src/mem/cache/tags/compressed_tags.hh

   1 /*
   2  * Copyright (c) 2018 Inria
   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
  29 /**
  30  * @file
  31  * Declaration of a compressed set associative tag store using superblocks.
  32  */
  33
  34 #ifndef __MEM_CACHE_TAGS_COMPRESSED_TAGS_HH__
  35 #define __MEM_CACHE_TAGS_COMPRESSED_TAGS_HH__
  36
  37 #include <vector>
  38
  39 #include "mem/cache/tags/sector_tags.hh"
  40 #include "mem/cache/tags/super_blk.hh"
  41
  42 class BaseCache;
  43 class CacheBlk;
  44 struct CompressedTagsParams;
  45
  46 /**
  47  * A CompressedTags cache tag store.
  48  * @sa  \ref gem5MemorySystem "gem5 Memory System"
  49  *
  50  * The Compression Ratio (CR) of a superblock is defined by
  51  *     CR = uncompressed_size / compressed_size.
  52  *
  53  * The CompressedTags placement policy divides the cache into s sets of w
  54  * superblocks (ways). Each superblock can then contain up to CR compressed
  55  * blocks.
  56  *
  57  * For each tag entry there can be multiple data blocks. We have the same
  58  * number of tags a conventional cache would have, but we instantiate the
  59  * maximum number of data blocks (according to the compression ratio) per
  60  * tag, to virtually implement compression without increasing the complexity
  61  * of the simulator.
  62  *
  63  * This is a simple implementation of cache compression, where superblocks
  64  * can only have at most numBlocksPerSector compressed blocks, each compressed
  65  * to at least (100/numBlocksPerSector)% of its size.
  66  *
  67  * numBlocksPerSector holds the maximum number of blocks a superblock with
  68  * the best possible compression factor would hold. It is equivalent to CR
  69  * from the previous definition.
  70  */
  71 class CompressedTags : public SectorTags
  72 {
  73   private:
  74     /** The cache blocks. */
  75     std::vector<CompressionBlk> blks;
  76     /** The cache superblocks. */
  77     std::vector<SuperBlk> superBlks;
  78
  79   public:
  80     /** Convenience typedef. */
  81      typedef CompressedTagsParams Params;
  82
  83     /**
  84      * Construct and initialize this tag store.
  85      */
  86     CompressedTags(const Params *p);
  87
  88     /**
  89      * Destructor.
  90      */
  91     virtual ~CompressedTags() {};
  92
  93     /**
  94      * Initialize blocks as SuperBlk and CompressionBlk instances.
  95      */
  96     void tagsInit() override;
  97
  98     /**
  99      * Find replacement victim based on address. Checks if data can be co-
 100      * allocated before choosing blocks to be evicted.
 101      *
 102      * @param addr Address to find a victim for.
 103      * @param is_secure True if the target memory space is secure.
 104      * @param compressed_size Size, in bits, of new block to allocate.
 105      * @param evict_blks Cache blocks to be evicted.
 106      * @return Cache block to be replaced.
 107      */
 108     CacheBlk* findVictim(Addr addr, const bool is_secure,
 109                          const std::size_t compressed_size,
 110                          std::vector<CacheBlk*>& evict_blks) override;
 111
 112     /**
 113      * Insert the new block into the cache and update replacement data.
 114      *
 115      * @param pkt Packet holding the address to update
 116      * @param blk The block to update.
 117      */
 118     void insertBlock(const PacketPtr pkt, CacheBlk *blk) override;
 119
 120     /**
 121      * Visit each sub-block in the tags and apply a visitor.
 122      *
 123      * The visitor should be a std::function that takes a cache block.
 124      * reference as its parameter.
 125      *
 126      * @param visitor Visitor to call on each block.
 127      */
 128     void forEachBlk(std::function<void(CacheBlk &)> visitor) override;
 129
 130     /**
 131      * Find if any of the sub-blocks satisfies a condition.
 132      *
 133      * The visitor should be a std::function that takes a cache block
 134      * reference as its parameter. The visitor will terminate the
 135      * traversal early if the condition is satisfied.
 136      *
 137      * @param visitor Visitor to call on each block.
 138      */
 139     bool anyBlk(std::function<bool(CacheBlk &)> visitor) override;
 140 };
 141
 142 #endif //__MEM_CACHE_TAGS_COMPRESSED_TAGS_HH__