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/*
* Copyright (c) 2011-2016 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
* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
* OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*
* Authors: Ali Saidi
* Andreas Hansson
* William Wang
*/
/**
* @file
* Definition of a crossbar object.
*/
#include "mem/coherent_xbar.hh"
#include "base/misc.hh"
#include "base/trace.hh"
#include "debug/AddrRanges.hh"
#include "debug/CoherentXBar.hh"
#include "sim/system.hh"
CoherentXBar::CoherentXBar(const CoherentXBarParams *p)
: BaseXBar(p), system(p->system), snoopFilter(p->snoop_filter),
snoopResponseLatency(p->snoop_response_latency),
pointOfCoherency(p->point_of_coherency)
{
// create the ports based on the size of the master and slave
// vector ports, and the presence of the default port, the ports
// are enumerated starting from zero
for (int i = 0; i < p->port_master_connection_count; ++i) {
std::string portName = csprintf("%s.master[%d]", name(), i);
MasterPort* bp = new CoherentXBarMasterPort(portName, *this, i);
masterPorts.push_back(bp);
reqLayers.push_back(new ReqLayer(*bp, *this,
csprintf(".reqLayer%d", i)));
snoopLayers.push_back(new SnoopRespLayer(*bp, *this,
csprintf(".snoopLayer%d", i)));
}
// see if we have a default slave device connected and if so add
// our corresponding master port
if (p->port_default_connection_count) {
defaultPortID = masterPorts.size();
std::string portName = name() + ".default";
MasterPort* bp = new CoherentXBarMasterPort(portName, *this,
defaultPortID);
masterPorts.push_back(bp);
reqLayers.push_back(new ReqLayer(*bp, *this, csprintf(".reqLayer%d",
defaultPortID)));
snoopLayers.push_back(new SnoopRespLayer(*bp, *this,
csprintf(".snoopLayer%d",
defaultPortID)));
}
// create the slave ports, once again starting at zero
for (int i = 0; i < p->port_slave_connection_count; ++i) {
std::string portName = csprintf("%s.slave[%d]", name(), i);
QueuedSlavePort* bp = new CoherentXBarSlavePort(portName, *this, i);
slavePorts.push_back(bp);
respLayers.push_back(new RespLayer(*bp, *this,
csprintf(".respLayer%d", i)));
snoopRespPorts.push_back(new SnoopRespPort(*bp, *this));
}
clearPortCache();
}
CoherentXBar::~CoherentXBar()
{
for (auto l: reqLayers)
delete l;
for (auto l: respLayers)
delete l;
for (auto l: snoopLayers)
delete l;
for (auto p: snoopRespPorts)
delete p;
}
void
CoherentXBar::init()
{
BaseXBar::init();
// iterate over our slave ports and determine which of our
// neighbouring master ports are snooping and add them as snoopers
for (const auto& p: slavePorts) {
// check if the connected master port is snooping
if (p->isSnooping()) {
DPRINTF(AddrRanges, "Adding snooping master %s\n",
p->getMasterPort().name());
snoopPorts.push_back(p);
}
}
if (snoopPorts.empty())
warn("CoherentXBar %s has no snooping ports attached!\n", name());
// inform the snoop filter about the slave ports so it can create
// its own internal representation
if (snoopFilter)
snoopFilter->setSlavePorts(slavePorts);
}
bool
CoherentXBar::recvTimingReq(PacketPtr pkt, PortID slave_port_id)
{
// determine the source port based on the id
SlavePort *src_port = slavePorts[slave_port_id];
// remember if the packet is an express snoop
bool is_express_snoop = pkt->isExpressSnoop();
bool cache_responding = pkt->cacheResponding();
// for normal requests, going downstream, the express snoop flag
// and the cache responding flag should always be the same
assert(is_express_snoop == cache_responding);
// determine the destination based on the address
