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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.
*/
/**
* Implementation of the 'Sandbox Based Optimal Offset Estimation'
* Reference:
* Brown, N. T., & Sendag, R. Sandbox Based Optimal Offset Estimation.
*/
#ifndef __MEM_CACHE_PREFETCH_SBOOE_HH__
#define __MEM_CACHE_PREFETCH_SBOOE_HH__
#include <unordered_map>
#include <vector>
#include "base/circular_queue.hh"
#include "mem/cache/prefetch/queued.hh"
#include "mem/packet.hh"
struct SBOOEPrefetcherParams;
namespace Prefetcher {
class SBOOE : public Queued
{
private:
/** Prefetcher parameters */
const int sequentialPrefetchers;
/** Threshold used to issue prefetchers */
const unsigned int scoreThreshold;
/**
* Holds the current demand addresses and tick. This is later used to
* calculate the average latency buffer when the address is filled in
* the cache.
*/
std::unordered_map<Addr, Tick> demandAddresses;
/**
* The latency buffer holds the elapsed ticks between the demand and
* the fill in the cache for the latest N accesses which are used to
* calculate the average access latency which is later used to
* predict if a prefetcher would be filled on time if issued.
*/
CircularQueue<Tick> latencyBuffer;
/** Holds the current average access latency */
Tick averageAccessLatency;
/** Holds the current sum of the latency buffer latency */
Tick latencyBufferSum;
struct SandboxEntry {
/** Cache line predicted by the candidate prefetcher */
Addr line;
/** Tick when the simulated prefetch is expected to be filled */
Tick expectedArrivalTick;
/** To indicate if it was initialized */
bool valid;
SandboxEntry()
: valid(false)
{}
};
class Sandbox
{
private:
/** FIFO queue containing the sandbox entries. */
CircularQueue<SandboxEntry> entries;
/**
* Accesses during the eval period that were present
* in the sandbox
*/
unsigned int sandboxScore;
/** Hits in the sandbox that wouldn't have been filled on time */
unsigned int lateScore;
public:
/** Sequential stride for this prefetcher */
const int stride;
Sandbox(unsigned int max_entries, int _stride)
: entries(max_entries), sandboxScore(0), lateScore(0),
stride(_stride)
{
}
/**
* Update score and insert the line address being accessed into the
* FIFO queue of the sandbox.
*
* @param line Line address being accessed
* @param tick Tick in which the access is expected to be filled
*/
void access(Addr line, Tick tick);
/** Calculate the useful score
* @return Useful score of the sandbox. Sandbox score adjusted by
* by the late score
*/
unsigned int score() const { return (sandboxScore - lateScore); }
};
std::vector<Sandbox> sandboxes;
/** Current best sandbox */
const Sandbox* bestSandbox;
/** Number of accesses notified to the prefetcher */
unsigned int accesses;
/**
* Process an access to the specified line address and update the
* sandbox counters counters.
* @param line Address of the line being accessed
* @return TRUE if the evaluation finished, FALSE otherwise
*/
bool access(Addr line);
/** Update the latency buffer after a prefetch fill */
void notifyFill(const PacketPtr& pkt) override;
public:
SBOOE(const SBOOEPrefetcherParams &p);
void calculatePrefetch(const PrefetchInfo &pfi,
std::vector<AddrPriority> &addresses) override;
};
} // namespace Prefetcher
#endif // __MEM_CACHE_PREFETCH_SBOOE_HH__