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/* -*- 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
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