PortID master_port_id = findPort(pkt->getAddr());
// test if the crossbar should be considered occupied for the current
// port, and exclude express snoops from the check
if (!is_express_snoop && !reqLayers[master_port_id]->tryTiming(src_port)) {
DPRINTF(CoherentXBar, "%s: src %s packet %s BUSY\n", __func__,
src_port->name(), pkt->print());
return false;
}
DPRINTF(CoherentXBar, "%s: src %s packet %s\n", __func__,
src_port->name(), pkt->print());
// store size and command as they might be modified when
// forwarding the packet
unsigned int pkt_size = pkt->hasData() ? pkt->getSize() : 0;
unsigned int pkt_cmd = pkt->cmdToIndex();
// store the old header delay so we can restore it if needed
Tick old_header_delay = pkt->headerDelay;
// a request sees the frontend and forward latency
Tick xbar_delay = (frontendLatency + forwardLatency) * clockPeriod();
// set the packet header and payload delay
calcPacketTiming(pkt, xbar_delay);
// determine how long to be crossbar layer is busy
Tick packetFinishTime = clockEdge(Cycles(1)) + pkt->payloadDelay;
if (!system->bypassCaches()) {
assert(pkt->snoopDelay == 0);
// the packet is a memory-mapped request and should be
// broadcasted to our snoopers but the source
if (snoopFilter) {
// check with the snoop filter where to forward this packet
auto sf_res = snoopFilter->lookupRequest(pkt, *src_port);
// the time required by a packet to be delivered through
// the xbar has to be charged also with to lookup latency
// of the snoop filter
pkt->headerDelay += sf_res.second * clockPeriod();
DPRINTF(CoherentXBar, "%s: src %s packet %s SF size: %i lat: %i\n",
__func__, src_port->name(), pkt->print(),
sf_res.first.size(), sf_res.second);
if (pkt->isEviction()) {
// for block-evicting packets, i.e. writebacks and
// clean evictions, there is no need to snoop up, as
// all we do is determine if the block is cached or
// not, instead just set it here based on the snoop
// filter result
if (!sf_res.first.empty())
pkt->setBlockCached();
} else {
forwardTiming(pkt, slave_port_id, sf_res.first);
}
} else {
forwardTiming(pkt, slave_port_id);
}
// add the snoop delay to our header delay, and then reset it
pkt->headerDelay += pkt->snoopDelay;
pkt->snoopDelay = 0;
}
// set up a sensible starting point
bool success = true;
// remember if the packet will generate a snoop response by
// checking if a cache set the cacheResponding flag during the
// snooping above
const bool expect_snoop_resp = !cache_responding && pkt->cacheResponding();
bool expect_response = pkt->needsResponse() && !pkt->cacheResponding();
const bool sink_packet = sinkPacket(pkt);
// in certain cases the crossbar is responsible for responding
bool respond_directly = false;
// store the original address as an address mapper could possibly
// modify the address upon a sendTimingRequest
const Addr addr(pkt->getAddr());
if (sink_packet) {
DPRINTF(CoherentXBar, "%s: Not forwarding %s\n", __func__,
pkt->print());
} else {
// determine if we are forwarding the packet, or responding to
// it
if (!pointOfCoherency || pkt->isRead() || pkt->isWrite()) {
// if we are passing on, rather than sinking, a packet to
// which an upstream cache has committed to responding,
// the line was needs writable, and the responding only
// had an Owned copy, so we need to immidiately let the
// downstream caches know, bypass any flow control
if (pkt->cacheResponding()) {
pkt->setExpressSnoop();
}
// since it is a normal request, attempt to send the packet
success = masterPorts[master_port_id]->sendTimingReq(pkt);
} else {
// no need to forward, turn this packet around and respond
