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