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40 * Authors: Ron Dreslinski
48 * Declaration of a coherent crossbar.
51 #ifndef __MEM_COHERENT_XBAR_HH__
52 #define __MEM_COHERENT_XBAR_HH__
54 #include <unordered_map>
55 #include <unordered_set>
57 #include "mem/snoop_filter.hh"
58 #include "mem/xbar.hh"
59 #include "params/CoherentXBar.hh"
62 * A coherent crossbar connects a number of (potentially) snooping
63 * masters and slaves, and routes the request and response packets
64 * based on the address, and also forwards all requests to the
65 * snoopers and deals with the snoop responses.
67 * The coherent crossbar can be used as a template for modelling QPI,
68 * HyperTransport, ACE and coherent OCP buses, and is typically used
69 * for the L1-to-L2 buses and as the main system interconnect. @sa
70 * \ref gem5MemorySystem "gem5 Memory System"
72 class CoherentXBar : public BaseXBar
78 * Declare the layers of this crossbar, one vector for requests,
79 * one for responses, and one for snoop responses
81 std::vector<ReqLayer*> reqLayers;
82 std::vector<RespLayer*> respLayers;
83 std::vector<SnoopRespLayer*> snoopLayers;
86 * Declaration of the coherent crossbar slave port type, one will
87 * be instantiated for each of the master ports connecting to the
90 class CoherentXBarSlavePort : public QueuedSlavePort
95 /** A reference to the crossbar to which this port belongs. */
98 /** A normal packet queue used to store responses. */
99 RespPacketQueue queue;
103 CoherentXBarSlavePort(const std::string &_name,
104 CoherentXBar &_xbar, PortID _id)
105 : QueuedSlavePort(_name, &_xbar, queue, _id), xbar(_xbar),
112 * When receiving a timing request, pass it to the crossbar.
114 virtual bool recvTimingReq(PacketPtr pkt)
115 { return xbar.recvTimingReq(pkt, id); }
118 * When receiving a timing snoop response, pass it to the crossbar.
120 virtual bool recvTimingSnoopResp(PacketPtr pkt)
121 { return xbar.recvTimingSnoopResp(pkt, id); }
124 * When receiving an atomic request, pass it to the crossbar.
126 virtual Tick recvAtomic(PacketPtr pkt)
127 { return xbar.recvAtomic(pkt, id); }
130 * When receiving a functional request, pass it to the crossbar.
132 virtual void recvFunctional(PacketPtr pkt)
133 { xbar.recvFunctional(pkt, id); }
136 * Return the union of all adress ranges seen by this crossbar.
138 virtual AddrRangeList getAddrRanges() const
139 { return xbar.getAddrRanges(); }
144 * Declaration of the coherent crossbar master port type, one will be
145 * instantiated for each of the slave interfaces connecting to the
148 class CoherentXBarMasterPort : public MasterPort
151 /** A reference to the crossbar to which this port belongs. */
156 CoherentXBarMasterPort(const std::string &_name,
157 CoherentXBar &_xbar, PortID _id)
158 : MasterPort(_name, &_xbar, _id), xbar(_xbar)
164 * Determine if this port should be considered a snooper. For
165 * a coherent crossbar master port this is always true.
167 * @return a boolean that is true if this port is snooping
169 virtual bool isSnooping() const
173 * When receiving a timing response, pass it to the crossbar.
175 virtual bool recvTimingResp(PacketPtr pkt)
176 { return xbar.recvTimingResp(pkt, id); }
179 * When receiving a timing snoop request, pass it to the crossbar.
181 virtual void recvTimingSnoopReq(PacketPtr pkt)
182 { return xbar.recvTimingSnoopReq(pkt, id); }
185 * When receiving an atomic snoop request, pass it to the crossbar.
187 virtual Tick recvAtomicSnoop(PacketPtr pkt)
188 { return xbar.recvAtomicSnoop(pkt, id); }
191 * When receiving a functional snoop request, pass it to the crossbar.
193 virtual void recvFunctionalSnoop(PacketPtr pkt)
194 { xbar.recvFunctionalSnoop(pkt, id); }
196 /** When reciving a range change from the peer port (at id),
197 pass it to the crossbar. */
198 virtual void recvRangeChange()
199 { xbar.recvRangeChange(id); }
201 /** When reciving a retry from the peer port (at id),
202 pass it to the crossbar. */
203 virtual void recvReqRetry()
204 { xbar.recvReqRetry(id); }
209 * Internal class to bridge between an incoming snoop response
210 * from a slave port and forwarding it through an outgoing slave
211 * port. It is effectively a dangling master port.
213 class SnoopRespPort : public MasterPort
218 /** The port which we mirror internally. */
219 QueuedSlavePort& slavePort;
224 * Create a snoop response port that mirrors a given slave port.
226 SnoopRespPort(QueuedSlavePort& slave_port, CoherentXBar& _xbar) :
227 MasterPort(slave_port.name() + ".snoopRespPort", &_xbar),
228 slavePort(slave_port) { }
231 * Override the sending of retries and pass them on through
232 * the mirrored slave port.
234 void sendRetryResp() {
235 // forward it as a snoop response retry
236 slavePort.sendRetrySnoopResp();
240 * Provided as necessary.
242 void recvReqRetry() { panic("SnoopRespPort should never see retry\n"); }
245 * Provided as necessary.
247 bool recvTimingResp(PacketPtr pkt)
249 panic("SnoopRespPort should never see timing response\n");
255 std::vector<SnoopRespPort*> snoopRespPorts;
257 std::vector<QueuedSlavePort*> snoopPorts;
260 * Store the outstanding requests that we are expecting snoop
261 * responses from so we can determine which snoop responses we
262 * generated and which ones were merely forwarded.
