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48 * Definition of a crossbar object.
51 #include "mem/coherent_xbar.hh"
53 #include "base/logging.hh"
54 #include "base/trace.hh"
55 #include "debug/AddrRanges.hh"
56 #include "debug/CoherentXBar.hh"
57 #include "sim/system.hh"
59 CoherentXBar::CoherentXBar(const CoherentXBarParams
*p
)
60 : BaseXBar(p
), system(p
->system
), snoopFilter(p
->snoop_filter
),
61 snoopResponseLatency(p
->snoop_response_latency
),
62 pointOfCoherency(p
->point_of_coherency
),
63 pointOfUnification(p
->point_of_unification
)
65 // create the ports based on the size of the master and slave
66 // vector ports, and the presence of the default port, the ports
67 // are enumerated starting from zero
68 for (int i
= 0; i
< p
->port_master_connection_count
; ++i
) {
69 std::string portName
= csprintf("%s.master[%d]", name(), i
);
70 MasterPort
* bp
= new CoherentXBarMasterPort(portName
, *this, i
);
71 masterPorts
.push_back(bp
);
72 reqLayers
.push_back(new ReqLayer(*bp
, *this,
73 csprintf(".reqLayer%d", i
)));
74 snoopLayers
.push_back(new SnoopRespLayer(*bp
, *this,
75 csprintf(".snoopLayer%d", i
)));
78 // see if we have a default slave device connected and if so add
79 // our corresponding master port
80 if (p
->port_default_connection_count
) {
81 defaultPortID
= masterPorts
.size();
82 std::string portName
= name() + ".default";
83 MasterPort
* bp
= new CoherentXBarMasterPort(portName
, *this,
85 masterPorts
.push_back(bp
);
86 reqLayers
.push_back(new ReqLayer(*bp
, *this, csprintf(".reqLayer%d",
88 snoopLayers
.push_back(new SnoopRespLayer(*bp
, *this,
89 csprintf(".snoopLayer%d",
93 // create the slave ports, once again starting at zero
94 for (int i
= 0; i
< p
->port_slave_connection_count
; ++i
) {
95 std::string portName
= csprintf("%s.slave[%d]", name(), i
);
96 QueuedSlavePort
* bp
= new CoherentXBarSlavePort(portName
, *this, i
);
97 slavePorts
.push_back(bp
);
98 respLayers
.push_back(new RespLayer(*bp
, *this,
99 csprintf(".respLayer%d", i
)));
100 snoopRespPorts
.push_back(new SnoopRespPort(*bp
, *this));
104 CoherentXBar::~CoherentXBar()
106 for (auto l
: reqLayers
)
108 for (auto l
: respLayers
)
110 for (auto l
: snoopLayers
)
112 for (auto p
: snoopRespPorts
)
121 // iterate over our slave ports and determine which of our
122 // neighbouring master ports are snooping and add them as snoopers
123 for (const auto& p
: slavePorts
) {
124 // check if the connected master port is snooping
125 if (p
->isSnooping()) {
126 DPRINTF(AddrRanges
, "Adding snooping master %s\n",
127 p
->getMasterPort().name());
128 snoopPorts
.push_back(p
);
132 if (snoopPorts
.empty())
133 warn("CoherentXBar %s has no snooping ports attached!\n", name());
135 // inform the snoop filter about the slave ports so it can create
136 // its own internal representation
138 snoopFilter
->setSlavePorts(slavePorts
);
142 CoherentXBar::recvTimingReq(PacketPtr pkt
, PortID slave_port_id
)
144 // determine the source port based on the id
145 SlavePort
*src_port
= slavePorts
[slave_port_id
];
147 // remember if the packet is an express snoop
148 bool is_express_snoop
= pkt
->isExpressSnoop();
149 bool cache_responding
= pkt
->cacheResponding();
150 // for normal requests, going downstream, the express snoop flag
151 // and the cache responding flag should always be the same
152 assert(is_express_snoop
== cache_responding
);
154 // determine the destination based on the destination address range
155 AddrRange addr_range
= RangeSize(pkt
->getAddr(), pkt
->getSize());
156 PortID master_port_id
= findPort(addr_range
);
158 // test if the crossbar should be considered occupied for the current
159 // port, and exclude express snoops from the check
160 if (!is_express_snoop
&& !reqLayers
[master_port_id
]->tryTiming(src_port
)) {
161 DPRINTF(CoherentXBar
, "%s: src %s packet %s BUSY\n", __func__
,
162 src_port
->name(), pkt
->print());
166 DPRINTF(CoherentXBar
, "%s: src %s packet %s\n", __func__
,
167 src_port
->name(), pkt
->print());
169 // store size and command as they might be modified when
170 // forwarding the packet
171 unsigned int pkt_size
= pkt
->hasData() ? pkt
->getSize() : 0;
172 unsigned int pkt_cmd
= pkt
