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_cache.hh"
  39 #include "base/intmath.hh"
  40 #include "mem/cache/tags/lru.hh"
  41 #include "sim/root.hh"
  42
  43 using namespace std;
  44
  45 LRUBlk*
  46 CacheSet::findBlk(int asid, Addr tag) const
  47 {
  48     for (int i = 0; i < assoc; ++i) {
  49         if (blks[i]->tag == tag && blks[i]->isValid()) {
  50             return blks[i];
  51         }
  52     }
  53     return 0;
  54 }
  55
  56
  57 void
  58 CacheSet::moveToHead(LRUBlk *blk)
  59 {
  60     // nothing to do if blk is already head
  61     if (blks[0] == blk)
  62         return;
  63
  64     // write 'next' block into blks[i], moving up from MRU toward LRU
  65     // until we overwrite the block we moved to head.
  66
  67     // start by setting up to write 'blk' into blks[0]
  68     int i = 0;
  69     LRUBlk *next = blk;
  70
  71     do {
  72         assert(i < assoc);
  73         // swap blks[i] and next
  74         LRUBlk *tmp = blks[i];
  75         blks[i] = next;
  76         next = tmp;
  77         ++i;
  78     } while (next != blk);
  79 }
  80
  81
  82 // create and initialize a LRU/MRU cache structure
  83 LRU::LRU(int _numSets, int _blkSize, int _assoc, int _hit_latency) :
  84     numSets(_numSets), blkSize(_blkSize), assoc(_assoc), hitLatency(_hit_latency)
  85 {
  86     // Check parameters
  87     if (blkSize < 4 || !isPowerOf2(blkSize)) {
  88         fatal("Block size must be at least 4 and a power of 2");
  89     }
  90     if (numSets <= 0 || !isPowerOf2(numSets)) {
  91         fatal("# of sets must be non-zero and a power of 2");
  92     }
  93     if (assoc <= 0) {
  94         fatal("associativity must be greater than zero");
  95     }
  96     if (hitLatency <= 0) {
  97         fatal("access latency must be greater than zero");
  98     }
  99
 100     LRUBlk  *blk;
 101     int i, j, blkIndex;
 102
 103     blkMask = blkSize - 1;
 104     setShift = floorLog2(blkSize);
 105     setMask = numSets - 1;
 106     tagShift = setShift + floorLog2(numSets);
 107     warmedUp = false;
 108     /** @todo Make warmup percentage a parameter. */
 109     warmupBound = numSets * assoc;
 110
 111     sets = new CacheSet[numSets];
 112     blks = new LRUBlk[numSets * assoc];
 113     // allocate data storage in one big chunk
 114     dataBlks = new uint8_t[numSets*assoc*blkSize];
 115
 116     blkIndex = 0;       // index into blks array
 117     for (i = 0; i < numSets; ++i) {
 118         sets[i].assoc = assoc;
 119
 120         sets[i].blks = new LRUBlk*[assoc];
 121
 122         // link in the data blocks
 123         for (j = 0; j < assoc; ++j) {
 124             // locate next cache block
 125             blk = &blks[blkIndex];
 126             blk->data = &dataBlks[blkSize*blkIndex];
 127             ++blkIndex;
 128
 129             // invalidate new cache block
 130             blk->status = 0;
 131
 132             //EGH Fix Me : do we need to initialize blk?
 133
 134             // Setting the tag to j is just to prevent long chains in the hash
 135             // table; won't matter because the block is invalid
 136             blk->tag = j;
 137             blk->whenReady = 0;
 138             blk->asid = -1;
 139             blk->isTouched = false;
 140             blk->size = blkSize;
 141             sets[i].blks[j]=blk;
 142             blk->set = i;
 143         }
 144     }
 145 }
 146
 147 LRU::~LRU()
 148 {
 149     delete [] dataBlks;
 150     delete [] blks;
 151     delete [] sets;
 152 }
 153
 154 // probe cache for presence of given block.
