compressed_tags.hh revision 13945:a573bed35a8b 
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 * Authors: Daniel Carvalho
29 */
30
31/**
32 * @file
33 * Declaration of a compressed set associative tag store using superblocks.
34 */
35
36#ifndef __MEM_CACHE_TAGS_COMPRESSED_TAGS_HH__
37#define __MEM_CACHE_TAGS_COMPRESSED_TAGS_HH__
38
39#include <vector>
40
41#include "mem/cache/tags/sector_tags.hh"
42#include "mem/cache/tags/super_blk.hh"
43
44class BaseCache;
45struct CompressedTagsParams;
46
47/**
48 * A CompressedTags cache tag store.
49 * @sa  \ref gem5MemorySystem "gem5 Memory System"
50 *
51 * The Compression Ratio (CR) of a superblock is defined by
52 *     CR = uncompressed_size / compressed_size.
53 *
54 * The CompressedTags placement policy divides the cache into s sets of w
55 * superblocks (ways). Each superblock can then contain up to CR compressed
56 * blocks.
57 *
58 * For each tag entry there can be multiple data blocks. We have the same
59 * number of tags a conventional cache would have, but we instantiate the
60 * maximum number of data blocks (according to the compression ratio) per
61 * tag, to virtually implement compression without increasing the complexity
62 * of the simulator.
63 *
64 * This is a simple implementation of cache compression, where superblocks
65 * can only have at most numBlocksPerSector compressed blocks, each compressed
66 * to at least (100/numBlocksPerSector)% of its size.
67 *
68 * numBlocksPerSector holds the maximum number of blocks a superblock with
69 * the best possible compression factor would hold. It is equivalent to CR
70 * from the previous definition.
71 */
72class CompressedTags : public SectorTags
73{
74  private:
75    /** The cache blocks. */
76    std::vector<CompressionBlk> blks;
77    /** The cache superblocks. */
78    std::vector<SuperBlk> superBlks;
79
80  public:
81    /** Convenience typedef. */
82     typedef CompressedTagsParams Params;
83
84    /**
85     * Construct and initialize this tag store.
86     */
87    CompressedTags(const Params *p);
88
89    /**
90     * Destructor.
91     */
92    virtual ~CompressedTags() {};
93
94    /**
95     * Initialize blocks as SuperBlk and CompressionBlk instances.
96     */
97    void tagsInit() override;
98
99    /**
100     * Insert the new block into the cache and update replacement data.
101     *
102     * @param pkt Packet holding the address to update
103     * @param blk The block to update.
104     */
105    void insertBlock(const PacketPtr pkt, CacheBlk *blk) override;
106
107    /**
108     * Visit each sub-block in the tags and apply a visitor.
109     *
110     * The visitor should be a std::function that takes a cache block.
111     * reference as its parameter.
112     *
113     * @param visitor Visitor to call on each block.
114     */
115    void forEachBlk(std::function<void(CacheBlk &)> visitor) override;
116
117    /**
118     * Find if any of the sub-blocks satisfies a condition.
119     *
120     * The visitor should be a std::function that takes a cache block
121     * reference as its parameter. The visitor will terminate the
122     * traversal early if the condition is satisfied.
123     *
124     * @param visitor Visitor to call on each block.
125     */
126    bool anyBlk(std::function<bool(CacheBlk &)> visitor) override;
127};
128
129#endif //__MEM_CACHE_TAGS_COMPRESSED_TAGS_HH__
130