src/mem/cache/tags/lru.cc

   1 /*
   2  * Copyright (c) 2003-2005 The Regents of The University of Michigan
   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: Erik Hallnor
  29  */
  30
  31 /**
  32  * @file
  33  * Definitions of LRU tag store.
  34  */
  35
  36 #include <string>
  37
  38 #include "mem/cache/base.hh"
  39 #include "base/intmath.hh"
  40 #include "mem/cache/tags/lru.hh"
  41 #include "sim/core.hh"
  42 #include "cacheset.hh"
  43
  44 using namespace std;
  45
  46 // create and initialize a LRU/MRU cache structure
  47 LRU::LRU(unsigned _numSets, unsigned _blkSize, unsigned _assoc,
  48          unsigned _hit_latency)
  49     : numSets(_numSets), blkSize(_blkSize), assoc(_assoc),
  50       hitLatency(_hit_latency)
  51 {
  52     // Check parameters
  53     if (blkSize < 4 || !isPowerOf2(blkSize)) {
  54         fatal("Block size must be at least 4 and a power of 2");
  55     }
  56     if (numSets <= 0 || !isPowerOf2(numSets)) {
  57         fatal("# of sets must be non-zero and a power of 2");
  58     }
  59     if (assoc <= 0) {
  60         fatal("associativity must be greater than zero");
  61     }
  62     if (hitLatency <= 0) {
  63         fatal("access latency must be greater than zero");
  64     }
  65
  66     blkMask = blkSize - 1;
  67     setShift = floorLog2(blkSize);
  68     setMask = numSets - 1;
  69     tagShift = setShift + floorLog2(numSets);
  70     warmedUp = false;
  71     /** @todo Make warmup percentage a parameter. */
  72     warmupBound = numSets * assoc;
  73
  74     sets = new CacheSet[numSets];
  75     blks = new BlkType[numSets * assoc];
  76     // allocate data storage in one big chunk
  77     dataBlks = new uint8_t[numSets*assoc*blkSize];
  78
  79     unsigned blkIndex = 0;       // index into blks array
  80     for (unsigned i = 0; i < numSets; ++i) {
  81         sets[i].assoc = assoc;
  82
  83         sets[i].blks = new BlkType*[assoc];
  84
  85         // link in the data blocks
  86         for (unsigned j = 0; j < assoc; ++j) {
  87             // locate next cache block
  88             BlkType *blk = &blks[blkIndex];
  89             blk->data = &dataBlks[blkSize*blkIndex];
  90             ++blkIndex;
  91
  92             // invalidate new cache block
  93             blk->status = 0;
  94
  95             //EGH Fix Me : do we need to initialize blk?
  96
  97             // Setting the tag to j is just to prevent long chains in the hash
  98             // table; won't matter because the block is invalid
  99             blk->tag = j;
 100             blk->whenReady = 0;
 101             blk->isTouched = false;
 102             blk->size = blkSize;
 103             sets[i].blks[j]=blk;
 104             blk->set = i;
 105         }
 106     }
 107 }
 108
 109 LRU::~LRU()
 110 {
 111     delete [] dataBlks;
 112     delete [] blks;
 113     delete [] sets;
 114 }
 115
 116 LRU::BlkType*
 117 LRU::accessBlock(Addr addr, int &lat, int context_src)
 118 {
 119     Addr tag = extractTag(addr);
 120     unsigned set = extractSet(addr);
 121     BlkType *blk = sets[set].findBlk(tag);
 122     lat = hitLatency;
 123     if (blk != NULL) {
 124         // move this block to head of the MRU list
 125         sets[set].moveToHead(blk);
 126         DPRINTF(CacheRepl, "set %x: moving blk %x to MRU\n",
 127                 set, regenerateBlkAddr(tag, set));
 128         if (blk->whenReady > curTick
 129             && blk->whenReady - curTick > hitLatency) {
 130             lat = blk->whenReady - curTick;
 131         }
 132         blk->refCount += 1;
 133     }
 134
 135     return blk;
 136 }
 137
 138
 139 LRU::BlkType*
 140 LRU::findBlock(Addr addr) const
 141 {
 142     Addr tag = extractTag(addr);
 143     unsigned set = extractSet(addr);
 144     BlkType *blk = sets[set].findBlk(tag);
 145     return blk;
 146 }
 147
 148 LRU::BlkType*
 149 LRU::findVictim(Addr addr, PacketList &writebacks)
 150 {
 151     unsigned set = extractSet(addr);
 152     // grab a replacement candidate
 153     BlkType *blk = sets[set].blks[assoc-1];
 154     if (blk->isValid()) {
 155         replacements[0]++;
 156         totalRefs += blk->refCount;
 157         ++sampledRefs;
 158         blk->refCount = 0;
 159
 160         DPRINTF(CacheRepl, "set %x: selecting blk %x for replacement\n",
 161                 set, regenerateBlkAddr(blk->tag, set));
 162     }
 163     return blk;
 164 }
 165
 166 void
 167 LRU::insertBlock(Addr addr, BlkType *blk, int context_src)
 168 {
 169     if (!blk->isTouched) {
 170         tagsInUse++;
 171         blk->isTouched = true;
 172         if (!warmedUp && tagsInUse.value() >= warmupBound) {
 173             warmedUp = true;
 174             warmupCycle = curTick;
 175         }
 176     }
 177
 178     // Set tag for new block.  Caller is responsible for setting status.
 179     blk->tag = extractTag(addr);
 180
 181     unsigned set = extractSet(addr);
 182     sets[set].moveToHead(blk);
 183 }
 184
 185 void
 186 LRU::invalidateBlk(BlkType *blk)
 187 {
 188     if (blk) {
 189         blk->status = 0;
 190         blk->isTouched = false;
 191         blk->clearLoadLocks();
 192         tagsInUse--;
 193     }
 194 }
 195
 196 void
 197 LRU::cleanupRefs()
 198 {
 199     for (unsigned i = 0; i < numSets*assoc; ++i) {
 200         if (blks[i].isValid()) {
 201             totalRefs += blks[i].refCount;
 202             ++sampledRefs;
 203         }
 204     }
 205 }