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Diffstat (limited to 'src/mem/snoop_filter.hh')
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diff --git a/src/mem/snoop_filter.hh b/src/mem/snoop_filter.hh new file mode 100755 index 000000000..c1bb65dfc --- /dev/null +++ b/src/mem/snoop_filter.hh @@ -0,0 +1,260 @@ +/* + * Copyright (c) 2013 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. + * + * 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: Stephan Diestelhorst <stephan.diestelhorst@arm.com> + */ + +/** + * @file + * Definition of a snoop filter. + */ + +#ifndef __MEM_SNOOP_FILTER_HH__ +#define __MEM_SNOOP_FILTER_HH__ + +#include <utility> + +#include "base/hashmap.hh" +#include "mem/packet.hh" +#include "mem/port.hh" +#include "params/SnoopFilter.hh" +#include "sim/sim_object.hh" +#include "sim/system.hh" + +/** + * This snoop filter keeps track of which connected port has a + * particular line of data. It can be queried (through lookup*) on + * memory requests from above (reads / writes / ...); and also from + * below (snoops). The snoop filter precisely knows about the location + * of lines "above" it through a map from cache line address to + * sharers/ports. The snoop filter ties into the flows of requests + * (when they succeed at the lower interface), regular responses from + * below and also responses from sideway's caches (in update*). This + * allows the snoop filter to model cache-line residency by snooping + * the messages. + * + * The tracking happens in two fields to be able to distinguish + * between in-flight requests (in requested) and already pulled in + * lines (in holder). This distinction is used for producing tighter + * assertions and tracking request completion. For safety, (requested + * | holder) should be notified and the requesting MSHRs will take + * care of ordering. + * + * Overall, some trickery is required because: + * (1) snoops are not followed by an ACK, but only evoke a response if + * they need to (hit dirty) + * (2) side-channel information is funnelled through direct modifications of + * pkt, instead of proper messages through the bus + * (3) there are no clean evict messages telling the snoop filter that a local, + * upper cache dropped a line, making the snoop filter pessimistic for now + * (4) ordering: there is no single point of order in the system. Instead, + * requesting MSHRs track order between local requests and remote snoops + */ +class SnoopFilter : public SimObject { + public: + typedef std::vector<SlavePort*> SnoopList; + + SnoopFilter (const SnoopFilterParams *p) : SimObject(p), + linesize(p->system->cacheLineSize()), lookupLatency(p->lookup_latency) + { + } + + /** + * Init a new snoop filter and tell it about all the slave ports of the + * enclosing bus. + * + * @param bus_slave_ports Vector of slave ports that the bus is attached to. + */ + void setSlavePorts(const std::vector<SlavePort*>& bus_slave_ports) { + slavePorts = bus_slave_ports; + } + + /** + * Lookup a request (from a slave port) in the snoop filter and return a + * list of other slave ports that need forwarding of the resulting snoops. + * Additionally, update the tracking structures with new request + * information. + * + * @param cpkt Pointer to the request packet. Not changed. + * @param slave_port Slave port where the request came from. + * @return Pair of a vector of snoop target ports and lookup latency. + */ + std::pair<SnoopList, Cycles> lookupRequest(const Packet* cpkt, + const SlavePort& slave_port); + + /** + * For a successful request, update all data structures in the snoop filter + * reflecting the changes caused by that request + * + * @param cpkt Pointer to the request packet. Not changed. + * @param slave_port Slave port where the request came from. + * @param will_retry This request will retry on this bus / snoop filter + */ + void updateRequest(const Packet* cpkt, const SlavePort& slave_port, + bool will_retry); + + /** + * Handle an incoming snoop from below (the master port). These can upgrade the + * tracking logic and may also benefit from additional steering thanks to the + * snoop filter. + * @param cpkt Pointer to const Packet