->cmdToIndex();
174 // store the old header delay so we can restore it if needed
175 Tick old_header_delay
= pkt
->headerDelay
;
177 // a request sees the frontend and forward latency
178 Tick xbar_delay
= (frontendLatency
+ forwardLatency
) * clockPeriod();
180 // set the packet header and payload delay
181 calcPacketTiming(pkt
, xbar_delay
);
183 // determine how long to be crossbar layer is busy
184 Tick packetFinishTime
= clockEdge(Cycles(1)) + pkt
->payloadDelay
;
186 // is this the destination point for this packet? (e.g. true if
187 // this xbar is the PoC for a cache maintenance operation to the
188 // PoC) otherwise the destination is any cache that can satisfy
190 const bool is_destination
= isDestination(pkt
);
192 const bool snoop_caches
= !system
->bypassCaches() &&
193 pkt
->cmd
!= MemCmd::WriteClean
;
195 assert(pkt
->snoopDelay
== 0);
197 if (pkt
->isClean() && !is_destination
) {
198 // before snooping we need to make sure that the memory
199 // below is not busy and the cache clean request can be
201 if (!masterPorts
[master_port_id
]->tryTiming(pkt
)) {
202 DPRINTF(CoherentXBar
, "%s: src %s packet %s RETRY\n", __func__
,
203 src_port
->name(), pkt
->print());
205 // update the layer state and schedule an idle event
206 reqLayers
[master_port_id
]->failedTiming(src_port
,
207 clockEdge(Cycles(1)));
213 // the packet is a memory-mapped request and should be
214 // broadcasted to our snoopers but the source
216 // check with the snoop filter where to forward this packet
217 auto sf_res
= snoopFilter
->lookupRequest(pkt
, *src_port
);
218 // the time required by a packet to be delivered through
219 // the xbar has to be charged also with to lookup latency
220 // of the snoop filter
221 pkt
->headerDelay
+= sf_res
.second
* clockPeriod();
222 DPRINTF(CoherentXBar
, "%s: src %s packet %s SF size: %i lat: %i\n",
223 __func__
, src_port
->name(), pkt
->print(),
224 sf_res
.first
.size(), sf_res
.second
);
226 if (pkt
->isEviction()) {
227 // for block-evicting packets, i.e. writebacks and
228 // clean evictions, there is no need to snoop up, as
229 // all we do is determine if the block is cached or
230 // not, instead just set it here based on the snoop
232 if (!sf_res
.first
.empty())
233 pkt
->setBlockCached();
235 forwardTiming(pkt
, slave_port_id
, sf_res
.first
);
238 forwardTiming(pkt
, slave_port_id
);
241 // add the snoop delay to our header delay, and then reset it
242 pkt
->headerDelay
+= pkt
->snoopDelay
;
246 // set up a sensible starting point
249 // remember if the packet will generate a snoop response by
250 // checking if a cache set the cacheResponding flag during the
252 const bool expect_snoop_resp
= !cache_responding
&& pkt
->cacheResponding();
253 bool expect_response
= pkt
->needsResponse() && !pkt
->cacheResponding();
255 const bool sink_packet
= sinkPacket(pkt
);
257 // in certain cases the crossbar is responsible for responding
258 bool respond_directly
= false;
259 // store the original address as an address mapper could possibly
260 // modify the address upon a sendTimingRequest
261 const Addr
addr(pkt
->getAddr());
263 DPRINTF(CoherentXBar
, "%s: Not forwarding %s\n", __func__
,
266 // determine if we are forwarding the packet, or responding to
268 if (forwardPacket(pkt
)) {
269 // if we are passing on, rather than sinking, a packet to
270 // which an upstream cache has committed to responding,
271 // the line was needs writable, and the responding only
272 // had an Owned copy, so we need to immidiately let the
273 // downstream caches know, bypass any flow control
274 if (pkt
->cacheResponding()) {
275 pkt
->setExpressSnoop();
278 // make sure that the write request (e.g., WriteClean)
279 // will stop at the memory below if this crossbar is its
281 if (pkt
->isWrite() && is_destination
) {
282 pkt
->clearWriteThrough();
285 // since it is a normal request, attempt to send the packet
286 success
= masterPorts
[master_port_id
]->sendTimingReq(pkt
);
288 // no need to forward, turn this packet around and respond
290 assert(pkt
->needsResponse());
292 respond_directly
= true;
293 assert(!expect_snoop_resp
);
294 expect_response
= false;
298 if (snoopFilter
&& snoop_caches
) {