// directly
assert(pkt->needsResponse());
respond_directly = true;
assert(!expect_snoop_resp);
expect_response = false;
}
}
if (snoopFilter && !system->bypassCaches()) {
// Let the snoop filter know about the success of the send operation
snoopFilter->finishRequest(!success, addr, pkt->isSecure());
}
// check if we were successful in sending the packet onwards
if (!success) {
// express snoops should never be forced to retry
assert(!is_express_snoop);
// restore the header delay
pkt->headerDelay = old_header_delay;
DPRINTF(CoherentXBar, "%s: src %s packet %s RETRY\n", __func__,
src_port->name(), pkt->print());
// update the layer state and schedule an idle event
reqLayers[master_port_id]->failedTiming(src_port,
clockEdge(Cycles(1)));
} else {
// express snoops currently bypass the crossbar state entirely
if (!is_express_snoop) {
// if this particular request will generate a snoop
// response
if (expect_snoop_resp) {
// we should never have an exsiting request outstanding
assert(outstandingSnoop.find(pkt->req) ==
outstandingSnoop.end());
outstandingSnoop.insert(pkt->req);
// basic sanity check on the outstanding snoops
panic_if(outstandingSnoop.size() > 512,
"Outstanding snoop requests exceeded 512\n");
}
// remember where to route the normal response to
if (expect_response || expect_snoop_resp) {
assert(routeTo.find(pkt->req) == routeTo.end());
routeTo[pkt->req] = slave_port_id;
panic_if(routeTo.size() > 512,
"Routing table exceeds 512 packets\n");
}
// update the layer state and schedule an idle event
reqLayers[master_port_id]->succeededTiming(packetFinishTime);
}
// stats updates only consider packets that were successfully sent
pktCount[slave_port_id][master_port_id]++;
pktSize[slave_port_id][master_port_id] += pkt_size;
transDist[pkt_cmd]++;
if (is_express_snoop) {
snoops++;
snoopTraffic += pkt_size;
}
}
if (sink_packet)
// queue the packet for deletion
pendingDelete.reset(pkt);
if (respond_directly) {
assert(pkt->needsResponse());
assert(success);
pkt->makeResponse();
if (snoopFilter && !system->bypassCaches()) {
// let the snoop filter inspect the response and update its state
snoopFilter->updateResponse(pkt, *slavePorts[slave_port_id]);
}
Tick response_time = clockEdge() + pkt->headerDelay;
pkt->headerDelay = 0;
slavePorts[slave_port_id]->schedTimingResp(pkt, response_time);
}
return success;
}
bool
CoherentXBar::recvTimingResp(PacketPtr pkt, PortID master_port_id)
{
// determine the source port based on the id
MasterPort *src_port = masterPorts[master_port_id];
// determine the destination
const auto route_lookup = routeTo.find(pkt->req);
assert(route_lookup != routeTo.end());
const PortID slave_port_id = route_lookup->second;
assert(slave_port_id != InvalidPortID);
assert(slave_port_id < respLayers.size());
// test if the crossbar should be considered occupied for the
// current port
if (!respLayers[slave_port_id]->tryTiming(src_port)) {
DPRINTF(CoherentXBar, "%s: src %s packet %s BUSY\n", __func__,
src_port->name(), pkt->print());
return false;
}
DPRINTF(CoherentXBar, "%s: src %s packet %s\n", __func__,
src_port->name(), pkt->print());
// store size and command as they might be modified when
// forwarding the packet
unsigned int pkt_size = pkt->hasData() ? pkt->getSize() : 0;
unsigned int pkt_cmd = pkt->cmdToIndex();
// a response sees the response latency
Tick xbar_delay = responseLatency * clockPeriod();
// set the packet header and payload delay
calcPacketTiming(pkt, xbar_delay);
// determine how long to be crossbar layer is busy
Tick packetFinishTime = clockEdge(Cycles(1)) + pkt->payloadDelay;
