src/mem/cache/tags/fa_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 a fully associative LRU tagstore.
  34  */
  35
  36 #include <sstream>
  37
  38 #include <assert.h>
  39
  40 #include "mem/cache/tags/fa_lru.hh"
  41 #include "base/intmath.hh"
  42 #include "base/misc.hh"
  43
  44 using namespace std;
  45
  46 FALRU::FALRU(int _blkSize, int _size, int hit_latency)
  47     : blkSize(_blkSize), size(_size),
  48       numBlks(size/blkSize), hitLatency(hit_latency)
  49 {
  50     if (!isPowerOf2(blkSize))
  51         fatal("cache block size (in bytes) `%d' must be a power of two",
  52               blkSize);
  53     if (!(hitLatency > 0))
  54         fatal("Access latency in cycles must be at least one cycle");
  55     if (!isPowerOf2(size))
  56         fatal("Cache Size must be power of 2 for now");
  57
  58     // Track all cache sizes from 128K up by powers of 2
  59     numCaches = floorLog2(size) - 17;
  60     if (numCaches >0){
  61         cacheBoundaries = new FALRUBlk *[numCaches];
  62         cacheMask = (1 << numCaches) - 1;
  63     } else {
  64         cacheMask = 0;
  65     }
  66
  67     warmedUp = false;
  68     warmupBound = size/blkSize;
  69
  70     blks = new FALRUBlk[numBlks];
  71     head = &(blks[0]);
  72     tail = &(blks[numBlks-1]);
  73
  74     head->prev = NULL;
  75     head->next = &(blks[1]);
  76     head->inCache = cacheMask;
  77
  78     tail->prev = &(blks[numBlks-2]);
  79     tail->next = NULL;
  80     tail->inCache = 0;
  81
  82     int index = (1 << 17) / blkSize;
  83     int j = 0;
  84     int flags = cacheMask;
  85     for (int i = 1; i < numBlks-1; i++) {
  86         blks[i].inCache = flags;
  87         if (i == index - 1){
  88             cacheBoundaries[j] = &(blks[i]);
  89             flags &= ~ (1<<j);
  90             ++j;
  91             index = index << 1;
  92         }
  93         blks[i].prev = &(blks[i-1]);
  94         blks[i].next = &(blks[i+1]);
  95         blks[i].isTouched = false;
  96     }
  97     assert(j == numCaches);
  98     assert(index == numBlks);
  99     //assert(check());
 100 }
 101
 102 void
 103 FALRU::regStats(const string &name)
 104 {
 105     using namespace Stats;
 106     BaseTags::regStats(name);
 107     hits
 108         .init(numCaches+1)
 109         .name(name + ".falru_hits")
 110         .desc("The number of hits in each cache size.")
 111         ;
 112     misses
 113         .init(numCaches+1)
 114         .name(name + ".falru_misses")
 115         .desc("The number of misses in each cache size.")
 116         ;
 117     accesses
 118         .name(name + ".falru_accesses")
 119         .desc("The number of accesses to the FA LRU cache.")