299 // Let the snoop filter know about the success of the send operation
300 snoopFilter
->finishRequest(!success
, addr
, pkt
->isSecure());
303 // check if we were successful in sending the packet onwards
305 // express snoops should never be forced to retry
306 assert(!is_express_snoop
);
308 // restore the header delay
309 pkt
->headerDelay
= old_header_delay
;
311 DPRINTF(CoherentXBar
, "%s: src %s packet %s RETRY\n", __func__
,
312 src_port
->name(), pkt
->print());
314 // update the layer state and schedule an idle event
315 reqLayers
[master_port_id
]->failedTiming(src_port
,
316 clockEdge(Cycles(1)));
318 // express snoops currently bypass the crossbar state entirely
319 if (!is_express_snoop
) {
320 // if this particular request will generate a snoop
322 if (expect_snoop_resp
) {
323 // we should never have an exsiting request outstanding
324 assert(outstandingSnoop
.find(pkt
->req
) ==
325 outstandingSnoop
.end());
326 outstandingSnoop
.insert(pkt
->req
);
328 // basic sanity check on the outstanding snoops
329 panic_if(outstandingSnoop
.size() > 512,
330 "Outstanding snoop requests exceeded 512\n");
333 // remember where to route the normal response to
334 if (expect_response
|| expect_snoop_resp
) {
335 assert(routeTo
.find(pkt
->req
) == routeTo
.end());
336 routeTo
[pkt
->req
] = slave_port_id
;
338 panic_if(routeTo
.size() > 512,
339 "Routing table exceeds 512 packets\n");
342 // update the layer state and schedule an idle event
343 reqLayers
[master_port_id
]->succeededTiming(packetFinishTime
);
346 // stats updates only consider packets that were successfully sent
347 pktCount
[slave_port_id
][master_port_id
]++;
348 pktSize
[slave_port_id
][master_port_id
] += pkt_size
;
349 transDist
[pkt_cmd
]++;
351 if (is_express_snoop
) {
353 snoopTraffic
+= pkt_size
;
358 // queue the packet for deletion
359 pendingDelete
.reset(pkt
);
361 // normally we respond to the packet we just received if we need to
362 PacketPtr rsp_pkt
= pkt
;
363 PortID rsp_port_id
= slave_port_id
;
365 // If this is the destination of the cache clean operation the
366 // crossbar is responsible for responding. This crossbar will
367 // respond when the cache clean is complete. A cache clean
368 // is complete either:
369 // * direcly, if no cache above had a dirty copy of the block
370 // as indicated by the satisfied flag of the packet, or
371 // * when the crossbar has seen both the cache clean request
372 // (CleanSharedReq, CleanInvalidReq) and the corresponding
373 // write (WriteClean) which updates the block in the memory
376 ((pkt
->isClean() && pkt
->satisfied()) ||
377 pkt
->cmd
== MemCmd::WriteClean
) &&
379 PacketPtr deferred_rsp
= pkt
->isWrite() ? nullptr : pkt
;
380 auto cmo_lookup
= outstandingCMO
.find(pkt
->id
);
381 if (cmo_lookup
!= outstandingCMO
.end()) {
382 // the cache clean request has already reached this xbar
383 respond_directly
= true;
384 if (pkt
->isWrite()) {
385 rsp_pkt
= cmo_lookup
->second
;
388 // determine the destination
389 const auto route_lookup
= routeTo
.find(rsp_pkt
->req
);
390 assert(route_lookup
!= routeTo
.end());
391 rsp_port_id
= route_lookup
->second
;
392 assert(rsp_port_id
!= InvalidPortID
);
393 assert(rsp_port_id
< respLayers
.size());
394 // remove the request from the routing table
395 routeTo
.erase(route_lookup
);
397 outstandingCMO
.erase(cmo_lookup
);
399 respond_directly
= false;
400 outstandingCMO
.emplace(pkt
->id
, deferred_rsp
);
401 if (!pkt
->isWrite()) {
402 assert(routeTo
.find(pkt
->req
) == routeTo
.end());
403 routeTo
[pkt
->req
] = slave_port_id
;
405 panic_if(routeTo
.size() > 512,
406 "Routing table exceeds 512 packets\n");
412 if (respond_directly
) {
413 assert(rsp_pkt
->needsResponse());
416 rsp_pkt
->makeResponse();
418 if (snoopFilter
&& !system
->bypassCaches()) {
419 // let the snoop filter inspect the response and update its state
420 snoopFilter
->updateResponse(rsp_pkt
, *slavePorts
[rsp_port_id
]);
423 // we send the response after the current packet, even if the
424 // response is not for this packet (e.g. cache clean operation
425 // where both the request and the write packet have to cross
426 // the destination xbar before the response is sent.)