if (snoopFilter && !system->bypassCaches()) {
// let the snoop filter inspect the response and update its state
snoopFilter->updateResponse(pkt, *slavePorts[slave_port_id]);
}
// send the packet through the destination slave port and pay for
// any outstanding header delay
Tick latency = pkt->headerDelay;
pkt->headerDelay = 0;
slavePorts[slave_port_id]->schedTimingResp(pkt, curTick() + latency);
// remove the request from the routing table
routeTo.erase(route_lookup);
respLayers[slave_port_id]->succeededTiming(packetFinishTime);
// stats updates
pktCount[slave_port_id][master_port_id]++;
pktSize[slave_port_id][master_port_id] += pkt_size;
transDist[pkt_cmd]++;
return true;
}
void
CoherentXBar::recvTimingSnoopReq(PacketPtr pkt, PortID master_port_id)
{
DPRINTF(CoherentXBar, "%s: src %s packet %s\n", __func__,
masterPorts[master_port_id]->name(), pkt->print());
// update stats here as we know the forwarding will succeed
unsigned int pkt_size = pkt->hasData() ? pkt->getSize() : 0;
transDist[pkt->cmdToIndex()]++;
snoops++;
snoopTraffic += pkt_size;
// we should only see express snoops from caches
assert(pkt->isExpressSnoop());
// set the packet header and payload delay, for now use forward latency
// @todo Assess the choice of latency further
calcPacketTiming(pkt, forwardLatency * clockPeriod());
// remember if a cache has already committed to responding so we
// can see if it changes during the snooping
const bool cache_responding = pkt->cacheResponding();
assert(pkt->snoopDelay == 0);
if (snoopFilter) {
// let the Snoop Filter work its magic and guide probing
auto sf_res = snoopFilter->lookupSnoop(pkt);
// the time required by a packet to be delivered through
// the xbar has to be charged also with to lookup latency
// of the snoop filter
pkt->headerDelay += sf_res.second * clockPeriod();
DPRINTF(CoherentXBar, "%s: src %s packet %s SF size: %i lat: %i\n",
__func__, masterPorts[master_port_id]->name(), pkt->print(),
sf_res.first.size(), sf_res.second);
// forward to all snoopers
forwardTiming(pkt, InvalidPortID, sf_res.first);
} else {
forwardTiming(pkt, InvalidPortID);
}
// add the snoop delay to our header delay, and then reset it
pkt->headerDelay += pkt->snoopDelay;
pkt->snoopDelay = 0;
// if we can expect a response, remember how to route it
if (!cache_responding && pkt->cacheResponding()) {
assert(routeTo.find(pkt->req) == routeTo.end());
routeTo[pkt->req] = master_port_id;
}
// a snoop request came from a connected slave device (one of
// our master ports), and if it is not coming from the slave
// device responsible for the address range something is
// wrong, hence there is nothing further to do as the packet
// would be going back to where it came from
assert(master_port_id == findPort(pkt->getAddr()));
}
bool
CoherentXBar::recvTimingSnoopResp(PacketPtr pkt, PortID slave_port_id)
{
// determine the source port based on the id
SlavePort* src_port = slavePorts[slave_port_id];
// get the destination
const auto route_lookup = routeTo.find(pkt->req);
assert(route_lookup != routeTo.end());
const PortID dest_port_id = route_lookup->second;
assert(dest_port_id != InvalidPortID);
// determine if the response is from a snoop request we
// created as the result of a normal request (in which case it
// should be in the outstandingSnoop), or if we merely forwarded
// someone else's snoop request
const bool forwardAsSnoop = outstandingSnoop.find(pkt->req) ==
outstandingSnoop.end();
// test if the crossbar should be considered occupied for the
// current port, note that the check is bypassed if the response
