src/mem/cache/tags/sector_tags.cc

   1 /*
   2  * Copyright (c) 2018, 2020 Inria
   3  * All rights reserved.
   4  *
   5  * Redistribution and use in source and binary forms, with or without
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  10  * notice, this list of conditions and the following disclaimer in the
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  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
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  26  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  27  */
  28
  29 /**
  30  * @file
  31  * Definitions of a sector tag store.
  32  */
  33
  34 #include "mem/cache/tags/sector_tags.hh"
  35
  36 #include <cassert>
  37 #include <memory>
  38 #include <string>
  39
  40 #include "base/intmath.hh"
  41 #include "base/logging.hh"
  42 #include "base/types.hh"
  43 #include "mem/cache/base.hh"
  44 #include "mem/cache/replacement_policies/base.hh"
  45 #include "mem/cache/replacement_policies/replaceable_entry.hh"
  46 #include "mem/cache/tags/indexing_policies/base.hh"
  47
  48 SectorTags::SectorTags(const SectorTagsParams *p)
  49     : BaseTags(p), allocAssoc(p->assoc),
  50       sequentialAccess(p->sequential_access),
  51       replacementPolicy(p->replacement_policy),
  52       numBlocksPerSector(p->num_blocks_per_sector),
  53       numSectors(numBlocks / numBlocksPerSector),
  54       sectorShift(floorLog2(blkSize)), sectorMask(numBlocksPerSector - 1),
  55       sectorStats(stats, *this)
  56 {
  57     // Check parameters
  58     fatal_if(blkSize < 4 || !isPowerOf2(blkSize),
  59              "Block size must be at least 4 and a power of 2");
  60     fatal_if(!isPowerOf2(numBlocksPerSector),
  61              "# of blocks per sector must be non-zero and a power of 2");
  62 }
  63
  64 void
  65 SectorTags::tagsInit()
  66 {
  67     // Create blocks and sector blocks
  68     blks = std::vector<SectorSubBlk>(numBlocks);
  69     secBlks = std::vector<SectorBlk>(numSectors);
  70
  71     // Initialize all blocks
  72     unsigned blk_index = 0;       // index into blks array
  73     for (unsigned sec_blk_index = 0; sec_blk_index < numSectors;
  74          sec_blk_index++)
  75     {
  76         // Locate next cache sector
  77         SectorBlk* sec_blk = &secBlks[sec_blk_index];
  78
  79         // Associate a replacement data entry to the sector
  80         sec_blk->replacementData = replacementPolicy->instantiateEntry();
  81
  82         // Initialize all blocks in this sector
  83         sec_blk->blks.resize(numBlocksPerSector);
  84         for (unsigned k = 0; k < numBlocksPerSector; ++k){
  85             // Select block within the set to be linked
  86             SectorSubBlk*& blk = sec_blk->blks[k];
  87
  88             // Locate next cache block
  89             blk = &blks[blk_index];
  90
  91             // Associate a data chunk to the block
  92             blk->data = &dataBlks[blkSize*blk_index];
  93
  94             // Associate sector block to this block
  95             blk->setSectorBlock(sec_blk);
  96
  97             // Associate the sector replacement data to this block
  98             blk->replacementData = sec_blk->replacementData;
  99
 100             // Set its index and sector offset
 101             blk->setSectorOffset(k);
 102
 103             // Update block index
 104             ++blk_index;
 105         }
 106
 107         // Link block to indexing policy
 108         indexingPolicy->setEntry(sec_blk, sec_blk_index);
 109     }
 110 }
 111
 112 void
 113 SectorTags::invalidate(CacheBlk *blk)
 114 {
 115     BaseTags::invalidate(blk);
 116
 117     // Get block's sector
 118     SectorSubBlk* sub_blk = static_cast<SectorSubBlk*>(blk);
 119     const SectorBlk* sector_blk = sub_blk->getSectorBlock();
 120
 121     // When a block in a sector is invalidated, it does not make the tag
 122     // invalid automatically, as there might be other blocks in the sector
 123     // using it. The tag is invalidated only when there is a single block
 124     // in the sector.
