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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 '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 <deque>
#include <unordered_map>
#include <vector>
#include "mem/cache/prefetch/queued.hh"
#include "mem/packet.hh"
struct SBOOEPrefetcherParams;
class SBOOEPrefetcher : public QueuedPrefetcher
{
private:
/** Prefetcher parameters */
const int latencyBufferSize;
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.
*/
std::deque<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)
{}
};
struct Sandbox {
/** FIFO queue. Max entries is 'sandboxEntries' */
std::vector<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;
/** Index of the oldest entry in the FIFO */
unsigned int index;
/** Sequential stride for this prefetcher */
const int stride;
Sandbox(unsigned int max_entries, int _stride)
: sandboxScore(0), lateScore(0), index(0), stride(_stride)
{
entries.resize(max_entries);
}
/**
* Insert the line address being accessed to the cache 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 insert(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 */
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:
SBOOEPrefetcher(const SBOOEPrefetcherParams *p);
void calculatePrefetch(const PrefetchInfo &pfi,
std::vector<AddrPriority> &addresses) override;
};
#endif // __MEM_CACHE_PREFETCH_SBOOE_HH__
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