427 Tick response_time
= clockEdge() + pkt
->headerDelay
;
428 rsp_pkt
->headerDelay
= 0;
430 slavePorts
[rsp_port_id
]->schedTimingResp(rsp_pkt
, response_time
);
437 CoherentXBar::recvTimingResp(PacketPtr pkt
, PortID master_port_id
)
439 // determine the source port based on the id
440 MasterPort
*src_port
= masterPorts
[master_port_id
];
442 // determine the destination
443 const auto route_lookup
= routeTo
.find(pkt
->req
);
444 assert(route_lookup
!= routeTo
.end());
445 const PortID slave_port_id
= route_lookup
->second
;
446 assert(slave_port_id
!= InvalidPortID
);
447 assert(slave_port_id
< respLayers
.size());
449 // test if the crossbar should be considered occupied for the
451 if (!respLayers
[slave_port_id
]->tryTiming(src_port
)) {
452 DPRINTF(CoherentXBar
, "%s: src %s packet %s BUSY\n", __func__
,
453 src_port
->name(), pkt
->print());
457 DPRINTF(CoherentXBar
, "%s: src %s packet %s\n", __func__
,
458 src_port
->name(), pkt
->print());
460 // store size and command as they might be modified when
461 // forwarding the packet
462 unsigned int pkt_size
= pkt
->hasData() ? pkt
->getSize() : 0;
463 unsigned int pkt_cmd
= pkt
->cmdToIndex();
465 // a response sees the response latency
466 Tick xbar_delay
= responseLatency
* clockPeriod();
468 // set the packet header and payload delay
469 calcPacketTiming(pkt
, xbar_delay
);
471 // determine how long to be crossbar layer is busy
472 Tick packetFinishTime
= clockEdge(Cycles(1)) + pkt
->payloadDelay
;
474 if (snoopFilter
&& !system
->bypassCaches()) {
475 // let the snoop filter inspect the response and update its state
476 snoopFilter
->updateResponse(pkt
, *slavePorts
[slave_port_id
]);
479 // send the packet through the destination slave port and pay for
480 // any outstanding header delay
481 Tick latency
= pkt
->headerDelay
;
482 pkt
->headerDelay
= 0;
483 slavePorts
[slave_port_id
]->schedTimingResp(pkt
, curTick() + latency
);
485 // remove the request from the routing table
486 routeTo
.erase(route_lookup
);
488 respLayers
[slave_port_id
]->succeededTiming(packetFinishTime
);
491 pktCount
[slave_port_id
][master_port_id
]++;
492 pktSize
[slave_port_id
][master_port_id
] += pkt_size
;
493 transDist
[pkt_cmd
]++;
499 CoherentXBar::recvTimingSnoopReq(PacketPtr pkt
, PortID master_port_id
)
501 DPRINTF(CoherentXBar
, "%s: src %s packet %s\n", __func__
,
502 masterPorts
[master_port_id
]->name(), pkt
->print());
504 // update stats here as we know the forwarding will succeed
505 unsigned int pkt_size
= pkt
->hasData() ? pkt
->getSize() : 0;
506 transDist
[pkt
->cmdToIndex()]++;
508 snoopTraffic
+= pkt_size
;
510 // we should only see express snoops from caches
511 assert(pkt
->isExpressSnoop());
513 // set the packet header and payload delay, for now use forward latency
514 // @todo Assess the choice of latency further
515 calcPacketTiming(pkt
, forwardLatency
* clockPeriod());
517 // remember if a cache has already committed to responding so we
518 // can see if it changes during the snooping
519 const bool cache_responding
= pkt
->cacheResponding();
521 assert(pkt
->snoopDelay
== 0);
524 // let the Snoop Filter work its magic and guide probing
525 auto sf_res
= snoopFilter
->lookupSnoop(pkt
);
526 // the time required by a packet to be delivered through
527 // the xbar has to be charged also with to lookup latency
528 // of the snoop filter
529 pkt
->headerDelay
+= sf_res
.second
* clockPeriod();
530 DPRINTF(CoherentXBar
, "%s: src %s packet %s SF size: %i lat: %i\n",
531 __func__
, masterPorts
[master_port_id
]->name(), pkt
->print(),
532 sf_res
.first
.size(), sf_res
.second
);
534 // forward to all snoopers
535 forwardTiming(pkt
, InvalidPortID
, sf_res
.first
);
537 forwardTiming(pkt
, InvalidPortID
);
540 // add the snoop delay to our header delay, and then reset it
541 pkt
->headerDelay
+= pkt
->snoopDelay
;
544 // if we can expect a response, remember how to route it
545 if (!cache_responding
&& pkt
->cacheResponding()) {
546 assert(routeTo
.find(pkt
->req
) == routeTo
.end());
547 routeTo
[pkt
->req
] = master_port_id
;
550 // a snoop request came from a connected slave device (one of
551 // our master ports), and if it is not coming from the slave
552 // device responsible for the address range something is
553 // wrong, hence there is nothing further to do as the packet
554 // would be going back to where it came from
555 AddrRange addr_range M5_VAR_USED
=
556 RangeSize(pkt
->getAddr(), pkt
->getSize());
557 assert(findPort(addr_range
) == master_port_id
);
561 CoherentXBar::recvTimingSnoopResp(PacketPtr pkt
, PortID slave_port_id
)
563 // determine the source port based on the id
564 SlavePort
* src_port
= slavePorts
[slave_port_id
];
566 // get the destination
