src/mem/cache/replacement_policies/lfu_rp.hh

/**
 * Copyright (c) 2018-2020 Inria
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are
 * met: redistributions of source code must retain the above copyright
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 * redistributions in binary form must reproduce the above copyright
 * notice, this list of conditions and the following disclaimer in the
 * documentation and/or other materials provided with the distribution;
 * neither the name of the copyright holders nor the names of its
 * contributors may be used to endorse or promote products derived from
 * this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
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/**
 * @file
 * Declaration of a Least Frequently Used replacement policy.
 * The victim is chosen using the reference frequency. The least referenced
 * entry is always chosen to be evicted, regardless of the amount of times
 * it has been touched, or how long has passed since its last touch.
 */

#ifndef __MEM_CACHE_REPLACEMENT_POLICIES_LFU_RP_HH__
#define __MEM_CACHE_REPLACEMENT_POLICIES_LFU_RP_HH__

#include "mem/cache/replacement_policies/base.hh"

struct LFURPParams;

namespace ReplacementPolicy {

class LFU : public Base
{
  protected:
    /** LFU-specific implementation of replacement data. */
    struct LFUReplData : ReplacementData
    {
        /** Number of references to this entry since it was reset. */
        unsigned refCount;

        /**
         * Default constructor. Invalidate data.
         */
        LFUReplData() : refCount(0) {}
    };

  public:
    typedef LFURPParams Params;
    LFU(const Params &p);
    ~LFU() = default;

    /**
     * Invalidate replacement data to set it as the next probable victim.
     * Clear the number of references.
     *
     * @param replacement_data Replacement data to be invalidated.
     */
    void invalidate(const std::shared_ptr<ReplacementData>& replacement_data)
                                                              const override;

    /**
     * Touch an entry to update its replacement data.
     * Increase number of references.
     *
     * @param replacement_data Replacement data to be touched.
     */
    void touch(const std::shared_ptr<ReplacementData>& replacement_data) const
                                                                     override;

    /**
     * Reset replacement data. Used when an entry is inserted.
     * Reset number of references.
     *
     * @param replacement_data Replacement data to be reset.
     */
    void reset(const std::shared_ptr<ReplacementData>& replacement_data) const
                                                                     override;

    /**
     * Find replacement victim using reference frequency.
     *
     * @param cands Replacement candidates, selected by indexing policy.
     * @return Replacement entry to be replaced.
     */
    ReplaceableEntry* getVictim(const ReplacementCandidates& candidates) const
                                                                     override;

    /**
     * Instantiate a replacement data entry.
     *
     * @return A shared pointer to the new replacement data.
     */
    std::shared_ptr<ReplacementData> instantiateEntry() override;
};

} // namespace ReplacementPolicy

#endif // __MEM_CACHE_REPLACEMENT_POLICIES_LFU_RP_HH__