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Reduce thread scheduling overhead in parallelFor

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This commit is contained in:
Eugene Zhulenev 2018-10-16 14:53:06 -07:00
parent d52763bb4f
commit 217d839816
1 changed files with 17 additions and 10 deletions
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27
unsupported/Eigen/CXX11/src/Tensor/TensorDeviceThreadPool.h
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@ -214,18 +214,25 @@ struct ThreadPoolDevice {
Barrier barrier(static_cast<unsigned int>(block_count));
std::function<void(Index, Index)> handleRange;
handleRange = [=, &handleRange, &barrier, &f](Index firstIdx, Index lastIdx) {
if (lastIdx - firstIdx <= block_size) {
// Single block or less, execute directly.
f(firstIdx, lastIdx);
barrier.Notify();
return;
while (lastIdx - firstIdx > block_size) {
// Split into halves and schedule the second half on a different thread.
const Index midIdx = firstIdx + divup((lastIdx - firstIdx) / 2, block_size) * block_size;
pool_->Schedule([=, &handleRange]() { handleRange(midIdx, lastIdx); });
lastIdx = midIdx;
}
// Split into halves and submit to the pool.
Index mid = firstIdx + divup((lastIdx - firstIdx) / 2, block_size) * block_size;
pool_->Schedule([=, &handleRange]() { handleRange(mid, lastIdx); });
handleRange(firstIdx, mid);
// Single block or less, execute directly.
f(firstIdx, lastIdx);
barrier.Notify();
};
handleRange(0, n);
if (block_count <= numThreads()) {
// Avoid a thread hop by running the root of the tree and one block on the
// main thread.
handleRange(0, n);
} else {
// Execute the root in the thread pool to avoid running work on more than
// numThreads() threads.
pool_->Schedule([=, &handleRange]() { handleRange(0, n); });
}
barrier.Wait();
}