264 std::unordered_set<RequestPtr> outstandingSnoop;
267 * Store the outstanding cache maintenance that we are expecting
268 * snoop responses from so we can determine when we received all
269 * snoop responses and if any of the agents satisfied the request.
271 std::unordered_map<PacketId, PacketPtr> outstandingCMO;
274 * Keep a pointer to the system to be allow to querying memory system
279 /** A snoop filter that tracks cache line residency and can restrict the
280 * broadcast needed for probes. NULL denotes an absent filter. */
281 SnoopFilter *snoopFilter;
283 /** Cycles of snoop response latency.*/
284 const Cycles snoopResponseLatency;
286 /** Is this crossbar the point of coherency? **/
287 const bool pointOfCoherency;
289 /** Is this crossbar the point of unification? **/
290 const bool pointOfUnification;
293 * Upstream caches need this packet until true is returned, so
294 * hold it for deletion until a subsequent call
296 std::unique_ptr<Packet> pendingDelete;
298 /** Function called by the port when the crossbar is recieving a Timing
300 bool recvTimingReq(PacketPtr pkt, PortID slave_port_id);
302 /** Function called by the port when the crossbar is recieving a Timing
304 bool recvTimingResp(PacketPtr pkt, PortID master_port_id);
306 /** Function called by the port when the crossbar is recieving a timing
308 void recvTimingSnoopReq(PacketPtr pkt, PortID master_port_id);
310 /** Function called by the port when the crossbar is recieving a timing
312 bool recvTimingSnoopResp(PacketPtr pkt, PortID slave_port_id);
314 /** Timing function called by port when it is once again able to process
316 void recvReqRetry(PortID master_port_id);
319 * Forward a timing packet to our snoopers, potentially excluding
320 * one of the connected coherent masters to avoid sending a packet
321 * back to where it came from.
323 * @param pkt Packet to forward
324 * @param exclude_slave_port_id Id of slave port to exclude
326 void forwardTiming(PacketPtr pkt, PortID exclude_slave_port_id) {
327 forwardTiming(pkt, exclude_slave_port_id, snoopPorts);
331 * Forward a timing packet to a selected list of snoopers, potentially
332 * excluding one of the connected coherent masters to avoid sending a packet
333 * back to where it came from.
335 * @param pkt Packet to forward
336 * @param exclude_slave_port_id Id of slave port to exclude
337 * @param dests Vector of destination ports for the forwarded pkt
339 void forwardTiming(PacketPtr pkt, PortID exclude_slave_port_id,
340 const std::vector<QueuedSlavePort*>& dests);
342 /** Function called by the port when the crossbar is recieving a Atomic
344 Tick recvAtomic(PacketPtr pkt, PortID slave_port_id);
346 /** Function called by the port when the crossbar is recieving an
347 atomic snoop transaction.*/
348 Tick recvAtomicSnoop(PacketPtr pkt, PortID master_port_id);
351 * Forward an atomic packet to our snoopers, potentially excluding
352 * one of the connected coherent masters to avoid sending a packet
353 * back to where it came from.
355 * @param pkt Packet to forward
356 * @param exclude_slave_port_id Id of slave port to exclude
358 * @return a pair containing the snoop response and snoop latency
360 std::pair<MemCmd, Tick> forwardAtomic(PacketPtr pkt,
361 PortID exclude_slave_port_id)
363 return forwardAtomic(pkt, exclude_slave_port_id, InvalidPortID,
368 * Forward an atomic packet to a selected list of snoopers, potentially
369 * excluding one of the connected coherent masters to avoid sending a packet
370 * back to where it came from.
372 * @param pkt Packet to forward
373 * @param exclude_slave_port_id Id of slave port to exclude
374 * @param source_master_port_id Id of the master port for snoops from below
375 * @param dests Vector of destination ports for the forwarded pkt
377 * @return a pair containing the snoop response and snoop latency
379 std::pair<MemCmd, Tick> forwardAtomic(PacketPtr pkt,
380 PortID exclude_slave_port_id,
381 PortID source_master_port_id,
382 const std::vector<QueuedSlavePort*>&
385 /** Function called by the port when the crossbar is recieving a Functional
387 void recvFunctional(PacketPtr pkt, PortID slave_port_id);
389 /** Function called by the port when the crossbar is recieving a functional
391 void recvFunctionalSnoop(PacketPtr pkt, PortID master_port_id);
394 * Forward a functional packet to our snoopers, potentially
395 * excluding one of the connected coherent masters to avoid
396 * sending a packet back to where it came from.
398 * @param pkt Packet to forward
399 * @param exclude_slave_port_id Id of slave port to exclude
401 void forwardFunctional(PacketPtr pkt, PortID exclude_slave_port_id);
404 * Determine if the crossbar should sink the packet, as opposed to
405 * forwarding it, or responding.
407 bool sinkPacket(const PacketPtr pkt) const;
410 * Determine if the crossbar should forward the packet, as opposed to
413 bool forwardPacket(const PacketPtr pkt);
416 * Determine if the packet's destination is the memory below
418 * The memory below is the destination for a cache mainteance
419 * operation to the Point of Coherence/Unification if this is the
420 * Point of Coherence/Unification.
422 * @param pkt The processed packet
424 * @return Whether the memory below is the destination for the packet
426 bool isDestination(const PacketPtr pkt) const
428 return (pkt->req->isToPOC() && pointOfCoherency) ||
429 (pkt->req->isToPOU() && pointOfUnification);
432 Stats::Scalar snoops;
433 Stats::Scalar snoopTraffic;
434 Stats::Distribution snoopFanout;
440 CoherentXBar(const CoherentXBarParams *p);
442 virtual ~CoherentXBar();
444 virtual void regStats();
447 #endif //__MEM_COHERENT_XBAR_HH__