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 __LRU_HH__
  37 #define __LRU_HH__
  38
  39 #include <cstring>
  40 #include <list>
  41
  42 #include "mem/cache/blk.hh" // base class
  43 #include "mem/packet.hh" // for inlined functions
  44 #include <assert.h>
  45 #include "mem/cache/tags/base.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   protected:
  96     /** The number of sets in the cache. */
  97     const int numSets;
  98     /** The number of bytes in a block. */
  99     const int blkSize;
 100     /** The associativity of the cache. */
 101     const int assoc;
 102     /** The hit latency. */
 103     const int hitLatency;
 104
 105     /** The cache sets. */
 106     CacheSet *sets;
 107
 108     /** The cache blocks. */
 109     LRUBlk *blks;
 110     /** The data blocks, 1 per cache block. */
 111     uint8_t *dataBlks;
 112
 113     /** The amount to shift the address to get the set. */
 114     int setShift;
 115     /** The amount to shift the address to get the tag. */
 116     int tagShift;
 117     /** Mask out all bits that aren't part of the set index. */
 118     unsigned setMask;
 119     /** Mask out all bits that aren't part of the block offset. */
 120     unsigned blkMask;
 121
 122 public:
 123     /**
 124      * Construct and initialize this tag store.
 125      * @param _numSets The number of sets in the cache.
 126      * @param _blkSize The number of bytes in a block.
 127      * @param _assoc The associativity of the cache.
 128      * @param _hit_latency The latency in cycles for a hit.
 129      */
 130     LRU(int _numSets, int _blkSize,     int _assoc, int _hit_latency);
 131
 132     /**
 133      * Destructor
 134      */
 135     virtual ~LRU();
 136
 137     /**
 138      * Return the block size.
 139      * @return the block size.
 140      */
 141     int getBlockSize()
 142     {
 143         return blkSize;
 144     }
 145
 146     /**
 147      * Return the subblock size. In the case of LRU it is always the block
 148      * size.
 149      * @return The block size.
 150      */
 151     int getSubBlockSize()
 152     {
 153         return blkSize;
 154     }
 155
 156     /**
 157      * Invalidate the given block.
 158      * @param blk The block to invalidate.
 159      */
 160     void invalidateBlk(BlkType *blk);
 161
 162     /**
 163      * Access block and update replacement data.  May not succeed, in which case
 164      * NULL pointer is returned.  This has all the implications of a cache
 165      * access and should only be used as such. Returns the access latency as a side effect.
 166      * @param addr The address to find.
 167      * @param asid The address space ID.
 168      * @param lat The access latency.
 169      * @return Pointer to the cache block if found.
 170      */
 171     LRUBlk* accessBlock(Addr addr, int &lat);
 172
 173     /**
 174      * Finds the given address in the cache, do not update replacement data.
 175      * i.e. This is a no-side-effect find of a block.
 176      * @param addr The address to find.
 177      * @param asid The address space ID.
 178      * @return Pointer to the cache block if found.
 179      */
 180     LRUBlk* findBlock(Addr addr) const;
 181
 182     /**
 183      * Find a block to evict for the address provided.
 184      * @param addr The addr to a find a replacement candidate for.
 185      * @param writebacks List for any writebacks to be performed.
 186      * @return The candidate block.
 187      */
 188     LRUBlk* findVictim(Addr addr, PacketList &writebacks);
 189
 190     /**
 191      * Insert the new block into the cache.  For LRU this means inserting into
 192      * the MRU position of the set.
 193      * @param addr The address to update.
 194      * @param blk The block to update.
 195      */
 196      void insertBlock(Addr addr, BlkType *blk);
 197
 198     /**
 199      * Generate the tag from the given address.
 200      * @param addr The address to get the tag from.
 201      * @return The tag of the address.
 202      */
 203     Addr extractTag(Addr addr) const
 204     {
 205         return (addr >> tagShift);
 206     }
 207
 208     /**
 209      * Calculate the set index from the address.
 210      * @param addr The address to get the set from.
 211      * @return The set index of the address.
 212      */
 213     int extractSet(Addr addr) const
 214     {
 215         return ((addr >> setShift) & setMask);
 216     }
 217
 218     /**
 219      * Get the block offset from an address.
 220      * @param addr The address to get the offset of.
 221      * @return The block offset.
 222      */
 223     int extractBlkOffset(Addr addr) const
 224     {
 225         return (addr & blkMask);
 226     }
 227
 228     /**
 229      * Align an address to the block size.
 230      * @param addr the address to align.
 231      * @return The block address.
 232      */
 233     Addr blkAlign(Addr addr) const
 234     {
 235         return (addr & ~(Addr)blkMask);
 236     }
 237
 238     /**
 239      * Regenerate the block address from the tag.
 240      * @param tag The tag of the block.
 241      * @param set The set of the block.
 242      * @return The block address.
 243      */
 244     Addr regenerateBlkAddr(Addr tag, unsigned set) const
 245     {
 246         return ((tag << tagShift) | ((Addr)set << setShift));
 247     }
 248
 249     /**
 250      * Return the hit latency.
 251      * @return the hit latency.
 252      */
 253     int getHitLatency() const
 254     {
 255         return hitLatency;
 256     }
 257
 258     /**
 259      * Called at end of simulation to complete average block reference stats.
 260      */
 261     virtual void cleanupRefs();
 262 };
 263
 264 #endif