 125     if (!sector_blk->isValid()) {
 126         // Decrease the number of tags in use
 127         stats.tagsInUse--;
 128
 129         // Invalidate replacement data, as we're invalidating the sector
 130         replacementPolicy->invalidate(sector_blk->replacementData);
 131     }
 132 }
 133
 134 CacheBlk*
 135 SectorTags::accessBlock(Addr addr, bool is_secure, Cycles &lat)
 136 {
 137     CacheBlk *blk = findBlock(addr, is_secure);
 138
 139     // Access all tags in parallel, hence one in each way.  The data side
 140     // either accesses all blocks in parallel, or one block sequentially on
 141     // a hit.  Sequential access with a miss doesn't access data.
 142     stats.tagAccesses += allocAssoc;
 143     if (sequentialAccess) {
 144         if (blk != nullptr) {
 145             stats.dataAccesses += 1;
 146         }
 147     } else {
 148         stats.dataAccesses += allocAssoc*numBlocksPerSector;
 149     }
 150
 151     // If a cache hit
 152     if (blk != nullptr) {
 153         // Update number of references to accessed block
 154         blk->increaseRefCount();
 155
 156         // Get block's sector
 157         SectorSubBlk* sub_blk = static_cast<SectorSubBlk*>(blk);
 158         const SectorBlk* sector_blk = sub_blk->getSectorBlock();
 159
 160         // Update replacement data of accessed block, which is shared with
 161         // the whole sector it belongs to
 162         replacementPolicy->touch(sector_blk->replacementData);
 163     }
 164
 165     // The tag lookup latency is the same for a hit or a miss
 166     lat = lookupLatency;
 167
 168     return blk;
 169 }
 170
 171 void
 172 SectorTags::insertBlock(const PacketPtr pkt, CacheBlk *blk)
 173 {
 174     // Get block's sector
 175     SectorSubBlk* sub_blk = static_cast<SectorSubBlk*>(blk);
 176     const SectorBlk* sector_blk = sub_blk->getSectorBlock();
 177
 178     // When a block is inserted, the tag is only a newly used tag if the
 179     // sector was not previously present in the cache.
 180     if (sector_blk->isValid()) {
 181         // An existing entry's replacement data is just updated
 182         replacementPolicy->touch(sector_blk->replacementData);
 183     } else {
 184         // Increment tag counter
 185         stats.tagsInUse++;
 186
 187         // A new entry resets the replacement data
 188         replacementPolicy->reset(sector_blk->replacementData);
 189     }
 190
 191     // Do common block insertion functionality
 192     BaseTags::insertBlock(pkt, blk);
 193 }
 194
 195 CacheBlk*
 196 SectorTags::findBlock(Addr addr, bool is_secure) const
 197 {
 198     // Extract sector tag
 199     const Addr tag = extractTag(addr);
 200
 201     // The address can only be mapped to a specific location of a sector
 202     // due to sectors being composed of contiguous-address entries
 203     const Addr offset = extractSectorOffset(addr);
 204
 205     // Find all possible sector entries that may contain the given address
 206     const std::vector<ReplaceableEntry*> entries =
 207         indexingPolicy->getPossibleEntries(addr);
 208
 209     // Search for block
 210     for (const auto& sector : entries) {
 211         auto blk = static_cast<SectorBlk*>(sector)->blks[offset];
 212         if (blk->matchTag(tag, is_secure)) {
 213             return blk;
 214         }
 215     }
 216
 217     // Did not find block
 218     return nullptr;
 219 }
 220
 221 CacheBlk*
 222 SectorTags::findVictim(Addr addr, const bool is_secure, const std::size_t size,
 223                        std::vector<CacheBlk*>& evict_blks)
 224 {
 225     // Get possible entries to be victimized
 226     const std::vector<ReplaceableEntry*> sector_entries =
 227         indexingPolicy->getPossibleEntries(addr);
 228
 229     // Check if the sector this address belongs to has been allocated
 230     Addr tag = extractTag(addr);
 231     SectorBlk* victim_sector = nullptr;
 232     for (const auto& sector : sector_entries) {
 233         SectorBlk* sector_blk = static_cast<SectorBlk*>(sector);
 234         if (sector_blk->matchTag(tag, is_secure)) {
 235             victim_sector = sector_blk;
 236             break;
 237         }
 238     }
 239
 240     // If the sector is not present
 241     if (victim_sector == nullptr){
 242         // Choose replacement victim from replacement candidates
 243         victim_sector = static_cast<SectorBlk*>(replacementPolicy->getVictim(
 244                                                 sector_entries));
 245     }
 246
 247     // Get the entry of the victim block within the sector
 248     SectorSubBlk* victim = victim_sector->blks[extractSectorOffset(addr)];
 249
 250     // Get evicted blocks. Blocks are only evicted if the sectors mismatch and
 251     // the currently existing sector is valid.