567 const auto route_lookup
= routeTo
.find(pkt
->req
);
568 assert(route_lookup
!= routeTo
.end());
569 const PortID dest_port_id
= route_lookup
->second
;
570 assert(dest_port_id
!= InvalidPortID
);
572 // determine if the response is from a snoop request we
573 // created as the result of a normal request (in which case it
574 // should be in the outstandingSnoop), or if we merely forwarded
575 // someone else's snoop request
576 const bool forwardAsSnoop
= outstandingSnoop
.find(pkt
->req
) ==
577 outstandingSnoop
.end();
579 // test if the crossbar should be considered occupied for the
580 // current port, note that the check is bypassed if the response
581 // is being passed on as a normal response since this is occupying
582 // the response layer rather than the snoop response layer
583 if (forwardAsSnoop
) {
584 assert(dest_port_id
< snoopLayers
.size());
585 if (!snoopLayers
[dest_port_id
]->tryTiming(src_port
)) {
586 DPRINTF(CoherentXBar
, "%s: src %s packet %s BUSY\n", __func__
,
587 src_port
->name(), pkt
->print());
591 // get the master port that mirrors this slave port internally
592 MasterPort
* snoop_port
= snoopRespPorts
[slave_port_id
];
593 assert(dest_port_id
< respLayers
.size());
594 if (!respLayers
[dest_port_id
]->tryTiming(snoop_port
)) {
595 DPRINTF(CoherentXBar
, "%s: src %s packet %s BUSY\n", __func__
,
596 snoop_port
->name(), pkt
->print());
601 DPRINTF(CoherentXBar
, "%s: src %s packet %s\n", __func__
,
602 src_port
->name(), pkt
->print());
604 // store size and command as they might be modified when
605 // forwarding the packet
606 unsigned int pkt_size
= pkt
->hasData() ? pkt
->getSize() : 0;
607 unsigned int pkt_cmd
= pkt
->cmdToIndex();
609 // responses are never express snoops
610 assert(!pkt
->isExpressSnoop());
612 // a snoop response sees the snoop response latency, and if it is
613 // forwarded as a normal response, the response latency
615 (forwardAsSnoop
? snoopResponseLatency
: responseLatency
) *
618 // set the packet header and payload delay
619 calcPacketTiming(pkt
, xbar_delay
);
621 // determine how long to be crossbar layer is busy
622 Tick packetFinishTime
= clockEdge(Cycles(1)) + pkt
->payloadDelay
;
624 // forward it either as a snoop response or a normal response
625 if (forwardAsSnoop
) {
626 // this is a snoop response to a snoop request we forwarded,
627 // e.g. coming from the L1 and going to the L2, and it should
628 // be forwarded as a snoop response
631 // update the probe filter so that it can properly track the line
632 snoopFilter
->updateSnoopForward(pkt
, *slavePorts
[slave_port_id
],
633 *masterPorts
[dest_port_id
]);
636 bool success M5_VAR_USED
=
637 masterPorts
[dest_port_id
]->sendTimingSnoopResp(pkt
);
638 pktCount
[slave_port_id
][dest_port_id
]++;
639 pktSize
[slave_port_id
][dest_port_id
] += pkt_size
;
642 snoopLayers
[dest_port_id
]->succeededTiming(packetFinishTime
);
644 // we got a snoop response on one of our slave ports,
645 // i.e. from a coherent master connected to the crossbar, and
646 // since we created the snoop request as part of recvTiming,
647 // this should now be a normal response again
648 outstandingSnoop
.erase(pkt
->req
);
650 // this is a snoop response from a coherent master, hence it
651 // should never go back to where the snoop response came from,
652 // but instead to where the original request came from
653 assert(slave_port_id
!= dest_port_id
);
656 // update the probe filter so that it can properly track the line
657 snoopFilter
->updateSnoopResponse(pkt
, *slavePorts
[slave_port_id
],
658 *slavePorts
[dest_port_id
]);
661 DPRINTF(CoherentXBar
, "%s: src %s packet %s FWD RESP\n", __func__
,
662 src_port
->name(), pkt
->print());
664 // as a normal response, it should go back to a master through
665 // one of our slave ports, we also pay for any outstanding
667 Tick latency
= pkt
->headerDelay
;
668 pkt
->headerDelay
= 0;
669 slavePorts
[dest_port_id
]->schedTimingResp(pkt
, curTick() + latency
);
671 respLayers
[dest_port_id
]->succeededTiming(packetFinishTime
);
674 // remove the request from the routing table
675 routeTo
.erase(route_lookup
);
678 transDist
[pkt_cmd
]++;
680 snoopTraffic
+= pkt_size
;
687 CoherentXBar::forwardTiming(PacketPtr pkt
, PortID exclude_slave_port_id
,
688 const std::vector
<QueuedSlavePort
*>& dests
)
690 DPRINTF(CoherentXBar
, "%s for %s\n", __func__
, pkt
->print());
692 // snoops should only happen if the system isn't bypassing caches
693 assert(!system
->bypassCaches());
697 for (const auto& p
: dests
) {
698 // we could have gotten this request from a snooping master
699 // (corresponding to our own slave port that is also in
700 // snoopPorts) and should not send it back to where it came