// is being passed on as a normal response since this is occupying
// the response layer rather than the snoop response layer
if (forwardAsSnoop) {
assert(dest_port_id < snoopLayers.size());
if (!snoopLayers[dest_port_id]->tryTiming(src_port)) {
DPRINTF(CoherentXBar, "%s: src %s packet %s BUSY\n", __func__,
src_port->name(), pkt->print());
return false;
}
} else {
// get the master port that mirrors this slave port internally
MasterPort* snoop_port = snoopRespPorts[slave_port_id];
assert(dest_port_id < respLayers.size());
if (!respLayers[dest_port_id]->tryTiming(snoop_port)) {
DPRINTF(CoherentXBar, "%s: src %s packet %s BUSY\n", __func__,
snoop_port->name(), pkt->print());
return false;
}
}
DPRINTF(CoherentXBar, "%s: src %s packet %s\n", __func__,
src_port->name(), pkt->print());
// store size and command as they might be modified when
// forwarding the packet
unsigned int pkt_size = pkt->hasData() ? pkt->getSize() : 0;
unsigned int pkt_cmd = pkt->cmdToIndex();
// responses are never express snoops
assert(!pkt->isExpressSnoop());
// a snoop response sees the snoop response latency, and if it is
// forwarded as a normal response, the response latency
Tick xbar_delay =
(forwardAsSnoop ? snoopResponseLatency : responseLatency) *
clockPeriod();
// set the packet header and payload delay
calcPacketTiming(pkt, xbar_delay);
// determine how long to be crossbar layer is busy
Tick packetFinishTime = clockEdge(Cycles(1)) + pkt->payloadDelay;
// forward it either as a snoop response or a normal response
if (forwardAsSnoop) {
// this is a snoop response to a snoop request we forwarded,
// e.g. coming from the L1 and going to the L2, and it should
// be forwarded as a snoop response
if (snoopFilter) {
// update the probe filter so that it can properly track the line
snoopFilter->updateSnoopForward(pkt, *slavePorts[slave_port_id],
*masterPorts[dest_port_id]);
}
bool success M5_VAR_USED =
masterPorts[dest_port_id]->sendTimingSnoopResp(pkt);
pktCount[slave_port_id][dest_port_id]++;
pktSize[slave_port_id][dest_port_id] += pkt_size;
assert(success);
snoopLayers[dest_port_id]->succeededTiming(packetFinishTime);
} else {
// we got a snoop response on one of our slave ports,
// i.e. from a coherent master connected to the crossbar, and
// since we created the snoop request as part of recvTiming,
// this should now be a normal response again
outstandingSnoop.erase(pkt->req);
// this is a snoop response from a coherent master, hence it
// should never go back to where the snoop response came from,
// but instead to where the original request came from
assert(slave_port_id != dest_port_id);
if (snoopFilter) {
// update the probe filter so that it can properly track the line
snoopFilter->updateSnoopResponse(pkt, *slavePorts[slave_port_id],
*slavePorts[dest_port_id]);
}
DPRINTF(CoherentXBar, "%s: src %s packet %s FWD RESP\n", __func__,
src_port->name(), pkt->print());
// as a normal response, it should go back to a master through
// one of our slave ports, we also pay for any outstanding
// header latency
Tick latency = pkt->headerDelay;
pkt->headerDelay = 0;
slavePorts[dest_port_id]->schedTimingResp(pkt, curTick() + latency);
respLayers[dest_port_id]->succeededTiming(packetFinishTime);
}
// remove the request from the routing table
routeTo.erase(route_lookup);
// stats updates
transDist[pkt_cmd]++;
snoops++;
snoopTraffic += pkt_size;
return true;
}
void
CoherentXBar::forwardTiming(PacketPtr pkt, PortID exclude_slave_port_id,
const std::vector<QueuedSlavePort*>& dests)
{
DPRINTF(CoherentXBar, "%s for %s\n", __func__, pkt->print());
