xref: /gem5/src/mem/cache/tags/indexing_policies/set_associative.hh

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 * Authors: Daniel Carvalho
 *          Erik Hallnor
 */

/**
 * @file
 * Declaration of a set associative indexing policy.
 */

#ifndef __MEM_CACHE_INDEXING_POLICIES_SET_ASSOCIATIVE_HH__
#define __MEM_CACHE_INDEXING_POLICIES_SET_ASSOCIATIVE_HH__

#include <vector>

#include "mem/cache/tags/indexing_policies/base.hh"
#include "params/SetAssociative.hh"

class ReplaceableEntry;

/**
 * A set associative indexing policy.
 * @sa  \ref gem5MemorySystem "gem5 Memory System"
 *
 * The set associative indexing policy has an immutable/identity mapping, so a
 * value x is always mapped to set x, independent of the way, that is,
 * Hash(A, 0) = Hash(A, 1) = Hash(A, N-1), where N is the number of ways.
 *
 * For example, let's assume address A maps to set 3 on way 0. This policy
 * makes so that A is also mappable to set 3 on every other way. Visually, the
 * possible locations of A are, for a table with 4 ways and 8 sets:
 *    Way 0   1   2   3
 *  Set   _   _   _   _
 *    0  |_| |_| |_| |_|
 *    1  |_| |_| |_| |_|
 *    2  |_| |_| |_| |_|
 *    3  |X| |X| |X| |X|
 *    4  |_| |_| |_| |_|
 *    5  |_| |_| |_| |_|
 *    6  |_| |_| |_| |_|
 *    7  |_| |_| |_| |_|
 */
class SetAssociative : public BaseIndexingPolicy
{
  private:
    /**
     * Apply a hash function to calculate address set.
     *
     * @param addr The address to calculate the set for.
     * @return The set index for given combination of address and way.
     */
    uint32_t extractSet(const Addr addr) const;

  public:
    /**
     * Convenience typedef.
     */
    typedef SetAssociativeParams Params;

    /**
     * Construct and initialize this policy.
     */
    SetAssociative(const Params *p);

    /**
     * Destructor.
     */
    ~SetAssociative() {};

    /**
     * Find all possible entries for insertion and replacement of an address.
     * Should be called immediately before ReplacementPolicy's findVictim()
     * not to break cache resizing.
     * Returns entries in all ways belonging to the set of the address.
     *
     * @param addr The addr to a find possible entries for.
     * @return The possible entries.
     */
    std::vector<ReplaceableEntry*> getPossibleEntries(const Addr addr) const
                                                                     override;

    /**
     * Regenerate an entry's address from its tag and assigned set and way.
     *
     * @param tag The tag bits.
     * @param entry The entry.
     * @return the entry's original addr value.
     */
    Addr regenerateAddr(const Addr tag, const ReplaceableEntry* entry) const
                                                                   override;
};

#endif //__MEM_CACHE_INDEXING_POLICIES_SET_ASSOCIATIVE_HH__