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
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 *
 * Authors: Daniel Carvalho
 */

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

#include "base/random.hh"
#include "debug/CacheRepl.hh"

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

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

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

    // Visit all candidates to find an invalid entry
    for (const auto& candidate : candidates) {
        // Give priority to victimise invalid entries
        if (!candidate->isValid()){
            blk = candidate;
            break;
        }
    }

    // If no invalid blocks were found, choose one of the candidates randomly
    DPRINTF(CacheRepl, "set %x, way %x: selecting blk for replacement\n",
            blk->set, blk->way);

    return blk;
}

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