// snoops should only happen if the system isn't bypassing caches
assert(!system->bypassCaches());
unsigned fanout = 0;
for (const auto& p: dests) {
// we could have gotten this request from a snooping master
// (corresponding to our own slave port that is also in
// snoopPorts) and should not send it back to where it came
// from
if (exclude_slave_port_id == InvalidPortID ||
p->getId() != exclude_slave_port_id) {
// cache is not allowed to refuse snoop
p->sendTimingSnoopReq(pkt);
fanout++;
}
}
// Stats for fanout of this forward operation
snoopFanout.sample(fanout);
}
void
CoherentXBar::recvReqRetry(PortID master_port_id)
{
// responses and snoop responses never block on forwarding them,
// so the retry will always be coming from a port to which we
// tried to forward a request
reqLayers[master_port_id]->recvRetry();
}
Tick
CoherentXBar::recvAtomic(PacketPtr pkt, PortID slave_port_id)
{
DPRINTF(CoherentXBar, "%s: src %s packet %s\n", __func__,
slavePorts[slave_port_id]->name(), pkt->print());
unsigned int pkt_size = pkt->hasData() ? pkt->getSize() : 0;
unsigned int pkt_cmd = pkt->cmdToIndex();
MemCmd snoop_response_cmd = MemCmd::InvalidCmd;
Tick snoop_response_latency = 0;
if (!system->bypassCaches()) {
// forward to all snoopers but the source
std::pair<MemCmd, Tick> snoop_result;
if (snoopFilter) {
// check with the snoop filter where to forward this packet
auto sf_res =
snoopFilter->lookupRequest(pkt, *slavePorts[slave_port_id]);
snoop_response_latency += sf_res.second * clockPeriod();
DPRINTF(CoherentXBar, "%s: src %s packet %s SF size: %i lat: %i\n",
__func__, slavePorts[slave_port_id]->name(), pkt->print(),
sf_res.first.size(), sf_res.second);
// let the snoop filter know about the success of the send
// operation, and do it even before sending it onwards to
// avoid situations where atomic upward snoops sneak in
// between and change the filter state
snoopFilter->finishRequest(false, pkt->getAddr(), pkt->isSecure());
snoop_result = forwardAtomic(pkt, slave_port_id, InvalidPortID,
sf_res.first);
} else {
snoop_result = forwardAtomic(pkt, slave_port_id);
}
snoop_response_cmd = snoop_result.first;
snoop_response_latency += snoop_result.second;
}
// set up a sensible default value
Tick response_latency = 0;
const bool sink_packet = sinkPacket(pkt);
// even if we had a snoop response, we must continue and also
// perform the actual request at the destination
PortID master_port_id = findPort(pkt->getAddr());
if (sink_packet) {
DPRINTF(CoherentXBar, "%s: Not forwarding %s\n", __func__,
pkt->print());
} else {
if (!pointOfCoherency || pkt->isRead() || pkt->isWrite()) {
// forward the request to the appropriate destination
response_latency = masterPorts[master_port_id]->sendAtomic(pkt);
} else {
// if it does not need a response we sink the packet above
assert(pkt->needsResponse());
pkt->makeResponse();
}
}
// stats updates for the request
pktCount[slave_port_id][master_port_id]++;
pktSize[slave_port_id][master_port_id] += pkt_size;
transDist[pkt_cmd]++;
// if lower levels have replied, tell the snoop filter
if (!system->bypassCaches() && snoopFilter && pkt->isResponse()) {
snoopFilter->updateResponse(pkt, *slavePorts[slave_port_id]);
}
// if we got a response from a snooper, restore it here
if (snoop_response_cmd != MemCmd::InvalidCmd) {
// no one else should have responded
assert(!pkt->isResponse());
pkt->cmd = snoop_response_cmd;
response_latency = snoop_response_latency;
}
// add the response data
if (pkt->isResponse()) {
pkt_size = pkt->hasData() ? pkt->getSize() : 0;
pkt_cmd = pkt->cmdToIndex();
// stats updates
