src/mem/cache/tags/sector_tags.cc

   1 /*
   2  * Copyright (c) 2018 Inria
   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: Daniel Carvalho
  29  */
  30
  31 /**
  32  * @file
  33  * Definitions of a sector tag store.
  34  */
  35
  36 #include "mem/cache/tags/sector_tags.hh"
  37
  38 #include <cassert>
  39 #include <memory>
  40 #include <string>
  41
  42 #include "base/intmath.hh"
  43 #include "base/logging.hh"
  44 #include "base/types.hh"
  45 #include "mem/cache/base.hh"
  46 #include "mem/cache/replacement_policies/base.hh"
  47 #include "mem/cache/replacement_policies/replaceable_entry.hh"
  48 #include "mem/cache/tags/indexing_policies/base.hh"
  49
  50 SectorTags::SectorTags(const SectorTagsParams *p)
  51     : BaseTags(p), allocAssoc(p->assoc),
  52       sequentialAccess(p->sequential_access),
  53       replacementPolicy(p->replacement_policy),
  54       numBlocksPerSector(p->num_blocks_per_sector),
  55       numSectors(numBlocks / numBlocksPerSector),
  56       sectorShift(floorLog2(blkSize)), sectorMask(numBlocksPerSector - 1)
  57 {
  58     // Check parameters
  59     fatal_if(blkSize < 4 || !isPowerOf2(blkSize),
  60              "Block size must be at least 4 and a power of 2");
  61     fatal_if(!isPowerOf2(numBlocksPerSector),
  62              "# of blocks per sector must be non-zero and a power of 2");
  63 }
  64
  65 void
  66 SectorTags::tagsInit()
  67 {
  68     // Create blocks and sector blocks
  69     blks = std::vector<SectorSubBlk>(numBlocks);
  70     secBlks = std::vector<SectorBlk>(numSectors);
  71
  72     // Initialize all blocks
  73     unsigned blk_index = 0;       // index into blks array
  74     for (unsigned sec_blk_index = 0; sec_blk_index < numSectors;
  75          sec_blk_index++)
  76     {
  77         // Locate next cache sector
  78         SectorBlk* sec_blk = &secBlks[sec_blk_index];
  79
  80         // Link block to indexing policy
  81         indexingPolicy->setEntry(sec_blk, sec_blk_index);
  82
  83         // Associate a replacement data entry to the sector
  84         sec_blk->replacementData = replacementPolicy->instantiateEntry();
  85
  86         // Initialize all blocks in this sector
  87         sec_blk->blks.resize(numBlocksPerSector);
  88         for (unsigned k = 0; k < numBlocksPerSector; ++k){
  89             // Select block within the set to be linked
  90             SectorSubBlk*& blk = sec_blk->blks[k];
  91
  92             // Locate next cache block
  93             blk = &blks[blk_index];
  94
  95             // Associate a data chunk to the block
  96             blk->data = &dataBlks[blkSize*blk_index];
  97
  98             // Associate sector block to this block
  99             blk->setSectorBlock(sec_blk);
 100
 101             // Associate the sector replacement data to this block
 102             blk->replacementData = sec_blk->replacementData;
 103
 104             // Set its index and sector offset
 105             blk->setSectorOffset(k);
 106
 107             // Update block index
 108             ++blk_index;
 109         }
 110     }
 111 }
 112
 113 void
 114 SectorTags::invalidate(CacheBlk *blk)
 115 {
 116     BaseTags::invalidate(blk);
 117
 118     // Get block's sector
 119     SectorSubBlk* sub_blk = static_cast<SectorSubBlk*>(blk);
 120     const SectorBlk* sector_blk = sub_blk->getSectorBlock();
 121
 122     // When a block in a sector is invalidated, it does not make the tag
 123     // invalid automatically, as there might be other blocks in the sector
 124     // using it. The tag is invalidated only when there is a single block
 125     // in the sector.
 126     if (!sector_blk->isValid()) {
 127         // Decrease the number of tags in use
 128         tagsInUse--;
 129
 130         // Invalidate replacement data, as we're invalidating the sector
 131         replacementPolicy->invalidate(sector_blk->replacementData);
 132     }
 133 }
 134
 135 CacheBlk*
 136 SectorTags::accessBlock(Addr addr, bool is_secure, Cycles &lat)
 137 {
 138     CacheBlk *blk = findBlock(addr, is_secure);
 139
 140     // Access all tags in parallel, hence one in each way.  The data side
 141     // either accesses all blocks in parallel, or one block sequentially on
 142     // a hit.  Sequential access with a miss doesn't access data.
