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/**
* Copyright (c) 2018 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
* notice, this list of conditions and the following disclaimer;
* 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
* A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
* OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
* SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
* LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
* DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
* THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
* OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*
* Authors: Daniel Carvalho
*/
/**
* @file
* Declaration of a Re-Reference Interval Prediction replacement policy.
*
* Not-Recently Used (NRU) is an approximation of LRU that uses a single bit
* to determine if an entry is going to be re-referenced in the near or distant
* future.
*
* Re-Reference Interval Prediction (RRIP) is an extension of NRU that uses a
* re-reference prediction value to determine if entries are going to be re-
* used in the near future or not.
*
* The higher the value of the RRPV, the more distant the entry is from its
* next access.
*
* Bimodal Re-Reference Interval Prediction (BRRIP) is an extension of RRIP
* that has a probability of not inserting entries as the LRU. This probability
* is controlled by the bimodal throtle parameter (btp).
*
* From the original paper, this implementation of RRIP is also called
* Static RRIP (SRRIP), as it always inserts entries with the same RRPV.
*/
#ifndef __MEM_CACHE_REPLACEMENT_POLICIES_BRRIP_RP_HH__
#define __MEM_CACHE_REPLACEMENT_POLICIES_BRRIP_RP_HH__
#include "mem/cache/replacement_policies/base.hh"
struct BRRIPRPParams;
class BRRIPRP : public BaseReplacementPolicy
{
protected:
/** BRRIP-specific implementation of replacement data. */
struct BRRIPReplData : ReplacementData
{
/**
* Re-Reference Interval Prediction Value.
* A value equal to max_RRPV + 1 indicates an invalid entry.
*/
int rrpv;
/**
* Default constructor. Invalidate data.
*/
BRRIPReplData(const int max_RRPV) : rrpv(max_RRPV + 1) {}
};
/**
* Maximum Re-Reference Prediction Value possible. An entry with this
* value as the rrpv has the longest possible re-reference interval,
* that is, it is likely not to be used in the near future, and is
* among the best eviction candidates.
* A maxRRPV of 1 implies in a NRU.
*/
const int maxRRPV;
/**
* The hit priority (HP) policy replaces entries that do not receive cache
* hits over any cache entry that receives a hit, while the frequency
* priority (FP) policy replaces infrequently re-referenced entries.
*/
const bool hitPriority;
/**
* Bimodal throtle parameter. Value in the range [0,100] used to decide
* if a new entry is inserted with long or distant re-reference.
*/
const unsigned btp;
public:
/** Convenience typedef. */
typedef BRRIPRPParams Params;
/**
* Construct and initiliaze this replacement policy.
*/
BRRIPRP(const Params *p);
/**
* Destructor.
*/
~BRRIPRP() {}
/**
* Invalidate replacement data to set it as the next probable victim.
* Set RRPV as the the most distant re-reference.
*
* @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.
*
* @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.
* Set RRPV according to the insertion policy used.
*
* @param replacement_data Replacement data to be reset.
*/
void reset(const std::shared_ptr<ReplacementData>& replacement_data) const
override;
/**
* Find replacement victim using rrpv.
*
* @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;
};
#endif // __MEM_CACHE_REPLACEMENT_POLICIES_BRRIP_RP_HH__
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