src/mem/cache/tags/base.cc

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/**
 * @file
 * Definitions of BaseTags.
 */

#include "mem/cache/tags/base.hh"

#include <cassert>

#include "base/types.hh"
#include "mem/cache/replacement_policies/replaceable_entry.hh"
#include "mem/cache/tags/indexing_policies/base.hh"
#include "mem/request.hh"
#include "sim/core.hh"
#include "sim/sim_exit.hh"
#include "sim/system.hh"

namespace gem5
{

BaseTags::BaseTags(const Params &p)
    : ClockedObject(p), blkSize(p.block_size), blkMask(blkSize - 1),
      size(p.size), lookupLatency(p.tag_latency),
      system(p.system), indexingPolicy(p.indexing_policy),
      warmupBound((p.warmup_percentage/100.0) * (p.size / p.block_size)),
      warmedUp(false), numBlocks(p.size / p.block_size),
      dataBlks(new uint8_t[p.size]), // Allocate data storage in one big chunk
      stats(*this)
{
    registerExitCallback([this]() { cleanupRefs(); });
}

ReplaceableEntry*
BaseTags::findBlockBySetAndWay(int set, int way) const
{
    return indexingPolicy->getEntry(set, way);
}

CacheBlk*
BaseTags::findBlock(Addr addr, bool is_secure) const
{
    // Extract block tag
    Addr tag = extractTag(addr);

    // Find possible entries that may contain the given address
    const std::vector<ReplaceableEntry*> entries =
        indexingPolicy->getPossibleEntries(addr);

    // Search for block
    for (const auto& location : entries) {
        CacheBlk* blk = static_cast<CacheBlk*>(location);
        if (blk->matchTag(tag, is_secure)) {
            return blk;
        }
    }

    // Did not find block
    return nullptr;
}

void
BaseTags::insertBlock(const PacketPtr pkt, CacheBlk *blk)
{
    assert(!blk->isValid());

    // Previous block, if existed, has been removed, and now we have
    // to insert the new one

    // Deal with what we are bringing in
    RequestorID requestor_id = pkt->req->requestorId();
    assert(requestor_id < system->maxRequestors());
    stats.occupancies[requestor_id]++;

    // Insert block with tag, src requestor id and task id
    blk->insert(extractTag(pkt->getAddr()), pkt->isSecure(), requestor_id,
                pkt->req->taskId());

    // Check if cache warm up is done
    if (!warmedUp && stats.tagsInUse.value() >= warmupBound) {
        warmedUp = true;
        stats.warmupTick = curTick();
    }

    // We only need to write into one tag and one data block.
    stats.tagAccesses += 1;
    stats.dataAccesses += 1;
}

void
BaseTags::moveBlock(CacheBlk *src_blk, CacheBlk *dest_blk)
{
    assert(!dest_blk->isValid());
    assert(src_blk->isValid());

    // Move src's contents to dest's
    *dest_blk = std::move(*src_blk);

    assert(dest_blk->isValid());
    assert(!src_blk->isValid());
}

Addr
BaseTags::extractTag(const Addr addr) const
{
    return indexingPolicy->extractTag(addr);
}

void
BaseTags::cleanupRefsVisitor(CacheBlk &blk)
{
    if (blk.isValid()) {
        stats.totalRefs += blk.getRefCount();
        ++stats.sampledRefs;
    }
}

void
BaseTags::cleanupRefs()
{
    forEachBlk([this](CacheBlk &blk) { cleanupRefsVisitor(blk); });
}

void
BaseTags::computeStatsVisitor(CacheBlk &blk)
{
    if (blk.isValid()) {
        const uint32_t task_id = blk.getTaskId();
        assert(task_id < context_switch_task_id::NumTaskId);
        stats.occupanciesTaskId[task_id]++;
        Tick age = blk.getAge();

        int age_index;
        if (age / sim_clock::as_int::us < 10) { // <10us
            age_index = 0;
        } else if (age / sim_clock::as_int::us < 100) { // <100us
            age_index = 1;
        } else if (age / sim_clock::as_int::ms < 1) { // <1ms
            age_index = 2;
        } else if (age / sim_clock::as_int::ms < 10) { // <10ms
            age_index = 3;
        } else
            age_index = 4; // >10ms

