src/mem/cache/tags/sector_tags.cc

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