 155 bool
 156 LRU::probe(int asid, Addr addr) const
 157 {
 158     //  return(findBlock(Read, addr, asid) != 0);
 159     Addr tag = extractTag(addr);
 160     unsigned myset = extractSet(addr);
 161
 162     LRUBlk *blk = sets[myset].findBlk(asid, tag);
 163
 164     return (blk != NULL);       // true if in cache
 165 }
 166
 167 LRUBlk*
 168 LRU::findBlock(Addr addr, int asid, int &lat)
 169 {
 170     Addr tag = extractTag(addr);
 171     unsigned set = extractSet(addr);
 172     LRUBlk *blk = sets[set].findBlk(asid, tag);
 173     lat = hitLatency;
 174     if (blk != NULL) {
 175         // move this block to head of the MRU list
 176         sets[set].moveToHead(blk);
 177         if (blk->whenReady > curTick
 178             && blk->whenReady - curTick > hitLatency) {
 179             lat = blk->whenReady - curTick;
 180         }
 181         blk->refCount += 1;
 182     }
 183
 184     return blk;
 185 }
 186
 187 LRUBlk*
 188 LRU::findBlock(Packet * &pkt, int &lat)
 189 {
 190     Addr addr = pkt->getAddr();
 191     int asid = pkt->req->getAsid();
 192
 193     Addr tag = extractTag(addr);
 194     unsigned set = extractSet(addr);
 195     LRUBlk *blk = sets[set].findBlk(asid, tag);
 196     lat = hitLatency;
 197     if (blk != NULL) {
 198         // move this block to head of the MRU list
 199         sets[set].moveToHead(blk);
 200         if (blk->whenReady > curTick
 201             && blk->whenReady - curTick > hitLatency) {
 202             lat = blk->whenReady - curTick;
 203         }
 204         blk->refCount += 1;
 205     }
 206
 207     return blk;
 208 }
 209
 210 LRUBlk*
 211 LRU::findBlock(Addr addr, int asid) const
 212 {
 213     Addr tag = extractTag(addr);
 214     unsigned set = extractSet(addr);
 215     LRUBlk *blk = sets[set].findBlk(asid, tag);
 216     return blk;
 217 }
 218
 219 LRUBlk*
 220 LRU::findReplacement(Packet * &pkt, PacketList &writebacks,
 221                      BlkList &compress_blocks)
 222 {
 223     unsigned set = extractSet(pkt->getAddr());
 224     // grab a replacement candidate
 225     LRUBlk *blk = sets[set].blks[assoc-1];
 226     sets[set].moveToHead(blk);
 227     if (blk->isValid()) {
 228         replacements[0]++;
 229         totalRefs += blk->refCount;
 230         ++sampledRefs;
 231         blk->refCount = 0;
 232     } else if (!blk->isTouched) {
 233         tagsInUse++;
 234         blk->isTouched = true;
 235         if (!warmedUp && tagsInUse.value() >= warmupBound) {
 236             warmedUp = true;
 237             warmupCycle = curTick;
 238         }
 239     }
 240
 241     return blk;
 242 }
 243
 244 void
 245 LRU::invalidateBlk(int asid, Addr addr)
 246 {
 247     LRUBlk *blk = findBlock(addr, asid);
 248     if (blk) {
 249         blk->status = 0;
 250         blk->isTouched = false;
 251         tagsInUse--;
 252     }
 253 }
 254
 255 void
 256 LRU::doCopy(Addr source, Addr dest, int asid, PacketList &writebacks)
 257 {
 258     assert(source == blkAlign(source));
 259     assert(dest == blkAlign(dest));
 260     LRUBlk *source_blk = findBlock(source, asid);
 261     assert(source_blk);
 262     LRUBlk *dest_blk = findBlock(dest, asid);
 263     if (dest_blk == NULL) {
 264         // Need to do a replacement
 265         Request *search = new Request(dest,1,0);
 266         Packet * pkt = new Packet(search, Packet::ReadReq, -1);
 267         BlkList dummy_list;
 268         dest_blk = findReplacement(pkt, writebacks, dummy_list);
 269         if (dest_blk->isValid() && dest_blk->isModified()) {
 270             // Need to writeback data.
 271 /*          pkt = buildWritebackReq(regenerateBlkAddr(dest_blk->tag,
 272                                                       dest_blk->set),
 273                                     dest_blk->req->asid,
 274                                     dest_blk->xc,
 275                                     blkSize,
 276                                     dest_blk->data,
 277                                     dest_blk->size);
 278 */
 279             Request *writebackReq = new Request(regenerateBlkAddr(dest_blk->tag,
 280                                                                   dest_blk->set),
 281                                                 blkSize, 0);
 282             Packet *writeback = new Packet(writebackReq, Packet::Writeback, -1);
 283             writeback->dataDynamic<uint8_t>(dest_blk->data);
 284             writebacks.push_back(writeback);
 285         }
 286         dest_blk->tag = extractTag(dest);
 287         dest_blk->asid = asid;
 288         delete search;
 289         delete pkt;
 290     }
 291     /**
 292      * @todo Can't assume the status once we have coherence on copies.
 293      */
 294
 295     // Set this block as readable, writeable, and dirty.
 296     dest_blk->status = 7;
 297     memcpy(dest_blk->data, source_blk->data, blkSize);
 298 }
 299
 300 void
 301 LRU::cleanupRefs()
 302 {
 303     for (int i = 0; i < numSets*assoc; ++i) {
 304         if (blks[i].isValid()) {
 305             totalRefs += blks[i].refCount;
 306             ++sampledRefs;
 307         }
 308     }
 309 }