrameNumber - pool.front().mLastUsedFrame < kMaxUnusedFrameCount) {
+      break;
+    }
+    pool.pop_front();
+  }
+  mNextSizeClassToShrink = (mNextSizeClassToShrink + 1) % mCaches.size();
+
+  mFrameNumber++;
+}
+
+}  // namespace layers
+}  // namespace mozilla