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/**
* Copyright (c) 2018 Metempsy Technology Consulting
* 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: Ivan Pizarro
*/
/**
* Implementation of the 'A Best-Offset Prefetcher'
* Reference:
* Michaud, P. (2015, June). A best-offset prefetcher.
* In 2nd Data Prefetching Championship.
*/
#ifndef __MEM_CACHE_PREFETCH_BOP_HH__
#define __MEM_CACHE_PREFETCH_BOP_HH__
#include <queue>
#include "mem/cache/prefetch/queued.hh"
#include "mem/packet.hh"
struct BOPPrefetcherParams;
class BOPPrefetcher : public QueuedPrefetcher
{
private:
enum RRWay {
Left,
Right
};
/** Learning phase parameters */
const unsigned int scoreMax;
const unsigned int roundMax;
const unsigned int badScore;
/** Recent requests table parameteres */
const unsigned int rrEntries;
const unsigned int tagMask;
/** Delay queue parameters */
const bool delayQueueEnabled;
const unsigned int delayQueueSize;
const unsigned int delayTicks;
std::vector<Addr> rrLeft;
std::vector<Addr> rrRight;
/** Structure to save the offset and the score */
typedef std::pair<int16_t, uint8_t> OffsetListEntry;
std::vector<OffsetListEntry> offsetsList;
/** In a first implementation of the BO prefetcher, both banks of the
* RR were written simultaneously when a prefetched line is inserted
* into the cache. Adding the delay queue tries to avoid always
* striving for timeless prefetches, which has been found to not
* always being optimal.
*/
struct DelayQueueEntry
{
Addr baseAddr;
Tick processTick;
DelayQueueEntry(Addr x, Tick t) : baseAddr(x), processTick(t)
{}
};
std::deque<DelayQueueEntry> delayQueue;
/** Event to handle the delay queue processing */
void delayQueueEventWrapper();
EventFunctionWrapper delayQueueEvent;
/** Hardware prefetcher enabled */
bool issuePrefetchRequests;
/** Current best offset to issue prefetches */
Addr bestOffset;
/** Current best offset found in the learning phase */
Addr phaseBestOffset;
/** Current test offset index */
std::vector<OffsetListEntry>::iterator offsetsListIterator;
/** Max score found so far */
unsigned int bestScore;
/** Current round */
unsigned int round;
/** Generate a hash for the specified address to index the RR table
* @param addr: address to hash
* @param way: RR table to which is addressed (left/right)
*/
unsigned int hash(Addr addr, unsigned int way) const;
/** Insert the specified address into the RR table
* @param addr: address to insert
* @param way: RR table to which the address will be inserted
*/
void insertIntoRR(Addr addr, unsigned int way);
/** Insert the specified address into the delay queue. This will
* trigger an event after the delay cycles pass
* @param addr: address to insert into the delay queue
*/
void insertIntoDelayQueue(Addr addr);
/** Reset all the scores from the offset list */
void resetScores();
/** Generate the tag for the specified address based on the tag bits
* and the block size
* @param addr: address to get the tag from
*/
Addr tag(Addr addr) const;
/** Test if @X-O is hitting in the RR table to update the
offset score */
bool testRR(Addr) const;
/** Learning phase of the BOP. Update the intermediate values of the
round and update the best offset if found */
void bestOffsetLearning(Addr);
/** Update the RR right table after a prefetch fill */
void notifyFill(const PacketPtr& pkt) override;
public:
BOPPrefetcher(const BOPPrefetcherParams *p);
~BOPPrefetcher() {}
void calculatePrefetch(const PrefetchInfo &pfi,
std::vector<AddrPriority> &addresses) override;
};
#endif /* __MEM_CACHE_PREFETCH_BOP_HH__ */
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