base.cc

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#include "mem/cache/prefetch/base.hh"
 
#include <cassert>
 
#include "base/intmath.hh"
#include "params/BasePrefetcher.hh"
#include "sim/system.hh"
 
namespace gem5
{
 
namespace prefetch
{
 
Base::PrefetchInfo::PrefetchInfo(PacketPtr pkt, Addr addr, bool miss)
  : address(addr), pc(pkt->req->hasPC() ? pkt->req->getPC() : 0),
    requestorId(pkt->req->requestorId()), validPC(pkt->req->hasPC()),
    secure(pkt->isSecure()), size(pkt->req->getSize()), write(pkt->isWrite()),
    paddress(pkt->req->getPaddr()), cacheMiss(miss)
{
    unsigned int req_size = pkt->req->getSize();
    if ((!write && miss) || !pkt->hasData()) {
        data = nullptr;
    } else {
        data = new uint8_t[req_size];
        Addr offset = pkt->req->getPaddr() - pkt->getAddr();
        std::memcpy(data, &(pkt->getConstPtr<uint8_t>()[offset]), req_size);
    }
}
 
Base::PrefetchInfo::PrefetchInfo(PrefetchInfo const &pfi, Addr addr)
  : address(addr), pc(pfi.pc), requestorId(pfi.requestorId),
    validPC(pfi.validPC), secure(pfi.secure), size(pfi.size),
    write(pfi.write), paddress(pfi.paddress), cacheMiss(pfi.cacheMiss),
    data(nullptr)
{
}
 
void
Base::PrefetchListener::notify(const CacheAccessProbeArg &arg)
{
    if (isFill) {
        parent.notifyFill(arg);
    } else {
        parent.probeNotify(arg, miss);
    }
}
 
void
Base::PrefetchEvictListener::notify(const EvictionInfo &info)
{
    if (info.newData.empty())
        parent.notifyEvict(info);
}
 
Base::Base(const BasePrefetcherParams &p)
    : ClockedObject(p), listeners(), system(nullptr), probeManager(nullptr),
      blkSize(p.block_size), lBlkSize(floorLog2(blkSize)),
      onMiss(p.on_miss), onRead(p.on_read),
      onWrite(p.on_write), onData(p.on_data), onInst(p.on_inst),
      requestorId(p.sys->getRequestorId(this)),
      pageBytes(p.page_bytes),
      prefetchOnAccess(p.prefetch_on_access),
      prefetchOnPfHit(p.prefetch_on_pf_hit),
      useVirtualAddresses(p.use_virtual_addresses),
      prefetchStats(this), issuedPrefetches(0),
      usefulPrefetches(0), mmu(nullptr)
{
}
 
void
Base::setParentInfo(System *sys, ProbeManager *pm, unsigned blk_size)
{
    assert(!system && !probeManager);
    system = sys;
    probeManager = pm;
    // If the cache has a different block size from the system's, save it
    blkSize = blk_size;
    lBlkSize = floorLog2(blkSize);
}
 
Base::StatGroup::StatGroup(statistics::Group *parent)
  : statistics::Group(parent),
    ADD_STAT(demandMshrMisses, statistics::units::Count::get(),
        "demands not covered by prefetchs"),
    ADD_STAT(pfIssued, statistics::units::Count::get(),
        "number of hwpf issued"),
    ADD_STAT(pfUnused, statistics::units::Count::get(),
             "number of HardPF blocks evicted w/o reference"),
    ADD_STAT(pfUseful, statistics::units::Count::get(),
        "number of useful prefetch"),
    ADD_STAT(pfUsefulButMiss, statistics::units::Count::get(),
        "number of hit on prefetch but cache block is not in an usable "
        "state"),
    ADD_STAT(accuracy, statistics::units::Count::get(),
        "accuracy of the prefetcher"),
    ADD_STAT(coverage, statistics::units::Count::get(),
    "coverage brought by this prefetcher"),
    ADD_STAT(pfHitInCache, statistics::units::Count::get(),
        "number of prefetches hitting in cache"),
    ADD_STAT(pfHitInMSHR, statistics::units::Count::get(),
        "number of prefetches hitting in a MSHR"),
    ADD_STAT(pfHitInWB, statistics::units::Count::get(),
        "number of prefetches hit in the Write Buffer"),
    ADD_STAT(pfLate, statistics::units::Count::get(),
        "number of late prefetches (hitting in cache, MSHR or WB)")
{
    using namespace statistics;
 