702 if (exclude_slave_port_id
== InvalidPortID
||
703 p
->getId() != exclude_slave_port_id
) {
704 // cache is not allowed to refuse snoop
705 p
->sendTimingSnoopReq(pkt
);
710 // Stats for fanout of this forward operation
711 snoopFanout
.sample(fanout
);
715 CoherentXBar::recvReqRetry(PortID master_port_id
)
717 // responses and snoop responses never block on forwarding them,
718 // so the retry will always be coming from a port to which we
719 // tried to forward a request
720 reqLayers
[master_port_id
]->recvRetry();
724 CoherentXBar::recvAtomic(PacketPtr pkt
, PortID slave_port_id
)
726 DPRINTF(CoherentXBar
, "%s: src %s packet %s\n", __func__
,
727 slavePorts
[slave_port_id
]->name(), pkt
->print());
729 unsigned int pkt_size
= pkt
->hasData() ? pkt
->getSize() : 0;
730 unsigned int pkt_cmd
= pkt
->cmdToIndex();
732 MemCmd snoop_response_cmd
= MemCmd::InvalidCmd
;
733 Tick snoop_response_latency
= 0;
735 // is this the destination point for this packet? (e.g. true if
736 // this xbar is the PoC for a cache maintenance operation to the
737 // PoC) otherwise the destination is any cache that can satisfy
739 const bool is_destination
= isDestination(pkt
);
741 const bool snoop_caches
= !system
->bypassCaches() &&
742 pkt
->cmd
!= MemCmd::WriteClean
;
744 // forward to all snoopers but the source
745 std::pair
<MemCmd
, Tick
> snoop_result
;
747 // check with the snoop filter where to forward this packet
749 snoopFilter
->lookupRequest(pkt
, *slavePorts
[slave_port_id
]);
750 snoop_response_latency
+= sf_res
.second
* clockPeriod();
751 DPRINTF(CoherentXBar
, "%s: src %s packet %s SF size: %i lat: %i\n",
752 __func__
, slavePorts
[slave_port_id
]->name(), pkt
->print(),
753 sf_res
.first
.size(), sf_res
.second
);
755 // let the snoop filter know about the success of the send
756 // operation, and do it even before sending it onwards to
757 // avoid situations where atomic upward snoops sneak in
758 // between and change the filter state
759 snoopFilter
->finishRequest(false, pkt
->getAddr(), pkt
->isSecure());
761 if (pkt
->isEviction()) {
762 // for block-evicting packets, i.e. writebacks and
763 // clean evictions, there is no need to snoop up, as
764 // all we do is determine if the block is cached or
765 // not, instead just set it here based on the snoop
767 if (!sf_res
.first
.empty())
768 pkt
->setBlockCached();
770 snoop_result
= forwardAtomic(pkt
, slave_port_id
, InvalidPortID
,
774 snoop_result
= forwardAtomic(pkt
, slave_port_id
);
776 snoop_response_cmd
= snoop_result
.first
;
777 snoop_response_latency
+= snoop_result
.second
;
780 // set up a sensible default value
781 Tick response_latency
= 0;
783 const bool sink_packet
= sinkPacket(pkt
);
785 // even if we had a snoop response, we must continue and also
786 // perform the actual request at the destination
787 AddrRange addr_range
= RangeSize(pkt
->getAddr(), pkt
->getSize());
788 PortID master_port_id
= findPort(addr_range
);
791 DPRINTF(CoherentXBar
, "%s: Not forwarding %s\n", __func__
,
794 if (forwardPacket(pkt
)) {
795 // make sure that the write request (e.g., WriteClean)
796 // will stop at the memory below if this crossbar is its
798 if (pkt
->isWrite() && is_destination
) {
799 pkt
->clearWriteThrough();
802 // forward the request to the appropriate destination
803 response_latency
= masterPorts
[master_port_id
]->sendAtomic(pkt
);
805 // if it does not need a response we sink the packet above
806 assert(pkt
->needsResponse());
812 // stats updates for the request
813 pktCount
[slave_port_id
][master_port_id
]++;
814 pktSize
[slave_port_id
][master_port_id
] += pkt_size
;
815 transDist
[pkt_cmd
]++;
818 // if lower levels have replied, tell the snoop filter
819 if (!system
->bypassCaches() && snoopFilter
&& pkt
->isResponse()) {
820 snoopFilter
->updateResponse(pkt
, *slavePorts
[slave_port_id
]);
823 // if we got a response from a snooper, restore it here
824 if (snoop_response_cmd
!= MemCmd::InvalidCmd
) {
825 // no one else should have responded
826 assert(!pkt
->isResponse());
827 pkt
->cmd
= snoop_response_cmd
;
828 response_latency
= snoop_response_latency
;
831 // If this is the destination of the cache clean operation the
832 // crossbar is responsible for responding. This crossbar will
833 // respond when the cache clean is complete. An atomic cache clean
834 // is complete when the crossbars receives the cache clean
835 // request (CleanSharedReq, CleanInvalidReq), as either:
836 // * no cache above had a dirty copy of the block as indicated by
837 // the satisfied flag of the packet, or
838 // * the crossbar has already seen the corresponding write
839 // (WriteClean) which updates the block in the memory below.
