snoop_filter.hh revision 11135
1/* 2 * Copyright (c) 2013-2015 ARM Limited 3 * All rights reserved 4 * 5 * The license below extends only to copyright in the software and shall 6 * not be construed as granting a license to any other intellectual 7 * property including but not limited to intellectual property relating 8 * to a hardware implementation of the functionality of the software 9 * licensed hereunder. You may use the software subject to the license 10 * terms below provided that you ensure that this notice is replicated 11 * unmodified and in its entirety in all distributions of the software, 12 * modified or unmodified, in source code or in binary form. 13 * 14 * Redistribution and use in source and binary forms, with or without 15 * modification, are permitted provided that the following conditions are 16 * met: redistributions of source code must retain the above copyright 17 * notice, this list of conditions and the following disclaimer; 18 * redistributions in binary form must reproduce the above copyright 19 * notice, this list of conditions and the following disclaimer in the 20 * documentation and/or other materials provided with the distribution; 21 * neither the name of the copyright holders nor the names of its 22 * contributors may be used to endorse or promote products derived from 23 * this software without specific prior written permission. 24 * 25 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS 26 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT 27 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR 28 * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT 29 * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, 30 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT 31 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, 32 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY 33 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT 34 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE 35 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 36 * 37 * Authors: Stephan Diestelhorst 38 */ 39 40/** 41 * @file 42 * Definition of a snoop filter. 43 */ 44 45#ifndef __MEM_SNOOP_FILTER_HH__ 46#define __MEM_SNOOP_FILTER_HH__ 47 48#include <utility> 49 50#include "base/hashmap.hh" 51#include "mem/packet.hh" 52#include "mem/port.hh" 53#include "mem/qport.hh" 54#include "params/SnoopFilter.hh" 55#include "sim/sim_object.hh" 56#include "sim/system.hh" 57 58/** 59 * This snoop filter keeps track of which connected port has a 60 * particular line of data. It can be queried (through lookup*) on 61 * memory requests from above (reads / writes / ...); and also from 62 * below (snoops). The snoop filter precisely knows about the location 63 * of lines "above" it through a map from cache line address to 64 * sharers/ports. The snoop filter ties into the flows of requests 65 * (when they succeed at the lower interface), regular responses from 66 * below and also responses from sideway's caches (in update*). This 67 * allows the snoop filter to model cache-line residency by snooping 68 * the messages. 69 * 70 * The tracking happens in two fields to be able to distinguish 71 * between in-flight requests (in requested) and already pulled in 72 * lines (in holder). This distinction is used for producing tighter 73 * assertions and tracking request completion. For safety, (requested 74 * | holder) should be notified and the requesting MSHRs will take 75 * care of ordering. 