        stats.ageTaskId[task_id][age_index]++;
    }
}

void
BaseTags::computeStats()
{
    for (unsigned i = 0; i < context_switch_task_id::NumTaskId; ++i) {
        stats.occupanciesTaskId[i] = 0;
        for (unsigned j = 0; j < 5; ++j) {
            stats.ageTaskId[i][j] = 0;
        }
    }

    forEachBlk([this](CacheBlk &blk) { computeStatsVisitor(blk); });
}

std::string
BaseTags::print()
{
    std::string str;

    auto print_blk = [&str](CacheBlk &blk) {
        if (blk.isValid())
            str += csprintf("\tBlock: %s\n", blk.print());
    };
    forEachBlk(print_blk);

    if (str.empty())
        str = "no valid tags\n";

    return str;
}

BaseTags::BaseTagStats::BaseTagStats(BaseTags &_tags)
    : statistics::Group(&_tags),
    tags(_tags),

    ADD_STAT(tagsInUse, statistics::units::Rate<
                statistics::units::Tick, statistics::units::Count>::get(),
             "Average ticks per tags in use"),
    ADD_STAT(totalRefs, statistics::units::Count::get(),
             "Total number of references to valid blocks."),
    ADD_STAT(sampledRefs, statistics::units::Count::get(),
             "Sample count of references to valid blocks."),
    ADD_STAT(avgRefs, statistics::units::Rate<
                statistics::units::Count, statistics::units::Count>::get(),
             "Average number of references to valid blocks."),
    ADD_STAT(warmupTick, statistics::units::Tick::get(),
             "The tick when the warmup percentage was hit."),
    ADD_STAT(occupancies, statistics::units::Rate<
                statistics::units::Count, statistics::units::Tick>::get(),
             "Average occupied blocks per tick, per requestor"),
    ADD_STAT(avgOccs, statistics::units::Rate<
                statistics::units::Ratio, statistics::units::Tick>::get(),
             "Average percentage of cache occupancy"),
    ADD_STAT(occupanciesTaskId, statistics::units::Count::get(),
             "Occupied blocks per task id"),
    ADD_STAT(ageTaskId, statistics::units::Count::get(),
             "Occupied blocks per task id, per block age"),
    ADD_STAT(ratioOccsTaskId, statistics::units::Ratio::get(),
             "Ratio of occupied blocks and all blocks, per task id"),
    ADD_STAT(tagAccesses, statistics::units::Count::get(),
             "Number of tag accesses"),
    ADD_STAT(dataAccesses, statistics::units::Count::get(),
             "Number of data accesses")
{
}

void
BaseTags::BaseTagStats::regStats()
{
    using namespace statistics;

    statistics::Group::regStats();

    System *system = tags.system;

    avgRefs = totalRefs / sampledRefs;

    occupancies
        .init(system->maxRequestors())
        .flags(nozero | nonan)
        ;
    for (int i = 0; i < system->maxRequestors(); i++) {
        occupancies.subname(i, system->getRequestorName(i));
    }

    avgOccs.flags(nozero | total);
    for (int i = 0; i < system->maxRequestors(); i++) {
        avgOccs.subname(i, system->getRequestorName(i));
    }

    avgOccs = occupancies / statistics::constant(tags.numBlocks);

    occupanciesTaskId
        .init(context_switch_task_id::NumTaskId)
        .flags(nozero | nonan)
        ;

    ageTaskId
        .init(context_switch_task_id::NumTaskId, 5)
        .flags(nozero | nonan)
        ;

    ratioOccsTaskId.flags(nozero);

    ratioOccsTaskId = occupanciesTaskId / statistics::constant(tags.numBlocks);
}

void
BaseTags::BaseTagStats::preDumpStats()
{
    statistics::Group::preDumpStats();

    tags.computeStats();
}

} // namespace gem5