containing the snoop. + * @return Pair with a vector of SlavePorts that need snooping and a lookup + * latency. + */ + std::pair<SnoopList, Cycles> lookupSnoop(const Packet* cpkt); + + /** + * Let the snoop filter see any snoop responses that turn into request responses + * and indicate cache to cache transfers. These will update the corresponding + * state in the filter. + * + * @param cpkt Pointer to const Packet holding the snoop response. + * @param rsp_port SlavePort that sends the response. + * @param req_port SlavePort that made the original request and is the + * destination of the snoop response. + */ + void updateSnoopResponse(const Packet *cpkt, const SlavePort& rsp_port, + const SlavePort& req_port); + + /** + * Pass snoop responses that travel downward through the snoop filter and let + * them update the snoop filter state. No additional routing happens. + * + * @param cpkt Pointer to const Packet holding the snoop response. + * @param rsp_port SlavePort that sends the response. + * @param req_port MasterPort through which the response leaves this cluster. + */ + void updateSnoopForward(const Packet *cpkt, const SlavePort& rsp_port, + const MasterPort& req_port); + + /** + * Update the snoop filter with a response from below (outer / other cache, + * or memory) and update the tracking information in the snoop filter. + * + * @param cpkt Pointer to const Packet holding the snoop response. + * @param slave_port SlavePort that made the original request and is the target + * of this response. + */ + void updateResponse(const Packet *cpkt, const SlavePort& slave_port); + + /** + * Simple factory methods for standard return values for lookupRequest + */ + std::pair<SnoopList, Cycles> snoopAll(Cycles latency) const + { + return std::make_pair(slavePorts, latency); + } + std::pair<SnoopList, Cycles> snoopSelected(const SnoopList& slave_ports, + Cycles latency) const + { + return std::make_pair(slave_ports, latency); + } + std::pair<SnoopList, Cycles> snoopDown(Cycles latency) const + { + SnoopList empty; + return std::make_pair(empty , latency); + } + + protected: + typedef uint64_t SnoopMask; + /** + * Per cache line item tracking a bitmask of SlavePorts who have an + * outstanding request to this line (requested) or already share a cache line + * with this address (holder). + */ + struct SnoopItem { + SnoopMask requested; + SnoopMask holder; + }; + /** + * Convert a single port to a corresponding, one-hot bitmask + * @param port SlavePort that should be converted. + * @return One-hot bitmask corresponding to the port. + */ + SnoopMask portToMask(const SlavePort& port) const; + /** + * Convert multiple ports to a corresponding bitmask + * @param ports SnoopList that should be converted. + * @return Bitmask corresponding to the ports in the list. + */ + SnoopMask portListToMask(const SnoopList& ports) const; + /** + * Converts a bitmask of ports into the corresponing list of ports + * @param ports SnoopMask of the requested ports + * @return SnoopList containing all the requested SlavePorts + */ + SnoopList maskToPortList(SnoopMask ports) const; + + private: + /** Simple hash set of cached addresses. */ + m5::hash_map<Addr, SnoopItem> cachedLocations; + /** List of all attached slave ports. */ + SnoopList slavePorts; + /** Cache line size. */ + const unsigned linesize; + /** Latency for doing a lookup in the filter */ + const Cycles lookupLatency; +}; + +inline SnoopFilter::SnoopMask +SnoopFilter::portToMask(const SlavePort& port) const +{ + unsigned id = (unsigned)port.getId(); + assert(id != (unsigned)InvalidPortID); + assert((int)id < 8 * sizeof(SnoopMask)); + + return ((SnoopMask)1) << id; +} + +inline SnoopFilter::SnoopMask +SnoopFilter::portListToMask(const SnoopList& ports) const +{ + SnoopMask m = 0; + for (auto port = ports.begin(); port != ports.end(); ++port) + m |= portToMask(**port); + return m; +} + +inline SnoopFilter::SnoopList +SnoopFilter::maskToPortList(SnoopMask port_mask) const +{ + SnoopList res; + for (auto port = slavePorts.begin(); port != slavePorts.end(); ++port) + if (port_mask & portToMask(**port)) + res.push_back(*port); + return res; +} +#endif // __MEM_SNOOP_FILTER_HH__ |