 143     tagAccesses += allocAssoc;
 144     if (sequentialAccess) {
 145         if (blk != nullptr) {
 146             dataAccesses += 1;
 147         }
 148     } else {
 149         dataAccesses += allocAssoc*numBlocksPerSector;
 150     }
 151
 152     // If a cache hit
 153     if (blk != nullptr) {
 154         // Update number of references to accessed block
 155         blk->refCount++;
 156
 157         // Get block's sector
 158         SectorSubBlk* sub_blk = static_cast<SectorSubBlk*>(blk);
 159         const SectorBlk* sector_blk = sub_blk->getSectorBlock();
 160
 161         // Update replacement data of accessed block, which is shared with
 162         // the whole sector it belongs to
 163         replacementPolicy->touch(sector_blk->replacementData);
 164     }
 165
 166     // The tag lookup latency is the same for a hit or a miss
 167     lat = lookupLatency;
 168
 169     return blk;
 170 }
 171
 172 void
 173 SectorTags::insertBlock(const PacketPtr pkt, CacheBlk *blk)
 174 {
 175     // Get block's sector
 176     SectorSubBlk* sub_blk = static_cast<SectorSubBlk*>(blk);
 177     const SectorBlk* sector_blk = sub_blk->getSectorBlock();
 178
 179     // When a block is inserted, the tag is only a newly used tag if the
 180     // sector was not previously present in the cache.
 181     if (sector_blk->isValid()) {
 182         // An existing entry's replacement data is just updated
 183         replacementPolicy->touch(sector_blk->replacementData);
 184     } else {
 185         // Increment tag counter
 186         tagsInUse++;
 187
 188         // A new entry resets the replacement data
 189         replacementPolicy->reset(sector_blk->replacementData);
 190     }
 191
 192     // Do common block insertion functionality
 193     BaseTags::insertBlock(pkt, blk);
 194 }
 195
 196 CacheBlk*
 197 SectorTags::findBlock(Addr addr, bool is_secure) const
 198 {
 199     // Extract sector tag
 200     const Addr tag = extractTag(addr);
 201
 202     // The address can only be mapped to a specific location of a sector
 203     // due to sectors being composed of contiguous-address entries
 204     const Addr offset = extractSectorOffset(addr);
 205
 206     // Find all possible sector entries that may contain the given address
 207     const std::vector<ReplaceableEntry*> entries =
 208         indexingPolicy->getPossibleEntries(addr);
 209
 210     // Search for block
 211     for (const auto& sector : entries) {
 212         auto blk = static_cast<SectorBlk*>(sector)->blks[offset];
 213         if (blk->getTag() == tag && blk->isValid() &&
 214             blk->isSecure() == is_secure) {
 215             return blk;
 216         }
 217     }
 218
 219     // Did not find block
 220     return nullptr;
 221 }
 222
 223 CacheBlk*
 224 SectorTags::findVictim(Addr addr, const bool is_secure, const std::size_t size,
 225                        std::vector<CacheBlk*>& evict_blks) const
 226 {
 227     // Get possible entries to be victimized
 228     const std::vector<ReplaceableEntry*> sector_entries =
 229         indexingPolicy->getPossibleEntries(addr);
 230
 231     // Check if the sector this address belongs to has been allocated
 232     Addr tag = extractTag(addr);
 233     SectorBlk* victim_sector = nullptr;
 234     for (const auto& sector : sector_entries) {
 235         SectorBlk* sector_blk = static_cast<SectorBlk*>(sector);
 236         if ((tag == sector_blk->getTag()) && sector_blk->isValid() &&
 237             (is_secure == sector_blk->isSecure())){
 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 ((tag == victim_sector->getTag()) &&
 256         (is_secure == victim_sector->isSecure())){
 257         // It would be a hit if victim was valid, and upgrades do not call
 258         // findVictim, so it cannot happen
 259         assert(!victim->isValid());
 260     } else {
 261         // The whole sector must be evicted to make room for the new sector
 262         for (const auto& blk : victim_sector->blks){
 263             evict_blks.push_back(blk);
 264         }
 265     }
 266
 267     return victim;
 268 }
 269
 270 int
 271 SectorTags::extractSectorOffset(Addr addr) const
 272 {
 273     return (addr >> sectorShift) & sectorMask;
 274 }
 275
 276 Addr
 277 SectorTags::regenerateBlkAddr(const CacheBlk* blk) const
 278 {
 279     const SectorSubBlk* blk_cast = static_cast<const SectorSubBlk*>(blk);
 280     const SectorBlk* sec_blk = blk_cast->getSectorBlock();
 281     const Addr sec_addr = indexingPolicy->regenerateAddr(blk->tag, sec_blk);
 282     return sec_addr | ((Addr)blk_cast->getSectorOffset() << sectorShift);
 283 }
 284
 285 void
 286 SectorTags::forEachBlk(std::function<void(CacheBlk &)> visitor)
 287 {
 288     for (SectorSubBlk& blk : blks) {
 289         visitor(blk);
 290     }
 291 }
 292
 293 bool
 294 SectorTags::anyBlk(std::function<bool(CacheBlk &)> visitor)
 295 {
 296     for (SectorSubBlk& blk : blks) {
 297         if (visitor(blk)) {
 298             return true;
 299         }
 300     }
 301     return false;
 302 }
 303
 304 SectorTags *
 305 SectorTagsParams::create()
 306 {
 307     // There must be a indexing policy
 308     fatal_if(!indexing_policy, "An indexing policy is required");
 309
 310     return new SectorTags(this);
 311 }