gem5/src/mem/xbar.cc

/*
 * Copyright (c) 2011-2015, 2018-2020 ARM Limited
 * All rights reserved
 *
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 * 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
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 * 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
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 * neither the name of the copyright holders nor the names of its
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 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
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 * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
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 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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/**
 * @file
 * Definition of a crossbar object.
 */

#include "mem/xbar.hh"

#include "base/logging.hh"
#include "base/trace.hh"
#include "debug/AddrRanges.hh"
#include "debug/Drain.hh"
#include "debug/XBar.hh"

namespace gem5
{

BaseXBar::BaseXBar(const BaseXBarParams &p)
    : ClockedObject(p),
      frontendLatency(p.frontend_latency),
      forwardLatency(p.forward_latency),
      responseLatency(p.response_latency),
      headerLatency(p.header_latency),
      width(p.width),
      gotAddrRanges(p.port_default_connection_count +
                          p.port_mem_side_ports_connection_count, false),
      gotAllAddrRanges(false), defaultPortID(InvalidPortID),
      useDefaultRange(p.use_default_range),

      ADD_STAT(transDist, statistics::units::Count::get(),
               "Transaction distribution"),
      ADD_STAT(pktCount, statistics::units::Count::get(),
               "Packet count per connected requestor and responder"),
      ADD_STAT(pktSize, statistics::units::Byte::get(),
               "Cumulative packet size per connected requestor and responder")
{
}

BaseXBar::~BaseXBar()
{
    for (auto port: memSidePorts)
        delete port;

    for (auto port: cpuSidePorts)
        delete port;
}

Port &
BaseXBar::getPort(const std::string &if_name, PortID idx)
{
    if (if_name == "mem_side_ports" && idx < memSidePorts.size()) {
        // the memory-side ports index translates directly to the vector
        // position
        return *memSidePorts[idx];
    } else  if (if_name == "default") {
        return *memSidePorts[defaultPortID];
    } else if (if_name == "cpu_side_ports" && idx < cpuSidePorts.size()) {
        // the CPU-side ports index translates directly to the vector position
        return *cpuSidePorts[idx];
    } else {
        return ClockedObject::getPort(if_name, idx);
    }
}

void
BaseXBar::calcPacketTiming(PacketPtr pkt, Tick header_delay)
{
    // the crossbar will be called at a time that is not necessarily
    // coinciding with its own clock, so start by determining how long
    // until the next clock edge (could be zero)
    Tick offset = clockEdge() - curTick();

    // the header delay depends on the path through the crossbar, and
    // we therefore rely on the caller to provide the actual
    // value
    pkt->headerDelay += offset + header_delay;

    // note that we add the header delay to the existing value, and
    // align it to the crossbar clock

    // do a quick sanity check to ensure the timings are not being
    // ignored, note that this specific value may cause problems for
    // slower interconnects
    panic_if(pkt->headerDelay > sim_clock::as_int::us,
             "Encountered header delay exceeding 1 us\n");

    if (pkt->hasData()) {
        // the payloadDelay takes into account the relative time to
        // deliver the payload of the packet, after the header delay,
        // we take the maximum since the payload delay could already
        // be longer than what this parcitular crossbar enforces.
        pkt->payloadDelay = std::max<Tick>(pkt->payloadDelay,
                                           divCeil(pkt->getSize(), width) *
                                           clockPeriod());
    }

    // the payload delay is not paying for the clock offset as that is
    // already done using the header delay, and the payload delay is
    // also used to determine how long the crossbar layer is busy and
    // thus regulates throughput
}

template <typename SrcType, typename DstType>
BaseXBar::Layer<SrcType, DstType>::Layer(DstType& _port, BaseXBar& _xbar,
                                       const std::string& _name) :
    statistics::Group(&_xbar, _name.c_str()),
    port(_port), xbar(_xbar), _name(xbar.name() + "." + _name), state(IDLE),
    waitingForPeer(NULL), releaseEvent([this]{ releaseLayer(); }, name()),
    ADD_STAT(occupancy, statistics::units::Tick::get(), "Layer occupancy (ticks)"),
    ADD_STAT(utilization, statistics::units::Ratio::get(), "Layer utilization")
{
    occupancy
        .flags(statistics::nozero);

    utilization
        .precision(1)
        .flags(statistics::nozero);

    utilization = occupancy / simTicks;
}

template <typename SrcType, typename DstType>
void BaseXBar::Layer<SrcType, DstType>::occupyLayer(Tick until)
{
    // ensure the state is busy at this point, as the layer should
    // transition from idle as soon as it has decided to forward the
    // packet to prevent any follow-on calls to sendTiming seeing an
    // unoccupied layer
    assert(state == BUSY);

    // until should never be 0 as express snoops never occupy the layer
    assert(until != 0);
    xbar.schedule(releaseEvent, until);

