137 lines
4.8 KiB
C++
137 lines
4.8 KiB
C++
/*
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* Copyright (c) 2007 Mark D. Hill and David A. Wood
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* All rights reserved.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions are
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* met: redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer;
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* redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in the
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* documentation and/or other materials provided with the distribution;
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* neither the name of the copyright holders nor the names of its
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* contributors may be used to endorse or promote products derived from
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* this software without specific prior written permission.
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*
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* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
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* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
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* A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
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* OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
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* SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
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* LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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* DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
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* THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
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* OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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*/
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#ifndef __MEM_RUBY_SYSTEM_PSEUDOLRUPOLICY_HH__
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#define __MEM_RUBY_SYSTEM_PSEUDOLRUPOLICY_HH__
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#include "mem/ruby/system/AbstractReplacementPolicy.hh"
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/**
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* Implementation of tree-based pseudo-LRU replacement
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*
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* Works for any associativity between 1 and 128.
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*
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* Also implements associativities that are not a power of 2 by
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* ignoring paths that lead to a larger index (i.e. truncating the
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* tree). Note that when this occurs, the algorithm becomes less
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* fair, as it will favor indicies in the larger (by index) half of
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* the associative set. This is most unfair when the nearest power of
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* 2 is one below the associativy, and most fair when it is one above.
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*/
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class PseudoLRUPolicy : public AbstractReplacementPolicy
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{
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public:
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PseudoLRUPolicy(Index num_sets, Index assoc);
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~PseudoLRUPolicy();
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void touch(Index set, Index way, Time time);
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Index getVictim(Index set) const;
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private:
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unsigned int m_effective_assoc; /** nearest (to ceiling) power of 2 */
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unsigned int m_num_levels; /** number of levels in the tree */
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uint64* m_trees; /** bit representation of the
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* trees, one for each set */
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};
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inline
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PseudoLRUPolicy::PseudoLRUPolicy(Index num_sets, Index assoc)
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: AbstractReplacementPolicy(num_sets, assoc)
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{
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// associativity cannot exceed capacity of tree representation
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assert(num_sets > 0 && assoc > 1 && assoc <= (Index) sizeof(uint64)*4);
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m_trees = NULL;
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m_num_levels = 0;
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m_effective_assoc = 1;
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while (m_effective_assoc < assoc) {
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// effective associativity is ceiling power of 2
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m_effective_assoc <<= 1;
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}
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assoc = m_effective_assoc;
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while (true) {
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assoc /= 2;
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if(!assoc) break;
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m_num_levels++;
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}
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assert(m_num_levels < sizeof(unsigned int)*4);
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m_trees = new uint64[m_num_sets];
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for (unsigned i = 0; i < m_num_sets; i++) {
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m_trees[i] = 0;
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}
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}
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inline
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PseudoLRUPolicy::~PseudoLRUPolicy()
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{
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if (m_trees != NULL)
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delete[] m_trees;
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}
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inline void
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PseudoLRUPolicy::touch(Index set, Index index, Time time)
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{
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assert(index >= 0 && index < m_assoc);
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assert(set >= 0 && set < m_num_sets);
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int tree_index = 0;
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int node_val;
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for (int i = m_num_levels - 1; i >= 0; i--) {
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node_val = (index >> i)&1;
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if (node_val)
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m_trees[set] |= node_val << tree_index;
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else
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m_trees[set] &= ~(1 << tree_index);
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tree_index = node_val ? (tree_index*2)+2 : (tree_index*2)+1;
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}
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m_last_ref_ptr[set][index] = time;
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}
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inline Index
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PseudoLRUPolicy::getVictim(Index set) const
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{
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// assert(m_assoc != 0);
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Index index = 0;
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int tree_index = 0;
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int node_val;
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for (unsigned i = 0; i < m_num_levels; i++){
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node_val = (m_trees[set] >> tree_index) & 1;
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index += node_val ? 0 : (m_effective_assoc >> (i + 1));
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tree_index = node_val ? (tree_index * 2) + 1 : (tree_index * 2) + 2;
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}
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assert(index >= 0 && index < m_effective_assoc);
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/* return either the found index or the max possible index */
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/* NOTE: this is not a fair replacement when assoc is not a power of 2 */
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return (index > (m_assoc - 1)) ? m_assoc - 1 : index;
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}
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#endif // __MEM_RUBY_SYSTEM_PSEUDOLRUPOLICY_HH__
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