pktCount[slave_port_id][master_port_id]++;
pktSize[slave_port_id][master_port_id] += pkt_size;
transDist[pkt_cmd]++;
}
// @todo: Not setting header time
pkt->payloadDelay = response_latency;
return response_latency;
}
Tick
CoherentXBar::recvAtomicSnoop(PacketPtr pkt, PortID master_port_id)
{
DPRINTF(CoherentXBar, "%s: src %s packet %s\n", __func__,
masterPorts[master_port_id]->name(), pkt->print());
// add the request snoop data
unsigned int pkt_size = pkt->hasData() ? pkt->getSize() : 0;
snoops++;
snoopTraffic += pkt_size;
// forward to all snoopers
std::pair<MemCmd, Tick> snoop_result;
Tick snoop_response_latency = 0;
if (snoopFilter) {
auto sf_res = snoopFilter->lookupSnoop(pkt);
snoop_response_latency += sf_res.second * clockPeriod();
DPRINTF(CoherentXBar, "%s: src %s packet %s SF size: %i lat: %i\n",
__func__, masterPorts[master_port_id]->name(), pkt->print(),
sf_res.first.size(), sf_res.second);
snoop_result = forwardAtomic(pkt, InvalidPortID, master_port_id,
sf_res.first);
} else {
snoop_result = forwardAtomic(pkt, InvalidPortID);
}
MemCmd snoop_response_cmd = snoop_result.first;
snoop_response_latency += snoop_result.second;
if (snoop_response_cmd != MemCmd::InvalidCmd)
pkt->cmd = snoop_response_cmd;
// add the response snoop data
if (pkt->isResponse()) {
snoops++;
}
// @todo: Not setting header time
pkt->payloadDelay = snoop_response_latency;
return snoop_response_latency;
}
std::pair<MemCmd, Tick>
CoherentXBar::forwardAtomic(PacketPtr pkt, PortID exclude_slave_port_id,
PortID source_master_port_id,
const std::vector<QueuedSlavePort*>& dests)
{
// the packet may be changed on snoops, record the original
// command to enable us to restore it between snoops so that
// additional snoops can take place properly
MemCmd orig_cmd = pkt->cmd;
MemCmd snoop_response_cmd = MemCmd::InvalidCmd;
Tick snoop_response_latency = 0;
// snoops should only happen if the system isn't bypassing caches
assert(!system->bypassCaches());
unsigned fanout = 0;
for (const auto& p: dests) {
// we could have gotten this request from a snooping master
// (corresponding to our own slave port that is also in
// snoopPorts) and should not send it back to where it came
// from
if (exclude_slave_port_id != InvalidPortID &&
p->getId() == exclude_slave_port_id)
continue;
Tick latency = p->sendAtomicSnoop(pkt);
fanout++;
// in contrast to a functional access, we have to keep on
// going as all snoopers must be updated even if we get a
// response
if (!pkt->isResponse())
continue;
// response from snoop agent
assert(pkt->cmd != orig_cmd);
assert(pkt->cacheResponding());
// should only happen once
assert(snoop_response_cmd == MemCmd::InvalidCmd);
// save response state
snoop_response_cmd = pkt->cmd;
snoop_response_latency = latency;
if (snoopFilter) {
// Handle responses by the snoopers and differentiate between
// responses to requests from above and snoops from below
if (source_master_port_id != InvalidPortID) {
// Getting a response for a snoop from below
assert(exclude_slave_port_id == InvalidPortID);
snoopFilter->updateSnoopForward(pkt, *p,
*masterPorts[source_master_port_id]);
} else {
// Getting a response for a request from above
assert(source_master_port_id == InvalidPortID);
snoopFilter->updateSnoopResponse(pkt, *p,
*slavePorts[exclude_slave_port_id]);
}
}
// restore original packet state for remaining snoopers
pkt->cmd = orig_cmd;
}
// Stats for fanout
snoopFanout.sample(fanout);
// the packet is restored as part of the loop and any potential
// snoop response is part of the returned pair
return std::make_pair(snoop_response_cmd, snoop_response_latency);