 252     if (victim_sector->matchTag(tag, is_secure)) {
 253         // It would be a hit if victim was valid, and upgrades do not call
 254         // findVictim, so it cannot happen
 255         assert(!victim->isValid());
 256     } else {
 257         // The whole sector must be evicted to make room for the new sector
 258         for (const auto& blk : victim_sector->blks){
 259             if (blk->isValid()) {
 260                 evict_blks.push_back(blk);
 261             }
 262         }
 263     }
 264
 265     // Update number of sub-blocks evicted due to a replacement
 266     sectorStats.evictionsReplacement[evict_blks.size()]++;
 267
 268     return victim;
 269 }
 270
 271 int
 272 SectorTags::extractSectorOffset(Addr addr) const
 273 {
 274     return (addr >> sectorShift) & sectorMask;
 275 }
 276
 277 Addr
 278 SectorTags::regenerateBlkAddr(const CacheBlk* blk) const
 279 {
 280     const SectorSubBlk* blk_cast = static_cast<const SectorSubBlk*>(blk);
 281     const SectorBlk* sec_blk = blk_cast->getSectorBlock();
 282     const Addr sec_addr =
 283         indexingPolicy->regenerateAddr(blk->getTag(), sec_blk);
 284     return sec_addr | ((Addr)blk_cast->getSectorOffset() << sectorShift);
 285 }
 286
 287 SectorTags::SectorTagsStats::SectorTagsStats(BaseTagStats &base_group,
 288     SectorTags& _tags)
 289   : Stats::Group(&base_group), tags(_tags),
 290     evictionsReplacement(this, "evictions_replacement",
 291         "Number of blocks evicted due to a replacement")
 292 {
 293 }
 294
 295 void
 296 SectorTags::SectorTagsStats::regStats()
 297 {
 298     Stats::Group::regStats();
 299
 300     evictionsReplacement.init(tags.numBlocksPerSector + 1);
 301     for (unsigned i = 0; i <= tags.numBlocksPerSector; ++i) {
 302         evictionsReplacement.subname(i, std::to_string(i));
 303         evictionsReplacement.subdesc(i, "Number of replacements that caused " \
 304             "the eviction of " + std::to_string(i) + " blocks");
 305     }
 306 }
 307
 308 void
 309 SectorTags::forEachBlk(std::function<void(CacheBlk &)> visitor)
 310 {
 311     for (SectorSubBlk& blk : blks) {
 312         visitor(blk);
 313     }
 314 }
 315
 316 bool
 317 SectorTags::anyBlk(std::function<bool(CacheBlk &)> visitor)
 318 {
 319     for (SectorSubBlk& blk : blks) {
 320         if (visitor(blk)) {
 321             return true;
 322         }
 323     }
 324     return false;
 325 }
 326
 327 SectorTags *
 328 SectorTagsParams::create()
 329 {
 330     // There must be a indexing policy
 331     fatal_if(!indexing_policy, "An indexing policy is required");
 332
 333     return new SectorTags(this);
 334 }