src/mem/ruby/structures/PseudoLRUPolicy.cc

   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
  35 PseudoLRUPolicy::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) sizeof(uint64)*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[m_num_sets];
  59     for (unsigned i = 0; i < m_num_sets; i++) {
  60         m_trees[i] = 0;
  61     }
  62 }
  63
  64 PseudoLRUPolicy *
  65 PseudoLRUReplacementPolicyParams::create()
  66 {
  67     return new PseudoLRUPolicy(this);
  68 }
  69
  70
  71 PseudoLRUPolicy::~PseudoLRUPolicy()
  72 {
  73     if (m_trees != NULL)
  74         delete[] m_trees;
  75 }
  76
  77 void
  78 PseudoLRUPolicy::touch(int64 set, int64 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
  96 int64
  97 PseudoLRUPolicy::getVictim(int64 set) const
  98 {
  99     int64 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 }