chromium/third_party/ruy/src/ruy/prepacked_cache.h

/* Copyright 2019 Google LLC. All Rights Reserved.

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

    http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
==============================================================================*/

#ifndef RUY_RUY_PREPACKED_CACHE_H_
#define RUY_RUY_PREPACKED_CACHE_H_

#include <cstddef>
#include <cstdint>
#include <unordered_map>

#include "ruy/mat.h"

namespace ruy {

// "Low effort" Least Recently Used Cache for Prepacked Matrices
// A cache mechanism for prepacked matrices that ejects oldest entries.
// The implementation is "low effort" in the following ways:
//  - we just linearly search for the oldest entry when doing an ejection
//  - the ejection policy is very simple: if the new size would be above the
// .  threshold, we will eject entries until the size is below the threshold.
// Current use cases (RNNs with GEMV operations) indicate that ejection is rare
// and memory constraints are tight, so we devote no additional storage to the
// LRU mechanism and accept O(n) search to eject oldest entry. In practice,
// the number of total entries has not been shown to be large.
//
// An instance of PrepackedCache is always owned by a Context. Just like
// Context, no "thread safety" consideration is applicable to this class:
// no two threads may simulaneously be accessing the same instance.
class PrepackedCache final { … };

}  // namespace ruy

#endif  // RUY_RUY_PREPACKED_CACHE_H_