gem5/src/mem/packet_queue.cc

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#include "mem/packet_queue.hh"

#include "base/trace.hh"
#include "debug/Drain.hh"
#include "debug/PacketQueue.hh"

namespace gem5
{

PacketQueue::PacketQueue(EventManager& _em, const std::string& _label,
                         const std::string& _sendEventName,
                         bool force_order,
                         bool disable_sanity_check)
    : em(_em), sendEvent([this]{ processSendEvent(); }, _sendEventName),
      _disableSanityCheck(disable_sanity_check),
      forceOrder(force_order),
      label(_label), waitingOnRetry(false)
{
}

PacketQueue::~PacketQueue()
{
}

void
PacketQueue::retry()
{
    DPRINTF(PacketQueue, "Queue %s received retry\n", name());
    assert(waitingOnRetry);
    waitingOnRetry = false;
    sendDeferredPacket();
}

bool
PacketQueue::checkConflict(const PacketPtr pkt, const int blk_size) const
{
    // caller is responsible for ensuring that all packets have the
    // same alignment
    for (const auto& p : transmitList) {
        if (p.pkt->matchBlockAddr(pkt, blk_size))
            return true;
    }
    return false;
}

bool
PacketQueue::trySatisfyFunctional(PacketPtr pkt)
{
    pkt->pushLabel(label);

    auto i = transmitList.begin();
    bool found = false;

    while (!found && i != transmitList.end()) {
        // If the buffered packet contains data, and it overlaps the
        // current packet, then update data
        found = pkt->trySatisfyFunctional(i->pkt);
        ++i;
    }

    pkt->popLabel();

    return found;
}

void
PacketQueue::schedSendTiming(PacketPtr pkt, Tick when)
{
    DPRINTF(PacketQueue, "%s for %s address %x size %d when %lu ord: %i\n",
            __func__, pkt->cmdString(), pkt->getAddr(), pkt->getSize(), when,
            forceOrder);

    // we can still send a packet before the end of this tick
    assert(when >= curTick());

    // express snoops should never be queued
    assert(!pkt->isExpressSnoop());

    // add a very basic sanity check on the port to ensure the
    // invisible buffer is not growing beyond reasonable limits
    if (!_disableSanityCheck && transmitList.size() > 1024) {
        panic("Packet queue %s has grown beyond 1024 packets\n",
              name());
    }

    // we should either have an outstanding retry, or a send event
    // scheduled, but there is an unfortunate corner case where the
    // x86 page-table walker and timing CPU send out a new request as
    // part of the receiving of a response (called by
    // PacketQueue::sendDeferredPacket), in which we end up calling
    // ourselves again before we had a chance to update waitingOnRetry
    // assert(waitingOnRetry || sendEvent.scheduled());

    // this belongs in the middle somewhere, so search from the end to
    // order by tick; however, if forceOrder is set, also make sure
    // not to re-order in front of some existing packet with the same
    // address
    auto it = transmitList.end();
    while (it != transmitList.begin()) {
        --it;
        if ((forceOrder && it->pkt->matchAddr(pkt)) || it->tick <= when) {
            // emplace inserts the element before the position pointed to by
            // the iterator, so advance it one step
            transmitList.emplace(++it, when, pkt);
            return;
        }
    }
    // either the packet list is empty or this has to be inserted
    // before every other packet
    transmitList.emplace_front(when, pkt);
    schedSendEvent(when);
}

void
PacketQueue::schedSendEvent(Tick when)
{
    // if we are waiting on a retry just hold off
    if (waitingOnRetry) {
        DPRINTF(PacketQueue, "Not scheduling send as waiting for retry\n");
        assert(!sendEvent.scheduled());
        return;
    }

    if (when != MaxTick) {
        // we cannot go back in time, and to be consistent we stick to
        // one tick in the future
        when = std::max(when, curTick() + 1);
        // @todo Revisit the +1

        if (!sendEvent.scheduled()) {
            em.schedule(&sendEvent, when);
        } else if (when < sendEvent.when()) {
            // if the new time is earlier than when the event
            // currently is scheduled, move it forward
            em.reschedule(&sendEvent, when);
        }
    } else {
        // we get a MaxTick when there is no more to send, so if we're
        // draining, we may be done at this point
        if (drainState() == DrainState::Draining &&
            transmitList.empty() && !sendEvent.scheduled()) {

            DPRINTF(Drain, "PacketQueue done draining,"
                    "processing drain event\n");
            signalDrainDone();
        }
    }
}

void
PacketQueue::sendDeferredPacket()
{
    // sanity checks
    assert(!waitingOnRetry);
    assert(deferredPacketReady());

    DeferredPacket dp = transmitList.front();

    // take the packet of the list before sending it, as sending of
    // the packet in some cases causes a new packet to be enqueued
    // (most notaly when responding to the timing CPU, leading to a
    // new request hitting in the L1 icache, leading to a new
    // response)
    transmitList.pop_front();

    // use the appropriate implementation of sendTiming based on the
    // type of queue
    waitingOnRetry = !sendTiming(dp.pkt);

    // if we succeeded and are not waiting for a retry, schedule the
    // next send
    if (!waitingOnRetry) {
        schedSendEvent(deferredPacketReadyTime());
    } else {
        // put the packet back at the front of the list
        transmitList.emplace_front(dp);
    }
}

void
PacketQueue::processSendEvent()
{
    assert(!waitingOnRetry);
    sendDeferredPacket();
}

DrainState
PacketQueue::drain()
{
    if (transmitList.empty()) {
        return DrainState::Drained;
    } else {
        DPRINTF(Drain, "PacketQueue not drained\n");
        return DrainState::Draining;
    }
}

ReqPacketQueue::ReqPacketQueue(EventManager& _em, RequestPort& _mem_side_port,
                               const std::string _label)
    : PacketQueue(_em, _label, name(_mem_side_port, _label)),
      memSidePort(_mem_side_port)
{
}

bool
ReqPacketQueue::sendTiming(PacketPtr pkt)
{
    return memSidePort.sendTimingReq(pkt);
}

SnoopRespPacketQueue::SnoopRespPacketQueue(EventManager& _em,
                                           RequestPort& _mem_side_port,
                                           bool force_order,
                                           const std::string _label)
    : PacketQueue(_em, _label, name(_mem_side_port, _label), force_order),
      memSidePort(_mem_side_port)
{
}

bool
SnoopRespPacketQueue::sendTiming(PacketPtr pkt)
{
    return memSidePort.sendTimingSnoopResp(pkt);
}

RespPacketQueue::RespPacketQueue(EventManager& _em,
                                 ResponsePort& _cpu_side_port,
                                 bool force_order,
                                 const std::string _label)
    : PacketQueue(_em, _label, name(_cpu_side_port, _label), force_order),
      cpuSidePort(_cpu_side_port)
{
}

bool
RespPacketQueue::sendTiming(PacketPtr pkt)
{
    return cpuSidePort.sendTimingResp(pkt);
}

} // namespace gem5