    // account for the occupied ticks
    occupancy += until - curTick();

    DPRINTF(BaseXBar, "The crossbar layer is now busy from tick %d to %d\n",
            curTick(), until);
}

template <typename SrcType, typename DstType>
bool
BaseXBar::Layer<SrcType, DstType>::tryTiming(SrcType* src_port)
{
    // if we are in the retry state, we will not see anything but the
    // retrying port (or in the case of the snoop ports the snoop
    // response port that mirrors the actual CPU-side port) as we leave
    // this state again in zero time if the peer does not immediately
    // call the layer when receiving the retry

    // first we see if the layer is busy, next we check if the
    // destination port is already engaged in a transaction waiting
    // for a retry from the peer
    if (state == BUSY || waitingForPeer != NULL) {
        // the port should not be waiting already
        assert(std::find(waitingForLayer.begin(), waitingForLayer.end(),
                         src_port) == waitingForLayer.end());

        // put the port at the end of the retry list waiting for the
        // layer to be freed up (and in the case of a busy peer, for
        // that transaction to go through, and then the layer to free
        // up)
        waitingForLayer.push_back(src_port);
        return false;
    }

    state = BUSY;

    return true;
}

template <typename SrcType, typename DstType>
void
BaseXBar::Layer<SrcType, DstType>::succeededTiming(Tick busy_time)
{
    // we should have gone from idle or retry to busy in the tryTiming
    // test
    assert(state == BUSY);

    // occupy the layer accordingly
    occupyLayer(busy_time);
}

template <typename SrcType, typename DstType>
void
BaseXBar::Layer<SrcType, DstType>::failedTiming(SrcType* src_port,
                                              Tick busy_time)
{
    // ensure no one got in between and tried to send something to
    // this port
    assert(waitingForPeer == NULL);

    // if the source port is the current retrying one or not, we have
    // failed in forwarding and should track that we are now waiting
    // for the peer to send a retry
    waitingForPeer = src_port;

    // we should have gone from idle or retry to busy in the tryTiming
    // test
    assert(state == BUSY);

    // occupy the bus accordingly
    occupyLayer(busy_time);
}

template <typename SrcType, typename DstType>
void
BaseXBar::Layer<SrcType, DstType>::releaseLayer()
{
    // releasing the bus means we should now be idle
    assert(state == BUSY);
    assert(!releaseEvent.scheduled());

    // update the state
    state = IDLE;

    // bus layer is now idle, so if someone is waiting we can retry
    if (!waitingForLayer.empty()) {
        // there is no point in sending a retry if someone is still
        // waiting for the peer
        if (waitingForPeer == NULL)
            retryWaiting();
    } else if (waitingForPeer == NULL && drainState() == DrainState::Draining) {
        DPRINTF(Drain, "Crossbar done draining, signaling drain manager\n");
        //If we weren't able to drain before, do it now.
        signalDrainDone();
    }
}

template <typename SrcType, typename DstType>
void
BaseXBar::Layer<SrcType, DstType>::retryWaiting()
{
    // this should never be called with no one waiting
    assert(!waitingForLayer.empty());

    // we always go to retrying from idle
    assert(state == IDLE);

    // update the state
    state = RETRY;

    // set the retrying port to the front of the retry list and pop it
    // off the list
    SrcType* retryingPort = waitingForLayer.front();
    waitingForLayer.pop_front();

    // tell the port to retry, which in some cases ends up calling the
    // layer again
    sendRetry(retryingPort);

    // If the layer is still in the retry state, sendTiming wasn't
    // called in zero time (e.g. the cache does this when a writeback
    // is squashed)
    if (state == RETRY) {
        // update the state to busy and reset the retrying port, we
        // have done our bit and sent the retry
        state = BUSY;

        // occupy the crossbar layer until the next clock edge
        occupyLayer(xbar.clockEdge());
    }
}

template <typename SrcType, typename DstType>
void
BaseXBar::Layer<SrcType, DstType>::recvRetry()
{
    // we should never get a retry without having failed to forward
    // something to this port
    assert(waitingForPeer != NULL);

    // add the port where the failed packet originated to the front of
    // the waiting ports for the layer, this allows us to call retry
    // on the port immediately if the crossbar layer is idle
    waitingForLayer.push_front(waitingForPeer);

    // we are no longer waiting for the peer
    waitingForPeer = NULL;

    // if the layer is idle, retry this port straight away, if we
    // are busy, then simply let the port wait for its turn
    if (state == IDLE) {
        retryWaiting();
    } else {
        assert(state == BUSY);
    }
}

PortID
BaseXBar::findPort(AddrRange addr_range)
{
    // we should never see any address lookups before we've got the
    // ranges of all connected CPU-side-port modules
    assert(gotAllAddrRanges);

