indirect_memory.cc revision 13772
1/** 2 * Copyright (c) 2018 Metempsy Technology Consulting 3 * All rights reserved. 4 * 5 * Redistribution and use in source and binary forms, with or without 6 * modification, are permitted provided that the following conditions are 7 * met: redistributions of source code must retain the above copyright 8 * notice, this list of conditions and the following disclaimer; 9 * redistributions in binary form must reproduce the above copyright 10 * notice, this list of conditions and the following disclaimer in the 11 * documentation and/or other materials provided with the distribution; 12 * neither the name of the copyright holders nor the names of its 13 * contributors may be used to endorse or promote products derived from 14 * this software without specific prior written permission. 15 * 16 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS 17 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT 18 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR 19 * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT 20 * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, 21 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT 22 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, 23 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY 24 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT 25 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE 26 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 27 * 28 * Authors: Javier Bueno 29 */ 30 31 #include "mem/cache/prefetch/indirect_memory.hh" 32 33 #include "mem/cache/base.hh" 34 #include "mem/cache/prefetch/associative_set_impl.hh" 35 #include "params/IndirectMemoryPrefetcher.hh" 36 37IndirectMemoryPrefetcher::IndirectMemoryPrefetcher( 38 const IndirectMemoryPrefetcherParams *p) : QueuedPrefetcher(p), 39 maxPrefetchDistance(p->max_prefetch_distance), 40 shiftValues(p->shift_values), prefetchThreshold(p->prefetch_threshold), 41 maxIndirectCounterValue(p->max_indirect_counter_value), 42 streamCounterThreshold(p->stream_counter_threshold), 43 streamingDistance(p->streaming_distance), 44 prefetchTable(p->pt_table_assoc, p->pt_table_entries, 45 p->pt_table_indexing_policy, p->pt_table_replacement_policy), 46 ipd(p->ipd_table_assoc, p->ipd_table_entries, p->ipd_table_indexing_policy, 47 p->ipd_table_replacement_policy, 48 IndirectPatternDetectorEntry(p->addr_array_len, shiftValues.size())), 49 ipdEntryTrackingMisses(nullptr), 50#if THE_ISA != NULL_ISA 51 byteOrder(TheISA::GuestByteOrder) 52#else 53 byteOrder((ByteOrder) -1) 54#endif 55{ 56 fatal_if(byteOrder == -1, "This prefetcher requires a defined ISA\n"); 57} 58 59void 60IndirectMemoryPrefetcher::calculatePrefetch(const PrefetchInfo &pfi, 61 std::vector<AddrPriority> &addresses) 62{ 63 // This prefetcher requires a PC 64 if (!pfi.hasPC()) { 65 return; 66 } 67 68 bool is_secure = pfi.isSecure(); 69 Addr pc = pfi.getPC(); 70 Addr addr = pfi.getAddr(); 71 bool miss = pfi.isCacheMiss(); 72 73 checkAccessMatchOnActiveEntries(addr); 74 75 // First check if this is a miss, if the prefetcher is tracking misses 76 if (ipdEntryTrackingMisses != nullptr && miss) { 77 // Check if the entry tracking misses has already set its second index 78 if (!ipdEntryTrackingMisses->secondIndexSet) { 79 trackMissIndex1(addr); 80 } else { 81 trackMissIndex2(addr); 82 } 83 } else { 84 // if misses are not being tracked, attempt to detect stream accesses 85 PrefetchTableEntry *pt_entry = 86 prefetchTable.findEntry(pc, false /* unused */); 87 if (pt_entry != nullptr) { 88 prefetchTable.accessEntry(pt_entry); 89 90 if (pt_entry->address != addr) { 91 // Streaming access found 92 pt_entry->streamCounter += 1; 93 if (pt_entry->streamCounter >= streamCounterThreshold) { 94 int64_t delta = addr - pt_entry->address; 95 for (unsigned int i = 1; i <= streamingDistance; i += 1) { 96 addresses.push_back(AddrPriority(addr + delta * i, 0)); 97 } 98 } 99 pt_entry->address = addr; 100 pt_entry->secure = is_secure; 101 102 103 // if this is a read, read the data from the cache and assume 104 // it is an index (this is only possible if the data is already 105 // in the cache), also, only indexes up to 8 bytes are 106 // considered 107 108 if (!miss && !pfi.isWrite() && pfi.getSize() <= 8) { 109 int64_t index = 0; 110 switch(pfi.getSize()) { 111 case sizeof(uint8_t): 112 index = pfi.get<uint8_t>(byteOrder); 113 break; 114 case sizeof(uint16_t): 115 index = pfi.get<uint16_t>(byteOrder); 116 break; 117 case sizeof(uint32_t): 118 index = pfi.get<uint32_t>(byteOrder); 119 break; 120 case sizeof(uint64_t): 121 index = pfi.get<uint64_t>(byteOrder); 122 break; 123 default: 124 panic("Invalid access size\n"); 125 } 126 if (!pt_entry->enabled) { 127 // Not enabled (no pattern detected in this stream), 128 // add or update an entry in the pattern detector and 129 // start tracking misses 130 allocateOrUpdateIPDEntry(pt_entry, index); 131 } else { 132 // Enabled entry, update the index 133 pt_entry->index = index; 134 if (!pt_entry->increasedIndirectCounter) { 135 if (pt_entry->indirectCounter > 0) { 136 pt_entry->indirectCounter -= 1; 137 } 138 } else { 139 // Set this to false, to see if the new index 140 // has any match 141 pt_entry->increasedIndirectCounter = false; 142 } 143 144 // If the counter is high enough, start prefetching 145 if (pt_entry->indirectCounter > prefetchThreshold) { 146 unsigned distance = pt_entry->indirectCounter * 147 maxPrefetchDistance / maxIndirectCounterValue; 148 for (int delta = 1; delta < distance; delta += 1) { 149 Addr pf_addr = pt_entry->baseAddr + 150 (pt_entry->index << pt_entry->shift); 151 addresses.push_back(AddrPriority(pf_addr, 0)); 152 } 153 } 154 } 155 } 156 } 157 } else { 158 pt_entry = prefetchTable.findVictim(pc); 159 assert(pt_entry != nullptr); 160 prefetchTable.insertEntry(pc, false /* unused */, pt_entry); 161 pt_entry->address = addr; 162 pt_entry->secure = is_secure; 163 } 164 } 165} 166 167void 168IndirectMemoryPrefetcher::allocateOrUpdateIPDEntry( 169 const PrefetchTableEntry *pt_entry, int64_t index) 170{ 171 // The address of the pt_entry is used to index the IPD 172 Addr ipd_entry_addr = (Addr) pt_entry; 173 IndirectPatternDetectorEntry *ipd_entry = ipd.findEntry(ipd_entry_addr, 174 false/* unused */); 175 if (ipd_entry != nullptr) { 176 ipd.accessEntry(ipd_entry); 177 if (!ipd_entry->secondIndexSet) { 178 // Second time we see an index, fill idx2 179 ipd_entry->idx2 = index; 180 ipd_entry->secondIndexSet = true; 181 ipdEntryTrackingMisses = ipd_entry; 182 } else { 183 // Third access! no pattern has been found so far, 184 // release the IPD entry 185 ipd_entry->reset(); 186 ipdEntryTrackingMisses = nullptr; 187 } 188 } else { 189 ipd_entry = ipd.findVictim(ipd_entry_addr); 190 assert(ipd_entry != nullptr); 191 ipd.insertEntry(ipd_entry_addr, false /* unused */, ipd_entry); 192 ipd_entry->idx1 = index; 193 ipdEntryTrackingMisses = ipd_entry; 194 } 195} 196 197void 198IndirectMemoryPrefetcher::trackMissIndex1(Addr miss_addr) 199{ 200 IndirectPatternDetectorEntry *entry = ipdEntryTrackingMisses; 201 // If the second index is not set, we are just filling the baseAddr 202 // vector 203 assert(entry->numMisses < entry->baseAddr.size()); 204 std::vector<Addr> &ba_array = entry->baseAddr[entry->numMisses]; 205 int idx = 0; 206 for (int shift : shiftValues) { 207 ba_array[idx] = miss_addr - (entry->idx1 << shift); 208 idx += 1; 209 } 210 entry->numMisses += 1; 211 if (entry->numMisses == entry->baseAddr.size()) { 212 // stop tracking misses once we have tracked enough 213 ipdEntryTrackingMisses = nullptr; 214 } 215} 216void 217IndirectMemoryPrefetcher::trackMissIndex2(Addr miss_addr) 218{ 219 IndirectPatternDetectorEntry *entry = ipdEntryTrackingMisses; 220 // Second index is filled, compare the addresses generated during 221 // the previous misses (using idx1) against newly generated values 222 // using idx2, if a match is found, fill the additional fields 223 // of the PT entry 224 for (int midx = 0; midx < entry->numMisses; midx += 1) 225 { 226 std::vector<Addr> &ba_array = entry->baseAddr[midx]; 227 int idx = 0; 228 for (int shift : shiftValues) { 229 if (ba_array[idx] == (miss_addr - (entry->idx2 << shift))) { 230 // Match found! 231 // Fill the corresponding pt_entry 232 PrefetchTableEntry *pt_entry = 233 (PrefetchTableEntry *) entry->getTag(); 234 pt_entry->baseAddr = ba_array[idx]; 235 pt_entry->shift = shift; 236 pt_entry->enabled = true; 237 pt_entry->indirectCounter = 0; 238 // Release the current IPD Entry 239 entry->reset(); 240 // Do not track more misses 241 ipdEntryTrackingMisses = nullptr; 242 return; 243 } 244 idx += 1; 245 } 246 } 247} 248 249void 250IndirectMemoryPrefetcher::checkAccessMatchOnActiveEntries(Addr addr) 251{ 252 for (auto &pt_entry : prefetchTable) { 253 if (pt_entry.enabled) { 254 if (addr == pt_entry.baseAddr + 255 (pt_entry.index << pt_entry.shift)) { 256 if (pt_entry.indirectCounter < maxIndirectCounterValue) { 257 pt_entry.indirectCounter += 1; 258 pt_entry.increasedIndirectCounter = true; 259 } 260 } 261 } 262 } 263} 264 265IndirectMemoryPrefetcher* 266IndirectMemoryPrefetcherParams::create() 267{ 268 return new IndirectMemoryPrefetcher(this); 269} 270