1/* 2 * Copyright (c) 2007 Mark D. Hill and David A. Wood
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3 * Copyright (c) 2013 Advanced Micro Devices, Inc |
4 * All rights reserved. 5 * 6 * Redistribution and use in source and binary forms, with or without 7 * modification, are permitted provided that the following conditions are 8 * met: redistributions of source code must retain the above copyright 9 * notice, this list of conditions and the following disclaimer; 10 * redistributions in binary form must reproduce the above copyright 11 * notice, this list of conditions and the following disclaimer in the 12 * documentation and/or other materials provided with the distribution; 13 * neither the name of the copyright holders nor the names of its 14 * contributors may be used to endorse or promote products derived from 15 * this software without specific prior written permission. 16 * 17 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS 18 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT 19 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR 20 * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT 21 * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, 22 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT 23 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, 24 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY 25 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT 26 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE 27 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 28 */ 29 30#ifndef __MEM_RUBY_STRUCTURES_PSEUDOLRUPOLICY_HH__ 31#define __MEM_RUBY_STRUCTURES_PSEUDOLRUPOLICY_HH__ 32 33#include "mem/ruby/structures/AbstractReplacementPolicy.hh"
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34#include "params/PseudoLRUReplacementPolicy.hh" |
35 36/** 37 * Implementation of tree-based pseudo-LRU replacement 38 * 39 * Works for any associativity between 1 and 128. 40 * 41 * Also implements associativities that are not a power of 2 by 42 * ignoring paths that lead to a larger index (i.e. truncating the 43 * tree). Note that when this occurs, the algorithm becomes less 44 * fair, as it will favor indicies in the larger (by index) half of 45 * the associative set. This is most unfair when the nearest power of 46 * 2 is one below the associativy, and most fair when it is one above. 47 */ 48 49class PseudoLRUPolicy : public AbstractReplacementPolicy 50{ 51 public:
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50 PseudoLRUPolicy(int64 num_sets, int64 assoc);
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52 typedef PseudoLRUReplacementPolicyParams Params; 53 PseudoLRUPolicy(const Params * p); |
54 ~PseudoLRUPolicy(); 55 56 void touch(int64 set, int64 way, Tick time); 57 int64 getVictim(int64 set) const; 58 59 private: 60 unsigned int m_effective_assoc; /** nearest (to ceiling) power of 2 */ 61 unsigned int m_num_levels; /** number of levels in the tree */ 62 uint64* m_trees; /** bit representation of the 63 * trees, one for each set */ 64}; 65
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63inline
64PseudoLRUPolicy::PseudoLRUPolicy(int64 num_sets, int64 assoc)
65 : AbstractReplacementPolicy(num_sets, assoc)
66{
67 // associativity cannot exceed capacity of tree representation
68 assert(num_sets > 0 && assoc > 1 && assoc <= sizeof(uint64)*4);
69
70 m_trees = NULL;
71 m_num_levels = 0;
72
73 m_effective_assoc = 1;
74 while (m_effective_assoc < assoc) {
75 // effective associativity is ceiling power of 2
76 m_effective_assoc <<= 1;
77 }
78 assoc = m_effective_assoc;
79 while (true) {
80 assoc /= 2;
81 if(!assoc) break;
82 m_num_levels++;
83 }
84 assert(m_num_levels < sizeof(unsigned int)*4);
85 m_trees = new uint64[m_num_sets];
86 for (unsigned i = 0; i < m_num_sets; i++) {
87 m_trees[i] = 0;
88 }
89}
90
91inline
92PseudoLRUPolicy::~PseudoLRUPolicy()
93{
94 if (m_trees != NULL)
95 delete[] m_trees;
96}
97
98inline void
99PseudoLRUPolicy::touch(int64 set, int64 index, Tick time)
100{
101 assert(index >= 0 && index < m_assoc);
102 assert(set >= 0 && set < m_num_sets);
103
104 int tree_index = 0;
105 int node_val;
106 for (int i = m_num_levels - 1; i >= 0; i--) {
107 node_val = (index >> i)&1;
108 if (node_val)
109 m_trees[set] |= node_val << tree_index;
110 else
111 m_trees[set] &= ~(1 << tree_index);
112 tree_index = node_val ? (tree_index*2)+2 : (tree_index*2)+1;
113 }
114 m_last_ref_ptr[set][index] = time;
115}
116
117inline int64
118PseudoLRUPolicy::getVictim(int64 set) const
119{
120 // assert(m_assoc != 0);
121 int64 index = 0;
122
123 int tree_index = 0;
124 int node_val;
125 for (unsigned i = 0; i < m_num_levels; i++){
126 node_val = (m_trees[set] >> tree_index) & 1;
127 index += node_val ? 0 : (m_effective_assoc >> (i + 1));
128 tree_index = node_val ? (tree_index * 2) + 1 : (tree_index * 2) + 2;
129 }
130 assert(index >= 0 && index < m_effective_assoc);
131
132 /* return either the found index or the max possible index */
133 /* NOTE: this is not a fair replacement when assoc is not a power of 2 */
134 return (index > (m_assoc - 1)) ? m_assoc - 1 : index;
135}
136
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66#endif // __MEM_RUBY_STRUCTURES_PSEUDOLRUPOLICY_HH__
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