840 if (pkt
->isClean() && isDestination(pkt
) && pkt
->satisfied()) {
841 auto it
= outstandingCMO
.find(pkt
->id
);
842 assert(it
!= outstandingCMO
.end());
843 // we are responding right away
844 outstandingCMO
.erase(it
);
845 } else if (pkt
->cmd
== MemCmd::WriteClean
&& isDestination(pkt
)) {
846 // if this is the destination of the operation, the xbar
847 // sends the responce to the cache clean operation only
848 // after having encountered the cache clean request
849 auto M5_VAR_USED ret
= outstandingCMO
.emplace(pkt
->id
, nullptr);
850 // in atomic mode we know that the WriteClean packet should
851 // precede the clean request
855 // add the response data
856 if (pkt
->isResponse()) {
857 pkt_size
= pkt
->hasData() ? pkt
->getSize() : 0;
858 pkt_cmd
= pkt
->cmdToIndex();
861 pktCount
[slave_port_id
][master_port_id
]++;
862 pktSize
[slave_port_id
][master_port_id
] += pkt_size
;
863 transDist
[pkt_cmd
]++;
866 // @todo: Not setting header time
867 pkt
->payloadDelay
= response_latency
;
868 return response_latency
;
872 CoherentXBar::recvAtomicSnoop(PacketPtr pkt
, PortID master_port_id
)
874 DPRINTF(CoherentXBar
, "%s: src %s packet %s\n", __func__
,
875 masterPorts
[master_port_id
]->name(), pkt
->print());
877 // add the request snoop data
878 unsigned int pkt_size
= pkt
->hasData() ? pkt
->getSize() : 0;
880 snoopTraffic
+= pkt_size
;
882 // forward to all snoopers
883 std::pair
<MemCmd
, Tick
> snoop_result
;
884 Tick snoop_response_latency
= 0;
886 auto sf_res
= snoopFilter
->lookupSnoop(pkt
);
887 snoop_response_latency
+= sf_res
.second
* clockPeriod();
888 DPRINTF(CoherentXBar
, "%s: src %s packet %s SF size: %i lat: %i\n",
889 __func__
, masterPorts
[master_port_id
]->name(), pkt
->print(),
890 sf_res
.first
.size(), sf_res
.second
);
891 snoop_result
= forwardAtomic(pkt
, InvalidPortID
, master_port_id
,
894 snoop_result
= forwardAtomic(pkt
, InvalidPortID
);
896 MemCmd snoop_response_cmd
= snoop_result
.first
;
897 snoop_response_latency
+= snoop_result
.second
;
899 if (snoop_response_cmd
!= MemCmd::InvalidCmd
)
900 pkt
->cmd
= snoop_response_cmd
;
902 // add the response snoop data
903 if (pkt
->isResponse()) {
907 // @todo: Not setting header time
908 pkt
->payloadDelay
= snoop_response_latency
;
909 return snoop_response_latency
;
912 std::pair
<MemCmd
, Tick
>
913 CoherentXBar::forwardAtomic(PacketPtr pkt
, PortID exclude_slave_port_id
,
914 PortID source_master_port_id
,
915 const std::vector
<QueuedSlavePort
*>& dests
)
917 // the packet may be changed on snoops, record the original
918 // command to enable us to restore it between snoops so that
919 // additional snoops can take place properly
920 MemCmd orig_cmd
= pkt
->cmd
;
921 MemCmd snoop_response_cmd
= MemCmd::InvalidCmd
;
922 Tick snoop_response_latency
= 0;
924 // snoops should only happen if the system isn't bypassing caches
925 assert(!system
->bypassCaches());
929 for (const auto& p
: dests
) {
930 // we could have gotten this request from a snooping master
931 // (corresponding to our own slave port that is also in
932 // snoopPorts) and should not send it back to where it came
934 if (exclude_slave_port_id
!= InvalidPortID
&&
935 p
->getId() == exclude_slave_port_id
)
938 Tick latency
= p
->sendAtomicSnoop(pkt
);
941 // in contrast to a functional access, we have to keep on
942 // going as all snoopers must be updated even if we get a
944 if (!pkt
->isResponse())
947 // response from snoop agent
948 assert(pkt
->cmd
!= orig_cmd
);
949 assert(pkt
->cacheResponding());
950 // should only happen once
951 assert(snoop_response_cmd
== MemCmd::InvalidCmd
);
952 // save response state
953 snoop_response_cmd
= pkt
->cmd
;
954 snoop_response_latency
= latency
;
957 // Handle responses by the snoopers and differentiate between
958 // responses to requests from above and snoops from below
959 if (source_master_port_id
!= InvalidPortID
) {
960 // Getting a response for a snoop from below
961 assert(exclude_slave_port_id
== InvalidPortID
);
962 snoopFilter
->updateSnoopForward(pkt
, *p
,
963 *masterPorts
[source_master_port_id
]);
965 // Getting a response for a request from above
966 assert(source_master_port_id
== InvalidPortID
);
967 snoopFilter
->updateSnoopResponse(pkt
, *p
,
968 *slavePorts
[exclude_slave_port_id
]);
971 // restore original packet state for remaining snoopers
976 snoopFanout
.sample(fanout
);
978 // the packet is restored as part of the loop and any potential
