gem5/src/mem/cache/tags/lru.cc

/*
 * Copyright (c) 2012 ARM Limited
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 * Authors: Erik Hallnor
 */

/**
 * @file
 * Definitions of LRU tag store.
 */

#include <string>

#include "base/intmath.hh"
#include "debug/Cache.hh"
#include "debug/CacheRepl.hh"
#include "mem/cache/tags/cacheset.hh"
#include "mem/cache/tags/lru.hh"
#include "mem/cache/base.hh"
#include "sim/core.hh"

using namespace std;

// create and initialize a LRU/MRU cache structure
LRU::LRU(unsigned _numSets, unsigned _blkSize, unsigned _assoc,
         unsigned _hit_latency)
    : numSets(_numSets), blkSize(_blkSize), assoc(_assoc),
      hitLatency(_hit_latency)
{
    // Check parameters
    if (blkSize < 4 || !isPowerOf2(blkSize)) {
        fatal("Block size must be at least 4 and a power of 2");
    }
    if (numSets <= 0 || !isPowerOf2(numSets)) {
        fatal("# of sets must be non-zero and a power of 2");
    }
    if (assoc <= 0) {
        fatal("associativity must be greater than zero");
    }
    if (hitLatency <= 0) {
        fatal("access latency must be greater than zero");
    }

    blkMask = blkSize - 1;
    setShift = floorLog2(blkSize);
    setMask = numSets - 1;
    tagShift = setShift + floorLog2(numSets);
    warmedUp = false;
    /** @todo Make warmup percentage a parameter. */
    warmupBound = numSets * assoc;

    sets = new CacheSet[numSets];
    blks = new BlkType[numSets * assoc];
    // allocate data storage in one big chunk
    numBlocks = numSets * assoc;
    dataBlks = new uint8_t[numBlocks * blkSize];

    unsigned blkIndex = 0;       // index into blks array
    for (unsigned i = 0; i < numSets; ++i) {
        sets[i].assoc = assoc;

        sets[i].blks = new BlkType*[assoc];

        // link in the data blocks
        for (unsigned j = 0; j < assoc; ++j) {
            // locate next cache block
            BlkType *blk = &blks[blkIndex];
            blk->data = &dataBlks[blkSize*blkIndex];
            ++blkIndex;

            // invalidate new cache block
            blk->invalidate();

            //EGH Fix Me : do we need to initialize blk?

            // Setting the tag to j is just to prevent long chains in the hash
            // table; won't matter because the block is invalid
            blk->tag = j;
            blk->whenReady = 0;
            blk->isTouched = false;
            blk->size = blkSize;
            sets[i].blks[j]=blk;
            blk->set = i;
        }
    }
}

LRU::~LRU()
{
    delete [] dataBlks;
    delete [] blks;
    delete [] sets;
}

LRU::BlkType*
LRU::accessBlock(Addr addr, Cycles &lat, int master_id)
{
    Addr tag = extractTag(addr);
    unsigned set = extractSet(addr);
    BlkType *blk = sets[set].findBlk(tag);
    lat = hitLatency;
    if (blk != NULL) {
        // move this block to head of the MRU list
        sets[set].moveToHead(blk);
        DPRINTF(CacheRepl, "set %x: moving blk %x to MRU\n",
                set, regenerateBlkAddr(tag, set));
        if (blk->whenReady > curTick()
            && cache->ticksToCycles(blk->whenReady - curTick()) > hitLatency) {
            lat = cache->ticksToCycles(blk->whenReady - curTick());
        }
        blk->refCount += 1;
    }

    return blk;
}


LRU::BlkType*
LRU::findBlock(Addr addr) const
{
    Addr tag = extractTag(addr);
    unsigned set = extractSet(addr);
    BlkType *blk = sets[set].findBlk(tag);
    return blk;
}

LRU::BlkType*
LRU::findVictim(Addr addr, PacketList &writebacks)
{
    unsigned set = extractSet(addr);
    // grab a replacement candidate
    BlkType *blk = sets[set].blks[assoc-1];

    if (blk->isValid()) {
        DPRINTF(CacheRepl, "set %x: selecting blk %x for replacement\n",
                set, regenerateBlkAddr(blk->tag, set));
    }
    return blk;
}

void
LRU::insertBlock(Addr addr, BlkType *blk, int master_id)
{
    if (!blk->isTouched) {
        tagsInUse++;
        blk->isTouched = true;
        if (!warmedUp && tagsInUse.value() >= warmupBound) {
            warmedUp = true;
            warmupCycle = curTick();
        }
    }

    // If we're replacing a block that was previously valid update
    // stats for it. This can't be done in findBlock() because a
    // found block might not actually be replaced there if the
    // coherence protocol says it can't be.
    if (blk->isValid()) {
        replacements[0]++;
        totalRefs += blk->refCount;
        ++sampledRefs;
        blk->refCount = 0;

        // deal with evicted block
        assert(blk->srcMasterId < cache->system->maxMasters());
        occupancies[blk->srcMasterId]--;

        blk->invalidate();
    }

    blk->isTouched = true;
    // Set tag for new block.  Caller is responsible for setting status.
    blk->tag = extractTag(addr);

    // deal with what we are bringing in
    assert(master_id < cache->system->maxMasters());
    occupancies[master_id]++;
    blk->srcMasterId = master_id;

    unsigned set = extractSet(addr);
    sets[set].moveToHead(blk);
}

void
LRU::invalidate(BlkType *blk)
{
    assert(blk);
    assert(blk->isValid());
    tagsInUse--;
    assert(blk->srcMasterId < cache->system->maxMasters());
    occupancies[blk->srcMasterId]--;
    blk->srcMasterId = Request::invldMasterId;

    // should be evicted before valid blocks
    unsigned set = blk->set;
    sets[set].moveToTail(blk);
}

void
LRU::clearLocks()
{
    for (int i = 0; i < numBlocks; i++){
        blks[i].clearLoadLocks();
    }
}

std::string
LRU::print() const {
    std::string cache_state;
    for (unsigned i = 0; i < numSets; ++i) {
        // link in the data blocks
        for (unsigned j = 0; j < assoc; ++j) {
            BlkType *blk = sets[i].blks[j];
            if (blk->isValid())
                cache_state += csprintf("\tset: %d block: %d %s\n", i, j,
                        blk->print());
        }
    }
    if (cache_state.empty())
        cache_state = "no valid tags\n";
    return cache_state;
}

void
LRU::cleanupRefs()
{
    for (unsigned i = 0; i < numSets*assoc; ++i) {
        if (blks[i].isValid()) {
            totalRefs += blks[i].refCount;
            ++sampledRefs;
        }
    }
}