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/*
* Copyright (c) 2007 Mark D. Hill and David A. Wood
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions are
* met: redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer;
* redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution;
* neither the name of the copyright holders nor the names of its
* contributors may be used to endorse or promote products derived from
* this software without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
* A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
* OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
* SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
* LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
* DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
* THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
* OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/
#ifndef __MEM_RUBY_SYSTEM_PSEUDOLRUPOLICY_HH__
#define __MEM_RUBY_SYSTEM_PSEUDOLRUPOLICY_HH__
#include "mem/ruby/structures/AbstractReplacementPolicy.hh"
/**
* Implementation of tree-based pseudo-LRU replacement
*
* Works for any associativity between 1 and 128.
*
* Also implements associativities that are not a power of 2 by
* ignoring paths that lead to a larger index (i.e. truncating the
* tree). Note that when this occurs, the algorithm becomes less
* fair, as it will favor indicies in the larger (by index) half of
* the associative set. This is most unfair when the nearest power of
* 2 is one below the associativy, and most fair when it is one above.
*/
class PseudoLRUPolicy : public AbstractReplacementPolicy
{
public:
PseudoLRUPolicy(int64 num_sets, int64 assoc);
~PseudoLRUPolicy();
void touch(int64 set, int64 way, Tick time);
int64 getVictim(int64 set) const;
private:
unsigned int m_effective_assoc; /** nearest (to ceiling) power of 2 */
unsigned int m_num_levels; /** number of levels in the tree */
uint64* m_trees; /** bit representation of the
* trees, one for each set */
};
inline
PseudoLRUPolicy::PseudoLRUPolicy(int64 num_sets, int64 assoc)
: AbstractReplacementPolicy(num_sets, assoc)
{
// associativity cannot exceed capacity of tree representation
assert(num_sets > 0 && assoc > 1 && assoc <= sizeof(uint64)*4);
m_trees = NULL;
m_num_levels = 0;
m_effective_assoc = 1;
while (m_effective_assoc < assoc) {
// effective associativity is ceiling power of 2
m_effective_assoc <<= 1;
}
assoc = m_effective_assoc;
while (true) {
assoc /= 2;
if(!assoc) break;
m_num_levels++;
}
assert(m_num_levels < sizeof(unsigned int)*4);
m_trees = new uint64[m_num_sets];
for (unsigned i = 0; i < m_num_sets; i++) {
m_trees[i] = 0;
}
}
inline
PseudoLRUPolicy::~PseudoLRUPolicy()
{
if (m_trees != NULL)
delete[] m_trees;
}
inline void
PseudoLRUPolicy::touch(int64 set, int64 index, Tick time)
{
assert(index >= 0 && index < m_assoc);
assert(set >= 0 && set < m_num_sets);
int tree_index = 0;
int node_val;
for (int i = m_num_levels - 1; i >= 0; i--) {
node_val = (index >> i)&1;
if (node_val)
m_trees[set] |= node_val << tree_index;
else
m_trees[set] &= ~(1 << tree_index);
tree_index = node_val ? (tree_index*2)+2 : (tree_index*2)+1;
}
m_last_ref_ptr[set][index] = time;
}
inline int64
PseudoLRUPolicy::getVictim(int64 set) const
{
// assert(m_assoc != 0);
int64 index = 0;
int tree_index = 0;
int node_val;
for (unsigned i = 0; i < m_num_levels; i++){
node_val = (m_trees[set] >> tree_index) & 1;
index += node_val ? 0 : (m_effective_assoc >> (i + 1));
tree_index = node_val ? (tree_index * 2) + 1 : (tree_index * 2) + 2;
}
assert(index >= 0 && index < m_effective_assoc);
/* return either the found index or the max possible index */
/* NOTE: this is not a fair replacement when assoc is not a power of 2 */
return (index > (m_assoc - 1)) ? m_assoc - 1 : index;
}
#endif // __MEM_RUBY_SYSTEM_PSEUDOLRUPOLICY_HH__
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