76 * 77 * Overall, some trickery is required because: 78 * (1) snoops are not followed by an ACK, but only evoke a response if 79 * they need to (hit dirty) 80 * (2) side-channel information is funnelled through direct modifications of 81 * pkt, instead of proper messages through the bus 82 * (3) there are no clean evict messages telling the snoop filter that a local, 83 * upper cache dropped a line, making the snoop filter pessimistic for now 84 * (4) ordering: there is no single point of order in the system. Instead, 85 * requesting MSHRs track order between local requests and remote snoops 86 */ 87class SnoopFilter : public SimObject { 88 public: 89 typedef std::vector<QueuedSlavePort*> SnoopList; 90 91 SnoopFilter (const SnoopFilterParams *p) : 92 SimObject(p), reqLookupResult(cachedLocations.end()), retryItem{0, 0}, 93 linesize(p->system->cacheLineSize()), lookupLatency(p->lookup_latency), 94 maxEntryCount(p->max_capacity / p->system->cacheLineSize()) 95 { 96 } 97 98 /** 99 * Init a new snoop filter and tell it about all the slave ports 100 * of the enclosing bus. 101 * 102 * @param slave_ports Slave ports that the bus is attached to. 103 */ 104 void setSlavePorts(const SnoopList& slave_ports) { 105 localSlavePortIds.resize(slave_ports.size(), InvalidPortID); 106 107 PortID id = 0; 108 for (const auto& p : slave_ports) { 109 // no need to track this port if it is not snooping 110 if (p->isSnooping()) { 111 slavePorts.push_back(p); 112 localSlavePortIds[p->getId()] = id++; 113 } 114 } 115 116 // make sure we can deal with this many ports 117 fatal_if(id > 8 * sizeof(SnoopMask), 118 "Snoop filter only supports %d snooping ports, got %d\n", 119 8 * sizeof(SnoopMask), id); 120 } 121 122 /** 123 * Lookup a request (from a slave port) in the snoop filter and 124 * return a list of other slave ports that need forwarding of the 125 * resulting snoops. Additionally, update the tracking structures 126 * with new request information. Note that the caller must also 127 * call finishRequest once it is known if the request needs to 128 * retry or not. 129 * 130 * @param cpkt Pointer to the request packet. Not changed. 131 * @param slave_port Slave port where the request came from. 132 * @return Pair of a vector of snoop target ports and lookup latency. 133 */ 134 std::pair<SnoopList, Cycles> lookupRequest(const Packet* cpkt, 135 const SlavePort& slave_port); 136 137 /** 138 * For an un-successful request, revert the change to the snoop 139 * filter. Also take care of erasing any null entries. This method 140 * relies on the result from lookupRequest being stored in 141 * reqLookupResult. 142 * 143 * @param will_retry This request will retry on this bus / snoop filter 144 * @param cpkt Request packet, merely for sanity checking 145 */ 146 void finishRequest(bool will_retry, const Packet* cpkt); 147 148 /** 149 * Handle an incoming snoop from below (the master port). These 150 * can upgrade the tracking logic and may also benefit from 151 * additional steering thanks to the snoop filter. 152 * 153 * @param cpkt Pointer to const Packet containing the snoop. 154 * @return Pair with a vector of SlavePorts that need snooping and a lookup 155 * latency. 156 */ 157 std::pair<SnoopList, Cycles> lookupSnoop(const Packet* cpkt); 158 159 /** 160 * Let the snoop filter see any snoop responses that turn into 161 * request responses and indicate cache to cache transfers. These 162 * will update the corresponding state in the filter. 163 * 164 * @param cpkt Pointer to const Packet holding the snoop response. 165 * @param rsp_port SlavePort that sends the response. 166 * @param req_port SlavePort that made the original request and is the 167 * destination of the snoop response. 168 */ 169 void updateSnoopResponse(const Packet *cpkt, const SlavePort& rsp_port, 170 const SlavePort& req_port); 171 172 /** 173 * Pass snoop responses that travel downward through the snoop 174 * filter and let them update the snoop filter state. No 175 * additional routing happens. 176 * 177 * @param cpkt Pointer to const Packet holding the snoop response. 178 * @param rsp_port SlavePort that sends the response. 179 * @param req_port MasterPort through which the response is forwarded. 180 */ 181 void updateSnoopForward(const Packet *cpkt, const SlavePort& rsp_port, 182 const MasterPort& req_port); 183 184 /** 185 * Update the snoop filter with a response from below (outer / 186 * other cache, or memory) and update the tracking information in 187 * the snoop filter. 188 * 189 * @param cpkt Pointer to const Packet holding the snoop response. 