src/mem/cache/tags/lru.hh

   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  * Declaration of a LRU tag store.
  34  */
  35
  36 #ifndef __MEM_CACHE_TAGS_LRU_HH__
  37 #define __MEM_CACHE_TAGS_LRU_HH__
  38
  39 #include <cassert>
  40 #include <cstring>
  41 #include <list>
  42
  43 #include "mem/cache/blk.hh"
  44 #include "mem/cache/tags/base.hh"
  45 #include "mem/packet.hh"
  46
  47 class BaseCache;
  48
  49 /**
  50  * LRU cache block.
  51  */
  52 class LRUBlk : public CacheBlk {
  53   public:
  54     /** Has this block been touched? Used to aid calculation of warmup time. */
  55     bool isTouched;
  56 };
  57
  58 /**
  59  * An associative set of cache blocks.
  60  */
  61 class CacheSet
  62 {
  63   public:
  64     /** The associativity of this set. */
  65     int assoc;
  66
  67     /** Cache blocks in this set, maintained in LRU order 0 = MRU. */
  68     LRUBlk **blks;
  69
  70     /**
  71      * Find a block matching the tag in this set.
  72      * @param asid The address space ID.
  73      * @param tag The Tag to find.
  74      * @return Pointer to the block if found.
  75      */
  76     LRUBlk* findBlk(Addr tag) const;
  77
  78     /**
  79      * Move the given block to the head of the list.
  80      * @param blk The block to move.
  81      */
  82     void moveToHead(LRUBlk *blk);
  83 };
  84
  85 /**
  86  * A LRU cache tag store.
  87  */
  88 class LRU : public BaseTags
  89 {
  90   public:
  91     /** Typedef the block type used in this tag store. */
  92     typedef LRUBlk BlkType;
  93     /** Typedef for a list of pointers to the local block class. */
  94     typedef std::list<LRUBlk*> BlkList;
  95
  96   protected:
  97     /** The number of sets in the cache. */
  98     const unsigned numSets;
  99     /** The number of bytes in a block. */
 100     const unsigned blkSize;
 101     /** The associativity of the cache. */
 102     const unsigned assoc;
 103     /** The hit latency. */
 104     const unsigned hitLatency;
 105
 106     /** The cache sets. */
 107     CacheSet *sets;
 108
 109     /** The cache blocks. */
 110     LRUBlk *blks;
 111     /** The data blocks, 1 per cache block. */
 112     uint8_t *dataBlks;
 113
 114     /** The amount to shift the address to get the set. */
 115     int setShift;
 116     /** The amount to shift the address to get the tag. */
 117     int tagShift;
 118     /** Mask out all bits that aren't part of the set index. */
 119     unsigned setMask;
 120     /** Mask out all bits that aren't part of the block offset. */
 121     unsigned blkMask;
 122
 123 public:
 124     /**
 125      * Construct and initialize this tag store.
 126      * @param _numSets The number of sets in the cache.
 127      * @param _blkSize The number of bytes in a block.
 128      * @param _assoc The associativity of the cache.
 129      * @param _hit_latency The latency in cycles for a hit.
 130      */
 131     LRU(unsigned _numSets, unsigned _blkSize, unsigned _assoc,
 132         unsigned _hit_latency);
 133
 134     /**
 135      * Destructor
 136      */
 137     virtual ~LRU();
 138
 139     /**
 140      * Return the block size.
 141      * @return the block size.
 142      */
 143     unsigned
 144     getBlockSize() const
 145     {
 146         return blkSize;
 147     }
 148
 149     /**
 150      * Return the subblock size. In the case of LRU it is always the block
 151      * size.
 152      * @return The block size.
 153      */
 154     unsigned
 155     getSubBlockSize() const
 156     {
 157         return blkSize;
 158     }
 159
 160     /**
 161      * Invalidate the given block.
 162      * @param blk The block to invalidate.
 163      */
 164     void invalidateBlk(BlkType *blk);
 165
 166     /**
 167      * Access block and update replacement data.  May not succeed, in which case
 168      * NULL pointer is returned.  This has all the implications of a cache
 169      * access and should only be used as such. Returns the access latency as a side effect.
 170      * @param addr The address to find.
 171      * @param asid The address space ID.
 172      * @param lat The access latency.
 173      * @return Pointer to the cache block if found.
 174      */
 175     LRUBlk* accessBlock(Addr addr, int &lat, int context_src);
 176
 177     /**
 178      * Finds the given address in the cache, do not update replacement data.
 179      * i.e. This is a no-side-effect find of a block.
 180      * @param addr The address to find.
 181      * @param asid The address space ID.
 182      * @return Pointer to the cache block if found.
 183      */
 184     LRUBlk* findBlock(Addr addr) const;
 185
 186     /**
 187      * Find a block to evict for the address provided.
 188      * @param addr The addr to a find a replacement candidate for.
 189      * @param writebacks List for any writebacks to be performed.
 190      * @return The candidate block.
 191      */
 192     LRUBlk* findVictim(Addr addr, PacketList &writebacks);
 193
 194     /**
 195      * Insert the new block into the cache.  For LRU this means inserting into
 196      * the MRU position of the set.
 197      * @param addr The address to update.
 198      * @param blk The block to update.
 199      */
 200      void insertBlock(Addr addr, BlkType *blk, int context_src);
 201
 202     /**
 203      * Generate the tag from the given address.
 204      * @param addr The address to get the tag from.
 205      * @return The tag of the address.
 206      */
 207     Addr extractTag(Addr addr) const
 208     {
 209         return (addr >> tagShift);
 210     }
 211
 212     /**
 213      * Calculate the set index from the address.
 214      * @param addr The address to get the set from.
 215      * @return The set index of the address.
 216      */
 217     int extractSet(Addr addr) const
 218     {
 219         return ((addr >> setShift) & setMask);
 220     }
 221
 222     /**
 223      * Get the block offset from an address.
 224      * @param addr The address to get the offset of.
 225      * @return The block offset.
 226      */
 227     int extractBlkOffset(Addr addr) const
 228     {
 229         return (addr & blkMask);
 230     }
 231
 232     /**
 233      * Align an address to the block size.
 234      * @param addr the address to align.
 235      * @return The block address.
 236      */
 237     Addr blkAlign(Addr addr) const
 238     {
 239         return (addr & ~(Addr)blkMask);
 240     }
 241
 242     /**
 243      * Regenerate the block address from the tag.
 244      * @param tag The tag of the block.
 245      * @param set The set of the block.
 246      * @return The block address.
 247      */
 248     Addr regenerateBlkAddr(Addr tag, unsigned set) const
 249     {
 250         return ((tag << tagShift) | ((Addr)set << setShift));
 251     }
 252
 253     /**
 254      * Return the hit latency.
 255      * @return the hit latency.
 256      */
 257     int getHitLatency() const
 258     {
 259         return hitLatency;
 260     }
 261
 262     /**
 263      * Called at end of simulation to complete average block reference stats.
 264      */
 265     virtual void cleanupRefs();
 266 };
 267
 268 #endif // __MEM_CACHE_TAGS_LRU_HH__