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28 * Authors: Javier Bueno
32 * Implementation of the Indirect Memory Prefetcher
35 * IMP: Indirect memory prefetcher.
36 * Yu, X., Hughes, C. J., Satish, N., & Devadas, S. (2015, December).
37 * In Proceedings of the 48th International Symposium on Microarchitecture
41 #ifndef __MEM_CACHE_PREFETCH_INDIRECT_MEMORY_HH__
42 #define __MEM_CACHE_PREFETCH_INDIRECT_MEMORY_HH__
46 #include "base/sat_counter.hh"
47 #include "mem/cache/prefetch/associative_set.hh"
48 #include "mem/cache/prefetch/queued.hh"
50 struct IndirectMemoryPrefetcherParams;
52 class IndirectMemoryPrefetcher : public QueuedPrefetcher
54 /** Maximum number of prefetches generated per event */
55 const unsigned int maxPrefetchDistance;
56 /** Shift values considered */
57 const std::vector<int> shiftValues;
58 /** Counter threshold to start prefetching */
59 const unsigned int prefetchThreshold;
60 /** streamCounter value to trigger the streaming prefetcher */
61 const int streamCounterThreshold;
62 /** Number of prefetches generated when using the streaming prefetcher */
63 const int streamingDistance;
65 /** Prefetch Table Entry */
66 struct PrefetchTableEntry : public TaggedEntry
68 /* Stream table fields */
70 /** Accessed address */
72 /** Whether this address is in the secure region */
74 /** Confidence counter of the stream */
75 unsigned int streamCounter;
77 /* Indirect table fields */
79 /** Enable bit of the indirect fields */
81 /** Current index value */
83 /** BaseAddr detected */
87 /** Confidence counter of the indirect fields */
88 SatCounter indirectCounter;
90 * This variable is set to indicate that there has been at least one
91 * match with the current index value. This information is later used
92 * when a new index is updated. If there were no increases in the
93 * indirectCounter, the counter is decremented.
95 bool increasedIndirectCounter;
97 PrefetchTableEntry(unsigned indirect_counter_bits)
98 : TaggedEntry(), address(0), secure(false), streamCounter(0),
99 enabled(false), index(0), baseAddr(0), shift(0),
100 indirectCounter(indirect_counter_bits),
101 increasedIndirectCounter(false)
104 void reset() override {
112 indirectCounter.reset();
113 increasedIndirectCounter = false;
116 /** Prefetch table */
117 AssociativeSet<PrefetchTableEntry> prefetchTable;
119 /** Indirect Pattern Detector entrt */
120 struct IndirectPatternDetectorEntry : public TaggedEntry
126 /** Valid bit for the second index */
128 /** Number of misses currently recorded */
131 * Potential BaseAddr candidates for each recorded miss.
132 * The number of candidates per miss is determined by the number of
133 * elements in the shiftValues array.
135 std::vector<std::vector<Addr>> baseAddr;
137 IndirectPatternDetectorEntry(unsigned int num_addresses,
138 unsigned int num_shifts)
139 : idx1(0), idx2(0), secondIndexSet(false), numMisses(0),
140 baseAddr(num_addresses, std::vector<Addr>(num_shifts))
143 void reset() override {
146 secondIndexSet = false;
151 /** Indirect Pattern Detector (IPD) table */
152 AssociativeSet<IndirectPatternDetectorEntry> ipd;
154 /** Entry currently tracking misses */
155 IndirectPatternDetectorEntry *ipdEntryTrackingMisses;
157 /** Byte order used to access the cache */
158 const ByteOrder byteOrder;
161 * Allocate or update an entry in the IPD
162 * @param pt_entry Pointer to the associated page table entry
163 * @param index Detected first index value
165 void allocateOrUpdateIPDEntry(const PrefetchTableEntry *pt_entry,
168 * Update an IPD entry with a detected miss address, when the first index
170 * @param miss_addr The address that caused the miss
172 void trackMissIndex1(Addr miss_addr);
175 * Update an IPD entry with a detected miss address, when the second index
177 * @param miss_addr The address that caused the miss
179 void trackMissIndex2(Addr miss_addr);
182 * Checks if an access to the cache matches any active PT entry, if so,
183 * the indirect confidence counter is incremented
184 * @param addr address of the access
186 void checkAccessMatchOnActiveEntries(Addr addr);
189 IndirectMemoryPrefetcher(const IndirectMemoryPrefetcherParams *p);
190 ~IndirectMemoryPrefetcher() {}
192 void calculatePrefetch(const PrefetchInfo &pfi,
193 std::vector<AddrPriority> &addresses) override;
195 #endif//__MEM_CACHE_PREFETCH_INDIRECT_MEMORY_HH__