190 * @param slave_port SlavePort that made the original request and 191 * is the target of this response. 192 */ 193 void updateResponse(const Packet *cpkt, const SlavePort& slave_port); 194 195 virtual void regStats(); 196 197 protected: 198 199 /** 200 * The underlying type for the bitmask we use for tracking. This 201 * limits the number of snooping ports supported per crossbar. For 202 * the moment it is an uint64_t to offer maximum 203 * scalability. However, it is possible to use e.g. a uint16_t or 204 * uint32_to slim down the footprint of the hash map (and 205 * ultimately improve the simulation performance). 206 */ 207 typedef uint64_t SnoopMask; 208 209 /** 210 * Per cache line item tracking a bitmask of SlavePorts who have an 211 * outstanding request to this line (requested) or already share a 212 * cache line with this address (holder). 213 */ 214 struct SnoopItem { 215 SnoopMask requested; 216 SnoopMask holder; 217 }; 218 /** 219 * HashMap of SnoopItems indexed by line address 220 */ 221 typedef m5::hash_map<Addr, SnoopItem> SnoopFilterCache; 222 223 /** 224 * Simple factory methods for standard return values. 225 */ 226 std::pair<SnoopList, Cycles> snoopAll(Cycles latency) const 227 { 228 return std::make_pair(slavePorts, latency); 229 } 230 std::pair<SnoopList, Cycles> snoopSelected(const SnoopList& slave_ports, 231 Cycles latency) const 232 { 233 return std::make_pair(slave_ports, latency); 234 } 235 std::pair<SnoopList, Cycles> snoopDown(Cycles latency) const 236 { 237 SnoopList empty; 238 return std::make_pair(empty , latency); 239 } 240 241 /** 242 * Convert a single port to a corresponding, one-hot bitmask 243 * @param port SlavePort that should be converted. 244 * @return One-hot bitmask corresponding to the port. 245 */ 246 SnoopMask portToMask(const SlavePort& port) const; 247 /** 248 * Converts a bitmask of ports into the corresponing list of ports 249 * @param ports SnoopMask of the requested ports 250 * @return SnoopList containing all the requested SlavePorts 251 */ 252 SnoopList maskToPortList(SnoopMask ports) const; 253 254 private: 255 256 /** 257 * Removes snoop filter items which have no requesters and no holders. 258 */ 259 void eraseIfNullEntry(SnoopFilterCache::iterator& sf_it); 260 261 /** Simple hash set of cached addresses. */ 262 SnoopFilterCache cachedLocations; 263 /** 264 * Iterator used to store the result from lookupRequest until we 265 * call finishRequest. 266 */ 267 SnoopFilterCache::iterator reqLookupResult; 268 /** 269 * Variable to temporarily store value of snoopfilter entry 270 * incase finishRequest needs to undo changes made in lookupRequest 271 * (because of crossbar retry) 272 */ 273 SnoopItem retryItem; 274 /** List of all attached snooping slave ports. */ 275 SnoopList slavePorts; 276 /** Track the mapping from port ids to the local mask ids. */ 277 std::vector<PortID> localSlavePortIds; 278 /** Cache line size. */ 279 const unsigned linesize; 280 /** Latency for doing a lookup in the filter */ 281 const Cycles lookupLatency; 282 /** Max capacity in terms of cache blocks tracked, for sanity checking */ 283 const unsigned maxEntryCount; 284 285 /** Statistics */ 286 Stats::Scalar totRequests; 287 Stats::Scalar hitSingleRequests; 288 Stats::Scalar hitMultiRequests; 289 290 Stats::Scalar totSnoops; 291 Stats::Scalar hitSingleSnoops; 292 Stats::Scalar hitMultiSnoops; 293}; 294 295inline SnoopFilter::SnoopMask 296SnoopFilter::portToMask(const SlavePort& port) const 297{ 298 assert(port.getId() != InvalidPortID); 299 // if this is not a snooping port, return a zero mask 300 return !port.isSnooping() ? 0 : 301 ((SnoopMask)1) << localSlavePortIds[port.getId()]; 302} 303 304inline SnoopFilter::SnoopList 305SnoopFilter::maskToPortList(SnoopMask port_mask) const 306{ 307 SnoopList res; 308 for (const auto& p : slavePorts) 309 if (port_mask & portToMask(*p)) 310 res.push_back(p); 311 return res; 312} 313 314#endif // __MEM_SNOOP_FILTER_HH__ 315