src/mem/cache/replacement_policies/random_rp.cc

/**
 * Copyright (c) 2018 Inria
 * 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
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 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

#include "mem/cache/replacement_policies/random_rp.hh"

#include <cassert>
#include <memory>

#include "base/random.hh"
#include "params/RandomRP.hh"

RandomRP::RandomRP(const Params *p)
    : BaseReplacementPolicy(p)
{
}

void
RandomRP::invalidate(const std::shared_ptr<ReplacementData>& replacement_data)
const
{
    // Unprioritize replacement data victimization
    std::static_pointer_cast<RandomReplData>(
        replacement_data)->valid = false;
}

void
RandomRP::touch(const std::shared_ptr<ReplacementData>& replacement_data) const
{
}

void
RandomRP::reset(const std::shared_ptr<ReplacementData>& replacement_data) const
{
    // Unprioritize replacement data victimization
    std::static_pointer_cast<RandomReplData>(
        replacement_data)->valid = true;
}

ReplaceableEntry*
RandomRP::getVictim(const ReplacementCandidates& candidates) const
{
    // There must be at least one replacement candidate
    assert(candidates.size() > 0);

    // Choose one candidate at random
    ReplaceableEntry* victim = candidates[random_mt.random<unsigned>(0,
                                    candidates.size() - 1)];

    // Visit all candidates to search for an invalid entry. If one is found,
    // its eviction is prioritized
    for (const auto& candidate : candidates) {
        if (!std::static_pointer_cast<RandomReplData>(
                    candidate->replacementData)->valid) {
            victim = candidate;
            break;
        }
    }

    return victim;
}

std::shared_ptr<ReplacementData>
RandomRP::instantiateEntry()
{
    return std::shared_ptr<ReplacementData>(new RandomReplData());
}

RandomRP*
RandomRPParams::create()
{
    return new RandomRP(this);
}