/* * Copyright (c) 2013-2016 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. * * 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 */ /** * @file * Definition of a snoop filter. */ #ifndef __MEM_SNOOP_FILTER_HH__ #define __MEM_SNOOP_FILTER_HH__ #include #include #include "mem/packet.hh" #include "mem/port.hh" #include "mem/qport.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 SnoopList; SnoopFilter (const SnoopFilterParams *p) : SimObject(p), reqLookupResult(cachedLocations.end()), retryItem{0, 0}, linesize(p->system->cacheLineSize()), lookupLatency(p->lookup_latency), maxEntryCount(p->max_capacity / p->system->cacheLineSize()) { } /** * Init a new snoop filter and tell it about all the slave ports * of the enclosing bus. * * @param slave_ports Slave ports that the bus is attached to. */ void setSlavePorts(const SnoopList& slave_ports) { localSlavePortIds.resize(slave_ports.size(), InvalidPortID); PortID id = 0; for (const auto& p : slave_ports) { // no need to track this port if it is not snooping if (p->isSnooping()) { slavePorts.push_back(p); localSlavePortIds[p->getId()] = id++; } } // make sure we can deal with this many ports fatal_if(id > 8 * sizeof(SnoopMask), "Snoop filter only supports %d snooping ports, got %d\n", 8 * sizeof(SnoopMask), id); } /** * 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. Note that the caller must also * call finishRequest once it is known if the request needs to * retry or not. * * @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 lookupRequest(const Packet* cpkt, const SlavePort& slave_port); /** * For an un-successful request, revert the change to the snoop * filter. Also take care of erasing any null entries. This method * relies on the result from lookupRequest being stored in * reqLookupResult. * * @param will_retry This request will retry on this bus / snoop filter * @param addr Packet address, merely for sanity checking */ void finishRequest(bool will_retry, Addr addr, bool is_secure); /** * 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 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 is forwarded. */ 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); virtual void regStats(); protected: /** * The underlying type for the bitmask we use for tracking. This * limits the number of snooping ports supported per crossbar. For * the moment it is an uint64_t to offer maximum * scalability. However, it is possible to use e.g. a uint16_t or * uint32_to slim down the footprint of the hash map (and * ultimately improve the simulation performance). */ 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; }; /** * HashMap of SnoopItems indexed by line address */ typedef std::unordered_map SnoopFilterCache; /** * Simple factory methods for standard return values. */ std::pair snoopAll(Cycles latency) const { return std::make_pair(slavePorts, latency); } std::pair snoopSelected(const SnoopList& slave_ports, Cycles latency) const { return std::make_pair(slave_ports, latency); } std::pair snoopDown(Cycles latency) const { SnoopList empty; return std::make_pair(empty , latency); } /** * 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; /** * 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: /** * Removes snoop filter items which have no requesters and no holders. */ void eraseIfNullEntry(SnoopFilterCache::iterator& sf_it); /** Simple hash set of cached addresses. */ SnoopFilterCache cachedLocations; /** * Iterator used to store the result from lookupRequest until we * call finishRequest. */ SnoopFilterCache::iterator reqLookupResult; /** * Variable to temporarily store value of snoopfilter entry * incase finishRequest needs to undo changes made in lookupRequest * (because of crossbar retry) */ SnoopItem retryItem; /** List of all attached snooping slave ports. */ SnoopList slavePorts; /** Track the mapping from port ids to the local mask ids. */ std::vector localSlavePortIds; /** Cache line size. */ const unsigned linesize; /** Latency for doing a lookup in the filter */ const Cycles lookupLatency; /** Max capacity in terms of cache blocks tracked, for sanity checking */ const unsigned maxEntryCount; /** * Use the lower bits of the address to keep track of the line status */ enum LineStatus { /** block holds data from the secure memory space */ LineSecure = 0x01, }; /** Statistics */ Stats::Scalar totRequests; Stats::Scalar hitSingleRequests; Stats::Scalar hitMultiRequests; Stats::Scalar totSnoops; Stats::Scalar hitSingleSnoops; Stats::Scalar hitMultiSnoops; }; inline SnoopFilter::SnoopMask SnoopFilter::portToMask(const SlavePort& port) const { assert(port.getId() != InvalidPortID); // if this is not a snooping port, return a zero mask return !port.isSnooping() ? 0 : ((SnoopMask)1) << localSlavePortIds[port.getId()]; } inline SnoopFilter::SnoopList SnoopFilter::maskToPortList(SnoopMask port_mask) const { SnoopList res; for (const auto& p : slavePorts) if (port_mask & portToMask(*p)) res.push_back(p); return res; } #endif // __MEM_SNOOP_FILTER_HH__