    pfUnused.flags(nozero);
 
    accuracy.flags(total);
    accuracy = pfUseful / pfIssued;
 
    coverage.flags(total);
    coverage = pfUseful / (pfUseful + demandMshrMisses);
 
    pfLate = pfHitInCache + pfHitInMSHR + pfHitInWB;
}
 
bool
Base::observeAccess(const PacketPtr &pkt, bool miss, bool prefetched) const
{
    bool fetch = pkt->req->isInstFetch();
    bool read = pkt->isRead();
    bool inv = pkt->isInvalidate();
 
    if (!miss) {
        if (prefetchOnPfHit)
            return prefetched;
        if (!prefetchOnAccess)
            return false;
    }
    if (pkt->req->isUncacheable()) return false;
    if (fetch && !onInst) return false;
    if (!fetch && !onData) return false;
    if (!fetch && read && !onRead) return false;
    if (!fetch && !read && !onWrite) return false;
    if (!fetch && !read && inv) return false;
    if (pkt->cmd == MemCmd::CleanEvict) return false;
 
    if (onMiss) {
        return miss;
    }
 
    return true;
}
 
bool
Base::samePage(Addr a, Addr b) const
{
    return roundDown(a, pageBytes) == roundDown(b, pageBytes);
}
 
Addr
Base::blockAddress(Addr a) const
{
    return a & ~((Addr)blkSize-1);
}
 
Addr
Base::blockIndex(Addr a) const
{
    return a >> lBlkSize;
}
 
Addr
Base::pageAddress(Addr a) const
{
    return roundDown(a, pageBytes);
}
 
Addr
Base::pageOffset(Addr a) const
{
    return a & (pageBytes - 1);
}
 
Addr
Base::pageIthBlockAddress(Addr page, uint32_t blockIndex) const
{
    return page + (blockIndex << lBlkSize);
}
 
void
Base::probeNotify(const CacheAccessProbeArg &acc, bool miss)
{
    const PacketPtr pkt = acc.pkt;
    const CacheAccessor &cache = acc.cache;
 
    // Don't notify prefetcher on SWPrefetch, cache maintenance
    // operations or for writes that we are coaslescing.
    if (pkt->cmd.isSWPrefetch()) return;
    if (pkt->req->isCacheMaintenance()) return;
    if (pkt->isCleanEviction()) return;
    if (pkt->isWrite() && cache.coalesce()) return;
    if (!pkt->req->hasPaddr()) {
        panic("Request must have a physical address");
    }
 
    bool has_been_prefetched =
        acc.cache.hasBeenPrefetched(pkt->getAddr(), pkt->isSecure(),
                                    requestorId);
    if (has_been_prefetched) {
        usefulPrefetches += 1;
        prefetchStats.pfUseful++;
        if (miss)
            // This case happens when a demand hits on a prefetched line
            // that's not in the requested coherency state.
            prefetchStats.pfUsefulButMiss++;
    }
 
    // Verify this access type is observed by prefetcher
    if (observeAccess(pkt, miss, has_been_prefetched)) {
        if (useVirtualAddresses && pkt->req->hasVaddr()) {
            PrefetchInfo pfi(pkt, pkt->req->getVaddr(), miss);
            notify(acc, pfi);
        } else if (!useVirtualAddresses) {
            PrefetchInfo pfi(pkt, pkt->req->getPaddr(), miss);
            notify(acc, pfi);
        }
    }
}
 
void
Base::regProbeListeners()
{
    if (listeners.empty() && probeManager != nullptr) {
        listeners.push_back(probeManager->connect<PrefetchListener>(
            *this, "Miss", false, true));
        listeners.push_back(probeManager->connect<PrefetchListener>(
            *this, "Fill", true, false));
        listeners.push_back(probeManager->connect<PrefetchListener>(
            *this, "Hit", false, false));
        listeners.push_back(probeManager->connect<PrefetchEvictListener>(
            *this, "Data Update"));
    }
}
 
void
Base::addEventProbe(SimObject *obj, const char *name)
{
    ProbeManager *pm = obj->getProbeManager();
    listeners.push_back(pm->connect<PrefetchListener>(*this, name));
}
 
void
Base::addMMU(BaseMMU *m)
{
    fatal_if(mmu != nullptr, "Only one MMU can be registered");
    mmu = m;
}
 
} // namespace prefetch
} // namespace gem5