}
void
CoherentXBar::recvFunctional(PacketPtr pkt, PortID slave_port_id)
{
if (!pkt->isPrint()) {
// don't do DPRINTFs on PrintReq as it clutters up the output
DPRINTF(CoherentXBar, "%s: src %s packet %s\n", __func__,
slavePorts[slave_port_id]->name(), pkt->print());
}
if (!system->bypassCaches()) {
// forward to all snoopers but the source
forwardFunctional(pkt, slave_port_id);
}
// there is no need to continue if the snooping has found what we
// were looking for and the packet is already a response
if (!pkt->isResponse()) {
// since our slave ports are queued ports we need to check them as well
for (const auto& p : slavePorts) {
// if we find a response that has the data, then the
// downstream caches/memories may be out of date, so simply stop
// here
if (p->checkFunctional(pkt)) {
if (pkt->needsResponse())
pkt->makeResponse();
return;
}
}
PortID dest_id = findPort(pkt->getAddr());
masterPorts[dest_id]->sendFunctional(pkt);
}
}
void
CoherentXBar::recvFunctionalSnoop(PacketPtr pkt, PortID master_port_id)
{
if (!pkt->isPrint()) {
// don't do DPRINTFs on PrintReq as it clutters up the output
DPRINTF(CoherentXBar, "%s: src %s packet %s\n", __func__,
masterPorts[master_port_id]->name(), pkt->print());
}
for (const auto& p : slavePorts) {
if (p->checkFunctional(pkt)) {
if (pkt->needsResponse())
pkt->makeResponse();
return;
}
}
// forward to all snoopers
forwardFunctional(pkt, InvalidPortID);
}
void
CoherentXBar::forwardFunctional(PacketPtr pkt, PortID exclude_slave_port_id)
{
// snoops should only happen if the system isn't bypassing caches
assert(!system->bypassCaches());
for (const auto& p: snoopPorts) {
// we could have gotten this request from a snooping master
// (corresponding to our own slave port that is also in
// snoopPorts) and should not send it back to where it came
// from
if (exclude_slave_port_id == InvalidPortID ||
p->getId() != exclude_slave_port_id)
p->sendFunctionalSnoop(pkt);
// if we get a response we are done
if (pkt->isResponse()) {
break;
}
}
}
bool
CoherentXBar::sinkPacket(const PacketPtr pkt) const
{
// we can sink the packet if:
// 1) the crossbar is the point of coherency, and a cache is
// responding after being snooped
// 2) the crossbar is the point of coherency, and the packet is a
// coherency packet (not a read or a write) that does not
// require a response
// 3) this is a clean evict or clean writeback, but the packet is
// found in a cache above this crossbar
// 4) a cache is responding after being snooped, and the packet
// either does not need the block to be writable, or the cache
// that has promised to respond (setting the cache responding
// flag) is providing writable and thus had a Modified block,
// and no further action is needed
return (pointOfCoherency && pkt->cacheResponding()) ||
(pointOfCoherency && !(pkt->isRead() || pkt->isWrite()) &&
!pkt->needsResponse()) ||
(pkt->isCleanEviction() && pkt->isBlockCached()) ||
(pkt->cacheResponding() &&
(!pkt->needsWritable() || pkt->responderHadWritable()));
}
void
CoherentXBar::regStats()
{
// register the stats of the base class and our layers
BaseXBar::regStats();
for (auto l: reqLayers)
l->regStats();
for (auto l: respLayers)
l->regStats();
for (auto l: snoopLayers)
l->regStats();
snoops
.name(name() + ".snoops")
.desc("Total snoops (count)")
;
snoopTraffic
.name(name() + ".snoopTraffic")
.desc("Total snoop traffic (bytes)")
;
snoopFanout
.init(0, snoopPorts.size(), 1)
.name(name() + ".snoop_fanout")
.desc("Request fanout histogram")
;
}
CoherentXBar *
CoherentXBarParams::create()
{
return new CoherentXBar(this);
}