 120         ;
 121
 122     for (int i = 0; i < numCaches+1; ++i) {
 123         stringstream size_str;
 124         if (i < 3){
 125             size_str << (1<<(i+7)) <<"K";
 126         } else {
 127             size_str << (1<<(i-3)) <<"M";
 128         }
 129
 130         hits.subname(i, size_str.str());
 131         hits.subdesc(i, "Hits in a " + size_str.str() +" cache");
 132         misses.subname(i, size_str.str());
 133         misses.subdesc(i, "Misses in a " + size_str.str() +" cache");
 134     }
 135 }
 136
 137 FALRUBlk *
 138 FALRU::hashLookup(Addr addr) const
 139 {
 140     tagIterator iter = tagHash.find(addr);
 141     if (iter != tagHash.end()) {
 142         return (*iter).second;
 143     }
 144     return NULL;
 145 }
 146
 147 void
 148 FALRU::invalidateBlk(FALRU::BlkType *blk)
 149 {
 150     if (blk) {
 151         blk->status = 0;
 152         blk->isTouched = false;
 153         tagsInUse--;
 154     }
 155 }
 156
 157 FALRUBlk*
 158 FALRU::accessBlock(Addr addr, int &lat, int *inCache)
 159 {
 160     accesses++;
 161     int tmp_in_cache = 0;
 162     Addr blkAddr = blkAlign(addr);
 163     FALRUBlk* blk = hashLookup(blkAddr);
 164
 165     if (blk && blk->isValid()) {
 166         assert(blk->tag == blkAddr);
 167         tmp_in_cache = blk->inCache;
 168         for (int i = 0; i < numCaches; i++) {
 169             if (1<<i & blk->inCache) {
 170                 hits[i]++;
 171             } else {
 172                 misses[i]++;
 173             }
 174         }
 175         hits[numCaches]++;
 176         if (blk != head){
 177             moveToHead(blk);
 178         }
 179     } else {
 180         blk = NULL;
 181         for (int i = 0; i < numCaches+1; ++i) {
 182             misses[i]++;
 183         }
 184     }
 185     if (inCache) {
 186         *inCache = tmp_in_cache;
 187     }
 188
 189     lat = hitLatency;
 190     //assert(check());
 191     return blk;
 192 }
 193
 194
 195 FALRUBlk*
 196 FALRU::findBlock(Addr addr) const
 197 {
 198     Addr blkAddr = blkAlign(addr);
 199     FALRUBlk* blk = hashLookup(blkAddr);
 200
 201     if (blk && blk->isValid()) {
 202         assert(blk->tag == blkAddr);
 203     } else {
 204         blk = NULL;
 205     }
 206     return blk;
 207 }
 208
 209 FALRUBlk*
 210 FALRU::findVictim(Addr addr, PacketList &writebacks)
 211 {
 212     FALRUBlk * blk = tail;
 213     assert(blk->inCache == 0);
 214     moveToHead(blk);
 215     tagHash.erase(blk->tag);
 216     tagHash[blkAlign(addr)] = blk;
 217     if (blk->isValid()) {
 218         replacements[0]++;
 219     } else {
 220         tagsInUse++;
 221         blk->isTouched = true;
 222         if (!warmedUp && tagsInUse.value() >= warmupBound) {
 223             warmedUp = true;
 224             warmupCycle = curTick;
 225         }
 226     }
 227     //assert(check());
 228     return blk;
 229 }
 230
 231 void
 232 FALRU::insertBlock(Addr addr, FALRU::BlkType *blk)
 233 {
 234 }
 235
 236 void
 237 FALRU::moveToHead(FALRUBlk *blk)
 238 {
 239     int updateMask = blk->inCache ^ cacheMask;
 240     for (int i = 0; i < numCaches; i++){
 241         if ((1<<i) & updateMask) {
 242             cacheBoundaries[i]->inCache &= ~(1<<i);
 243             cacheBoundaries[i] = cacheBoundaries[i]->prev;
 244         } else if (cacheBoundaries[i] == blk) {
 245             cacheBoundaries[i] = blk->prev;
 246         }
 247     }
 248     blk->inCache = cacheMask;
 249     if (blk != head) {
 250         if (blk == tail){
 251             assert(blk->next == NULL);
 252             tail = blk->prev;
 253             tail->next = NULL;
 254         } else {
 255             blk->prev->next = blk->next;
 256             blk->next->prev = blk->prev;
 257         }
 258         blk->next = head;
 259         blk->prev = NULL;
 260         head->prev = blk;
 261         head = blk;
 262     }
 263 }
 264
 265 bool
 266 FALRU::check()
 267 {
 268     FALRUBlk* blk = head;
 269     int size = 0;
 270     int boundary = 1<<17;
 271     int j = 0;
 272     int flags = cacheMask;
 273     while (blk) {
 274         size += blkSize;
 275         if (blk->inCache != flags) {
 276             return false;
 277         }
 278         if (size == boundary && blk != tail) {
 279             if (cacheBoundaries[j] != blk) {
 280                 return false;
 281             }
 282             flags &=~(1 << j);
 283             boundary = boundary<<1;
 284             ++j;
 285         }
 286         blk = blk->next;
 287     }
 288     return true;
 289 }