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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: Javier Bueno
*/
/**
* Implementation of the Access Map Pattern Matching Prefetcher
*
* References:
* Access map pattern matching for high performance data cache prefetch.
* Ishii, Y., Inaba, M., & Hiraki, K. (2011).
* Journal of Instruction-Level Parallelism, 13, 1-24.
*/
#ifndef __MEM_CACHE_PREFETCH_ACCESS_MAP_PATTERN_MATCHING_HH__
#define __MEM_CACHE_PREFETCH_ACCESS_MAP_PATTERN_MATCHING_HH__
#include "mem/cache/base.hh"
#include "mem/cache/prefetch/associative_set.hh"
#include "mem/cache/prefetch/queued.hh"
#include "mem/packet.hh"
struct AccessMapPatternMatchingPrefetcherParams;
class AccessMapPatternMatchingPrefetcher : public QueuedPrefetcher
{
/** Maximum number of prefetch generated */
const unsigned startDegree;
/** Amount of memory covered by a hot zone */
const uint64_t hotZoneSize;
/** A prefetch coverage factor bigger than this is considered high */
const double highCoverageThreshold;
/** A prefetch coverage factor smaller than this is considered low */
const double lowCoverageThreshold;
/** A prefetch accuracy factor bigger than this is considered high */
const double highAccuracyThreshold;
/** A prefetch accuracy factor smaller than this is considered low */
const double lowAccuracyThreshold;
/** A cache hit ratio bigger than this is considered high */
const double highCacheHitThreshold;
/** A cache hit ratio smaller than this is considered low */
const double lowCacheHitThreshold;
/** Cycles in an epoch period */
const Cycles epochCycles;
/** Off chip memory latency to use for the epoch bandwidth calculation */
const Tick offChipMemoryLatency;
/** Data type representing the state of a cacheline in the access map */
enum AccessMapState
{
AM_INIT,
AM_PREFETCH,
AM_ACCESS,
AM_INVALID
};
/** AccessMapEntry data type */
struct AccessMapEntry : public TaggedEntry
{
/** vector containing the state of the cachelines in this zone */
std::vector<AccessMapState> states;
AccessMapEntry(size_t num_entries) : states(num_entries, AM_INIT)
{}
/** Reset the entries to their initial values */
void reset() override
{
for (auto &entry : states) {
entry = AM_INIT;
}
}
};
/** Access map table */
AssociativeSet<AccessMapEntry> accessMapTable;
/**
* Number of good prefetches
* - State transitions from PREFETCH to ACCESS
*/
uint64_t numGoodPrefetches;
/**
* Number of prefetches issued
* - State transitions from INIT to PREFETCH
*/
uint64_t numTotalPrefetches;
/**
* Number of raw cache misses
* - State transitions from INIT or PREFETCH to ACCESS
*/
uint64_t numRawCacheMisses;
/**
* Number of raw cache hits
* - State transitions from ACCESS to ACCESS
*/
uint64_t numRawCacheHits;
/** Current degree */
unsigned degree;
/** Current useful degree */
unsigned usefulDegree;
/**
* Given a target cacheline, this function checks if the cachelines
* that follow the provided stride have been accessed. If so, the line
* is considered a good candidate.
* @param states vector containing the states of three contiguous hot zones
* @param current target block (cacheline)
* @param stride access stride to obtain the reference cachelines
* @return true if current is a prefetch candidate
*/
inline bool checkCandidate(std::vector<AccessMapState> const &states,
Addr current, int stride) const
{
enum AccessMapState tgt = states[current - stride];
enum AccessMapState s = states[current + stride];
enum AccessMapState s2 = states[current + 2 * stride];
enum AccessMapState s2_p1 = states[current + 2 * stride + 1];
return (tgt != AM_INVALID &&
((s == AM_ACCESS && s2 == AM_ACCESS) ||
(s == AM_ACCESS && s2_p1 == AM_ACCESS)));
}
/**
* Obtain an AccessMapEntry from the AccessMapTable, if the entry is not
* found a new one is initialized and inserted.
* @param am_addr address of the hot zone
* @param is_secure whether the address belongs to the secure memory area
* @return the corresponding entry
*/
AccessMapEntry *getAccessMapEntry(Addr am_addr, bool is_secure);
/**
* Updates the state of a block within an AccessMapEntry, also updates
* the prefetcher metrics.
* @param entry AccessMapEntry to update
* @param block cacheline within the hot zone
* @param state new state
*/
void setEntryState(AccessMapEntry &entry, Addr block,
enum AccessMapState state);
/**
* This event constitues the epoch of the statistics that keep track of
* the prefetcher accuracy, when this event triggers, the prefetcher degree
* is adjusted and the statistics counters are reset.
*/
void processEpochEvent();
EventFunctionWrapper epochEvent;
public:
AccessMapPatternMatchingPrefetcher(
const AccessMapPatternMatchingPrefetcherParams* p);
~AccessMapPatternMatchingPrefetcher() {}
void calculatePrefetch(const PrefetchInfo &pfi,
std::vector<AddrPriority> &addresses) override;
};
#endif//__MEM_CACHE_PREFETCH_ACCESS_MAP_PATTERN_MATCHING_HH__
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