    // Check the address map interval tree
    auto i = portMap.contains(addr_range);
    if (i != portMap.end()) {
        return i->second;
    }

    // Check if this matches the default range
    if (useDefaultRange) {
        if (addr_range.isSubset(defaultRange)) {
            DPRINTF(AddrRanges, "  found addr %s on default\n",
                    addr_range.to_string());
            return defaultPortID;
        }
    } else if (defaultPortID != InvalidPortID) {
        DPRINTF(AddrRanges, "Unable to find destination for %s, "
                "will use default port\n", addr_range.to_string());
        return defaultPortID;
    }

    // we should use the range for the default port and it did not
    // match, or the default port is not set
    fatal("Unable to find destination for %s on %s\n", addr_range.to_string(),
          name());
}

/** Function called by the port when the crossbar is receiving a range change.*/
void
BaseXBar::recvRangeChange(PortID mem_side_port_id)
{
    DPRINTF(AddrRanges, "Received range change from cpu_side_ports %s\n",
            memSidePorts[mem_side_port_id]->getPeer());

    // remember that we got a range from this memory-side port and thus the
    // connected CPU-side-port module
    gotAddrRanges[mem_side_port_id] = true;

    // update the global flag
    if (!gotAllAddrRanges) {
        // take a logical AND of all the ports and see if we got
        // ranges from everyone
        gotAllAddrRanges = true;
        std::vector<bool>::const_iterator r = gotAddrRanges.begin();
        while (gotAllAddrRanges &&  r != gotAddrRanges.end()) {
            gotAllAddrRanges &= *r++;
        }
        if (gotAllAddrRanges)
            DPRINTF(AddrRanges, "Got address ranges from all responders\n");
    }

    // note that we could get the range from the default port at any
    // point in time, and we cannot assume that the default range is
    // set before the other ones are, so we do additional checks once
    // all ranges are provided
    if (mem_side_port_id == defaultPortID) {
        // only update if we are indeed checking ranges for the
        // default port since the port might not have a valid range
        // otherwise
        if (useDefaultRange) {
            AddrRangeList ranges = memSidePorts[mem_side_port_id]->
                                   getAddrRanges();

            if (ranges.size() != 1)
                fatal("Crossbar %s may only have a single default range",
                      name());

            defaultRange = ranges.front();
        }
    } else {
        // the ports are allowed to update their address ranges
        // dynamically, so remove any existing entries
        if (gotAddrRanges[mem_side_port_id]) {
            for (auto p = portMap.begin(); p != portMap.end(); ) {
                if (p->second == mem_side_port_id)
                    // erasing invalidates the iterator, so advance it
                    // before the deletion takes place
                    portMap.erase(p++);
                else
                    p++;
            }
        }

        AddrRangeList ranges = memSidePorts[mem_side_port_id]->
                               getAddrRanges();

        for (const auto& r: ranges) {
            DPRINTF(AddrRanges, "Adding range %s for id %d\n",
                    r.to_string(), mem_side_port_id);
            if (portMap.insert(r, mem_side_port_id) == portMap.end()) {
                PortID conflict_id = portMap.intersects(r)->second;
                fatal("%s has two ports responding within range "
                      "%s:\n\t%s\n\t%s\n",
                      name(),
                      r.to_string(),
                      memSidePorts[mem_side_port_id]->getPeer(),
                      memSidePorts[conflict_id]->getPeer());
            }
        }
    }

    // if we have received ranges from all our neighbouring CPU-side-port
    // modules, go ahead and tell our connected memory-side-port modules in
    // turn, this effectively assumes a tree structure of the system
    if (gotAllAddrRanges) {
        DPRINTF(AddrRanges, "Aggregating address ranges\n");
        xbarRanges.clear();

        // start out with the default range
        if (useDefaultRange) {
            if (!gotAddrRanges[defaultPortID])
                fatal("Crossbar %s uses default range, but none provided",
                      name());

            xbarRanges.push_back(defaultRange);
            DPRINTF(AddrRanges, "-- Adding default %s\n",
                    defaultRange.to_string());
        }

