src/mem/packet_queue.cc

/*
 * Copyright (c) 2012 ARM Limited
 * All rights reserved.
 *
 * The license below extends only to copyright in the software and shall
 * not be construed as granting a license to any other intellectual
 * property including but not limited to intellectual property relating
 * to a hardware implementation of the functionality of the software
 * licensed hereunder.  You may use the software subject to the license
 * terms below provided that you ensure that this notice is replicated
 * unmodified and in its entirety in all distributions of the software,
 * modified or unmodified, in source code or in binary form.
 *
 * Copyright (c) 2006 The Regents of The University of Michigan
 * 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
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 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 *
 * Authors: Ali Saidi
 *          Andreas Hansson
 */

#include "debug/PacketQueue.hh"
#include "mem/packet_queue.hh"

using namespace std;

PacketQueue::PacketQueue(EventManager& _em, Port& _port,
                         const std::string _label)
    : em(_em), label(_label), sendEvent(this), drainEvent(NULL), port(_port),
      waitingOnRetry(false)
{
}

PacketQueue::~PacketQueue()
{
}

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

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

    DeferredPacketIterator i = transmitList.begin();
    DeferredPacketIterator end = transmitList.end();
    bool found = false;

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

    pkt->popLabel();

    return found;
}

void
PacketQueue::schedSendEvent(Tick when)
{
    // if we are waiting on a retry, do not schedule a send event, and
    // instead rely on retry being called
    if (waitingOnRetry) {
        assert(!sendEvent.scheduled());
        return;
    }

    if (!sendEvent.scheduled()) {
        em.schedule(&sendEvent, when);
    } else if (sendEvent.when() > when) {
        em.reschedule(&sendEvent, when);
    }
}

void
PacketQueue::schedSendTiming(PacketPtr pkt, Tick when)
{
    assert(when > curTick());

    // nothing on the list, or earlier than current front element,
    // schedule an event
    if (transmitList.empty() || when < transmitList.front().tick) {
        // note that currently we ignore a potentially outstanding retry
        // and could in theory put a new packet at the head of the
        // transmit list before retrying the existing packet
        transmitList.push_front(DeferredPacket(when, pkt));
        schedSendEvent(when);
        return;
    }

    // list is non-empty and this belongs at the end
    if (when >= transmitList.back().tick) {
        transmitList.push_back(DeferredPacket(when, pkt));
        return;
    }

    // this belongs in the middle somewhere, insertion sort
    DeferredPacketIterator i = transmitList.begin();
    ++i; // already checked for insertion at front
    while (i != transmitList.end() && when >= i->tick)
        ++i;
    transmitList.insert(i, DeferredPacket(when, pkt));
}

void PacketQueue::trySendTiming()
{
    assert(deferredPacketReady());

    // take the next packet off the list here, as we might return to
    // ourselves through the sendTiming call below
    DeferredPacket dp = transmitList.front();
    transmitList.pop_front();

    // attempt to send the packet and remember the outcome
    waitingOnRetry = !port.sendTiming(dp.pkt);

    if (waitingOnRetry) {
        // put the packet back at the front of the list (packet should
        // not have changed since it wasn't accepted)
        assert(!sendEvent.scheduled());
        transmitList.push_front(dp);
    }
}

void
PacketQueue::scheduleSend(Tick time)
{
    // the next ready time is either determined by the next deferred packet,
    // or in the cache through the MSHR ready time
    Tick nextReady = std::min(deferredPacketReadyTime(), time);

    if (nextReady != MaxTick) {
        // if the sendTiming caused someone else to call our
        // recvTiming we could already have an event scheduled, check
        if (!sendEvent.scheduled())
            em.schedule(&sendEvent, std::max(nextReady, curTick() + 1));
    } else {
        // no more to send, so if we're draining, we may be done
        if (drainEvent && !sendEvent.scheduled()) {
            drainEvent->process();
            drainEvent = NULL;
        }
    }
}

void
PacketQueue::sendDeferredPacket()
{
    // try to send what is on the list, this will set waitingOnRetry
    // accordingly
    trySendTiming();

    // if we succeeded and are not waiting for a retry, schedule the
    // next send
    if (!waitingOnRetry) {
        scheduleSend();
    }
}

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

unsigned int
PacketQueue::drain(Event *de)
{
    if (transmitList.empty() && !sendEvent.scheduled())
        return 0;
    drainEvent = de;
    return 1;
}