PseudoLRUPolicy.cc revision 11030:17240f381d6a 
1/*
2 * Copyright (c) 2013 Advanced Micro Devices, Inc
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 * Author: Derek Hower
29 */
30
31#include "mem/ruby/structures/PseudoLRUPolicy.hh"
32
33
34
35PseudoLRUPolicy::PseudoLRUPolicy(const Params * p)
36    : AbstractReplacementPolicy(p)
37{
38    // associativity cannot exceed capacity of tree representation
39    assert(m_num_sets > 0 &&
40           m_assoc > 1 &&
41           m_assoc <= (int64_t) sizeof(uint64_t)*4);
42
43    m_trees = NULL;
44    m_num_levels = 0;
45
46    m_effective_assoc = 1;
47    while (m_effective_assoc < m_assoc) {
48        // effective associativity is ceiling power of 2
49        m_effective_assoc <<= 1;
50    }
51    int tmp_assoc = m_effective_assoc;
52    while (true) {
53        tmp_assoc /= 2;
54        if(!tmp_assoc) break;
55        m_num_levels++;
56    }
57    assert(m_num_levels < sizeof(unsigned int)*4);
58    m_trees = new uint64_t[m_num_sets];
59    for (unsigned i = 0; i < m_num_sets; i++) {
60        m_trees[i] = 0;
61    }
62}
63
64PseudoLRUPolicy *
65PseudoLRUReplacementPolicyParams::create()
66{
67    return new PseudoLRUPolicy(this);
68}
69
70
71PseudoLRUPolicy::~PseudoLRUPolicy()
72{
73    if (m_trees != NULL)
74        delete[] m_trees;
75}
76
77void
78PseudoLRUPolicy::touch(int64_t set, int64_t index, Tick time)
79{
80    assert(index >= 0 && index < m_assoc);
81    assert(set >= 0 && set < m_num_sets);
82
83    int tree_index = 0;
84    int node_val;
85    for (int i = m_num_levels - 1; i >= 0; i--) {
86        node_val = (index >> i)&1;
87        if (node_val)
88            m_trees[set] |= node_val << tree_index;
89        else
90            m_trees[set] &= ~(1 << tree_index);
91        tree_index = node_val ? (tree_index*2)+2 : (tree_index*2)+1;
92    }
93    m_last_ref_ptr[set][index] = time;
94}
95
96int64_t
97PseudoLRUPolicy::getVictim(int64_t set) const
98{
99    int64_t index = 0;
100
101    int tree_index = 0;
102    int node_val;
103    for (unsigned i = 0; i < m_num_levels; i++){
104        node_val = (m_trees[set] >> tree_index) & 1;
105        index += node_val ? 0 : (m_effective_assoc >> (i + 1));
106        tree_index = node_val ? (tree_index * 2) + 1 : (tree_index * 2) + 2;
107    }
108    assert(index >= 0 && index < m_effective_assoc);
109
110    /* return either the found index or the max possible index */
111    /* NOTE: this is not a fair replacement when assoc is not a power of 2 */
112    return (index > (m_assoc - 1)) ? m_assoc - 1 : index;
113}
114