        // merge all interleaved ranges and add any range that is not
        // a subset of the default range
        std::vector<AddrRange> intlv_ranges;
        for (const auto& r: portMap) {
            // if the range is interleaved then save it for now
            if (r.first.interleaved()) {
                // if we already got interleaved ranges that are not
                // part of the same range, then first do a merge
                // before we add the new one
                if (!intlv_ranges.empty() &&
                    !intlv_ranges.back().mergesWith(r.first)) {
                    DPRINTF(AddrRanges, "-- Merging range from %d ranges\n",
                            intlv_ranges.size());
                    AddrRange merged_range(intlv_ranges);
                    // next decide if we keep the merged range or not
                    if (!(useDefaultRange &&
                          merged_range.isSubset(defaultRange))) {
                        xbarRanges.push_back(merged_range);
                        DPRINTF(AddrRanges, "-- Adding merged range %s\n",
                                merged_range.to_string());
                    }
                    intlv_ranges.clear();
                }
                intlv_ranges.push_back(r.first);
            } else {
                // keep the current range if not a subset of the default
                if (!(useDefaultRange &&
                      r.first.isSubset(defaultRange))) {
                    xbarRanges.push_back(r.first);
                    DPRINTF(AddrRanges, "-- Adding range %s\n",
                            r.first.to_string());
                }
            }
        }

        // if there is still interleaved ranges waiting to be merged,
        // go ahead and do it
        if (!intlv_ranges.empty()) {
            DPRINTF(AddrRanges, "-- Merging range from %d ranges\n",
                    intlv_ranges.size());
            AddrRange merged_range(intlv_ranges);
            if (!(useDefaultRange && merged_range.isSubset(defaultRange))) {
                xbarRanges.push_back(merged_range);
                DPRINTF(AddrRanges, "-- Adding merged range %s\n",
                        merged_range.to_string());
            }
        }

        // also check that no range partially intersects with the
        // default range, this has to be done after all ranges are set
        // as there are no guarantees for when the default range is
        // update with respect to the other ones
        if (useDefaultRange) {
            for (const auto& r: xbarRanges) {
                // see if the new range is partially
                // overlapping the default range
                if (r.intersects(defaultRange) &&
                    !r.isSubset(defaultRange))
                    fatal("Range %s intersects the "                    \
                          "default range of %s but is not a "           \
                          "subset\n", r.to_string(), name());
            }
        }

        // tell all our neighbouring memory-side ports that our address
        // ranges have changed
        for (const auto& port: cpuSidePorts)
            port->sendRangeChange();
    }
}

AddrRangeList
BaseXBar::getAddrRanges() const
{
    // we should never be asked without first having sent a range
    // change, and the latter is only done once we have all the ranges
    // of the connected devices
    assert(gotAllAddrRanges);

    // at the moment, this never happens, as there are no cycles in
    // the range queries and no devices on the memory side of a crossbar
    // (CPU, cache, bridge etc) actually care about the ranges of the
    // ports they are connected to

    DPRINTF(AddrRanges, "Received address range request\n");

    return xbarRanges;
}

void
BaseXBar::regStats()
{
    ClockedObject::regStats();

    using namespace statistics;

    transDist
        .init(MemCmd::NUM_MEM_CMDS)
        .flags(nozero);

    // get the string representation of the commands
    for (int i = 0; i < MemCmd::NUM_MEM_CMDS; i++) {
        MemCmd cmd(i);
        const std::string &cstr = cmd.toString();
        transDist.subname(i, cstr);
    }

    pktCount
        .init(cpuSidePorts.size(), memSidePorts.size())
        .flags(total | nozero | nonan);

    pktSize
        .init(cpuSidePorts.size(), memSidePorts.size())
        .flags(total | nozero | nonan);

    // both the packet count and total size are two-dimensional
    // vectors, indexed by CPU-side port id and memory-side port id, thus the
    // neighbouring memory-side ports and CPU-side ports, they do not
    // differentiate what came from the memory-side ports and was forwarded to
    // the CPU-side ports (requests and snoop responses) and what came from
    // the CPU-side ports and was forwarded to the memory-side ports (responses
    // and snoop requests)
    for (int i = 0; i < cpuSidePorts.size(); i++) {
        pktCount.subname(i, cpuSidePorts[i]->getPeer().name());
        pktSize.subname(i, cpuSidePorts[i]->getPeer().name());
        for (int j = 0; j < memSidePorts.size(); j++) {
            pktCount.ysubname(j, memSidePorts[j]->getPeer().name());
            pktSize.ysubname(j, memSidePorts[j]->getPeer().name());
        }
    }
}

template <typename SrcType, typename DstType>
DrainState
BaseXBar::Layer<SrcType, DstType>::drain()
{
    //We should check that we're not "doing" anything, and that noone is
    //waiting. We might be idle but have someone waiting if the device we
    //contacted for a retry didn't actually retry.
    if (state != IDLE) {
        DPRINTF(Drain, "Crossbar not drained\n");
        return DrainState::Draining;
    } else {
        return DrainState::Drained;
    }
}

/**
 * Crossbar layer template instantiations. Could be removed with _impl.hh
 * file, but since there are only two given options (RequestPort and
 * ResponsePort) it seems a bit excessive at this point.
 */
template class BaseXBar::Layer<ResponsePort, RequestPort>;
template class BaseXBar::Layer<RequestPort, ResponsePort>;

} // namespace gem5