979 // snoop response is part of the returned pair
980 return std::make_pair(snoop_response_cmd
, snoop_response_latency
);
984 CoherentXBar::recvFunctional(PacketPtr pkt
, PortID slave_port_id
)
986 if (!pkt
->isPrint()) {
987 // don't do DPRINTFs on PrintReq as it clutters up the output
988 DPRINTF(CoherentXBar
, "%s: src %s packet %s\n", __func__
,
989 slavePorts
[slave_port_id
]->name(), pkt
->print());
992 if (!system
->bypassCaches()) {
993 // forward to all snoopers but the source
994 forwardFunctional(pkt
, slave_port_id
);
997 // there is no need to continue if the snooping has found what we
998 // were looking for and the packet is already a response
999 if (!pkt
->isResponse()) {
1000 // since our slave ports are queued ports we need to check them as well
1001 for (const auto& p
: slavePorts
) {
1002 // if we find a response that has the data, then the
1003 // downstream caches/memories may be out of date, so simply stop
1005 if (p
->checkFunctional(pkt
)) {
1006 if (pkt
->needsResponse())
1007 pkt
->makeResponse();
1012 PortID dest_id
= findPort(RangeSize(pkt
->getAddr(), pkt
->getSize()));
1014 masterPorts
[dest_id
]->sendFunctional(pkt
);
1019 CoherentXBar::recvFunctionalSnoop(PacketPtr pkt
, PortID master_port_id
)
1021 if (!pkt
->isPrint()) {
1022 // don't do DPRINTFs on PrintReq as it clutters up the output
1023 DPRINTF(CoherentXBar
, "%s: src %s packet %s\n", __func__
,
1024 masterPorts
[master_port_id
]->name(), pkt
->print());
1027 for (const auto& p
: slavePorts
) {
1028 if (p
->checkFunctional(pkt
)) {
1029 if (pkt
->needsResponse())
1030 pkt
->makeResponse();
1035 // forward to all snoopers
1036 forwardFunctional(pkt
, InvalidPortID
);
1040 CoherentXBar::forwardFunctional(PacketPtr pkt
, PortID exclude_slave_port_id
)
1042 // snoops should only happen if the system isn't bypassing caches
1043 assert(!system
->bypassCaches());
1045 for (const auto& p
: snoopPorts
) {
1046 // we could have gotten this request from a snooping master
1047 // (corresponding to our own slave port that is also in
1048 // snoopPorts) and should not send it back to where it came
1050 if (exclude_slave_port_id
== InvalidPortID
||
1051 p
->getId() != exclude_slave_port_id
)
1052 p
->sendFunctionalSnoop(pkt
);
1054 // if we get a response we are done
1055 if (pkt
->isResponse()) {
1062 CoherentXBar::sinkPacket(const PacketPtr pkt
) const
1064 // we can sink the packet if:
1065 // 1) the crossbar is the point of coherency, and a cache is
1066 // responding after being snooped
1067 // 2) the crossbar is the point of coherency, and the packet is a
1068 // coherency packet (not a read or a write) that does not
1069 // require a response
1070 // 3) this is a clean evict or clean writeback, but the packet is
1071 // found in a cache above this crossbar
1072 // 4) a cache is responding after being snooped, and the packet
1073 // either does not need the block to be writable, or the cache
1074 // that has promised to respond (setting the cache responding
1075 // flag) is providing writable and thus had a Modified block,
1076 // and no further action is needed
1077 return (pointOfCoherency
&& pkt
->cacheResponding()) ||
1078 (pointOfCoherency
&& !(pkt
->isRead() || pkt
->isWrite()) &&
1079 !pkt
->needsResponse()) ||
1080 (pkt
->isCleanEviction() && pkt
->isBlockCached()) ||
1081 (pkt
->cacheResponding() &&
1082 (!pkt
->needsWritable() || pkt
->responderHadWritable()));
1086 CoherentXBar::forwardPacket(const PacketPtr pkt
)
1088 // we are forwarding the packet if:
1089 // 1) this is a cache clean request to the PoU/PoC and this
1090 // crossbar is above the PoU/PoC
1091 // 2) this is a read or a write
1092 // 3) this crossbar is above the point of coherency
1093 if (pkt
->isClean()) {
1094 return !isDestination(pkt
);
1096 return pkt
->isRead() || pkt
->isWrite() || !pointOfCoherency
;
1101 CoherentXBar::regStats()
1103 // register the stats of the base class and our layers
1104 BaseXBar::regStats();
1105 for (auto l
: reqLayers
)
1107 for (auto l
: respLayers
)
1109 for (auto l
: snoopLayers
)
1113 .name(name() + ".snoops")
1114 .desc("Total snoops (count)")
1118 .name(name() + ".snoopTraffic")
1119 .desc("Total snoop traffic (bytes)")
1123 .init(0, snoopPorts
.size(), 1)
1124 .name(name() + ".snoop_fanout")
1125 .desc("Request fanout histogram")
1130 CoherentXBarParams::create()
1132 return new CoherentXBar(this);