fetch.hh revision 3949:b6664282d899
1/* 2 * Copyright (c) 2004-2006 The Regents of The University of Michigan 3 * All rights reserved. 4 * 5 * Redistribution and use in source and binary forms, with or without 6 * modification, are permitted provided that the following conditions are 7 * met: redistributions of source code must retain the above copyright 8 * notice, this list of conditions and the following disclaimer; 9 * redistributions in binary form must reproduce the above copyright 10 * notice, this list of conditions and the following disclaimer in the 11 * documentation and/or other materials provided with the distribution; 12 * neither the name of the copyright holders nor the names of its 13 * contributors may be used to endorse or promote products derived from 14 * this software without specific prior written permission. 15 * 16 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS 17 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT 18 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR 19 * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT 20 * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, 21 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT 22 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, 23 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY 24 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT 25 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE 26 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 27 * 28 * Authors: Kevin Lim 29 * Korey Sewell 30 */ 31 32#ifndef __CPU_O3_FETCH_HH__ 33#define __CPU_O3_FETCH_HH__ 34 35#include "arch/utility.hh" 36#include "base/statistics.hh" 37#include "base/timebuf.hh" 38#include "cpu/pc_event.hh" 39#include "mem/packet.hh" 40#include "mem/port.hh" 41#include "sim/eventq.hh" 42 43/** 44 * DefaultFetch class handles both single threaded and SMT fetch. Its 45 * width is specified by the parameters; each cycle it tries to fetch 46 * that many instructions. It supports using a branch predictor to 47 * predict direction and targets. 48 * It supports the idling functionality of the CPU by indicating to 49 * the CPU when it is active and inactive. 50 */ 51template <class Impl> 52class DefaultFetch 53{ 54 public: 55 /** Typedefs from Impl. */ 56 typedef typename Impl::CPUPol CPUPol; 57 typedef typename Impl::DynInst DynInst; 58 typedef typename Impl::DynInstPtr DynInstPtr; 59 typedef typename Impl::O3CPU O3CPU; 60 typedef typename Impl::Params Params; 61 62 /** Typedefs from the CPU policy. */ 63 typedef typename CPUPol::BPredUnit BPredUnit; 64 typedef typename CPUPol::FetchStruct FetchStruct; 65 typedef typename CPUPol::TimeStruct TimeStruct; 66 67 /** Typedefs from ISA. */ 68 typedef TheISA::MachInst MachInst; 69 typedef TheISA::ExtMachInst ExtMachInst; 70 71 /** IcachePort class for DefaultFetch. Handles doing the 72 * communication with the cache/memory. 73 */ 74 class IcachePort : public Port 75 { 76 protected: 77 /** Pointer to fetch. */ 78 DefaultFetch<Impl> *fetch; 79 80 public: 81 /** Default constructor. */ 82 IcachePort(DefaultFetch<Impl> *_fetch) 83 : Port(_fetch->name() + "-iport"), fetch(_fetch) 84 { } 85 86 bool snoopRangeSent; 87 88 protected: 89 /** Atomic version of receive. Panics. */ 90 virtual Tick recvAtomic(PacketPtr pkt); 91 92 /** Functional version of receive. Panics. */ 93 virtual void recvFunctional(PacketPtr pkt); 94 95 /** Receives status change. Other than range changing, panics. */ 96 virtual void recvStatusChange(Status status); 97 98 /** Returns the address ranges of this device. */ 99 virtual void getDeviceAddressRanges(AddrRangeList &resp, 100 AddrRangeList &snoop) 101 { resp.clear(); snoop.clear(); snoop.push_back(RangeSize(0,0)); } 102 103 /** Timing version of receive. Handles setting fetch to the 104 * proper status to start fetching. */ 105 virtual bool recvTiming(PacketPtr pkt); 106 107 /** Handles doing a retry of a failed fetch. */ 108 virtual void recvRetry(); 109 }; 110 111 112 public: 113 /** Overall fetch status. Used to determine if the CPU can 114 * deschedule itsef due to a lack of activity. 115 */ 116 enum FetchStatus { 117 Active, 118 Inactive 119 }; 120 121 /** Individual thread status. */ 122 enum ThreadStatus { 123 Running, 124 Idle, 125 Squashing, 126 Blocked, 127 Fetching, 128 TrapPending, 129 QuiescePending, 130 SwitchOut, 131 IcacheWaitResponse, 132 IcacheWaitRetry, 133 IcacheAccessComplete 134 }; 135 136 /** Fetching Policy, Add new policies here.*/ 137 enum FetchPriority { 138 SingleThread, 139 RoundRobin, 140 Branch, 141 IQ, 142 LSQ 143 }; 144 145 private: 146 /** Fetch status. */ 147 FetchStatus _status; 148 149 /** Per-thread status. */ 150 ThreadStatus fetchStatus[Impl::MaxThreads]; 151 152 /** Fetch policy. */ 153 FetchPriority fetchPolicy; 154 155 /** List that has the threads organized by priority. */ 156 std::list<unsigned> priorityList; 157 158 public: 159 /** DefaultFetch constructor. */ 160 DefaultFetch(Params *params); 161 162 /** Returns the name of fetch. */ 163 std::string name() const; 164 165 /** Registers statistics. */ 166 void regStats(); 167 168 /** Returns the icache port. */ 169 Port *getIcachePort() { return icachePort; } 170 171 /** Sets CPU pointer. */ 172 void setCPU(O3CPU *cpu_ptr); 173 174 /** Sets the main backwards communication time buffer pointer. */ 175 void setTimeBuffer(TimeBuffer<TimeStruct> *time_buffer); 176 177 /** Sets pointer to list of active threads. */ 178 void setActiveThreads(std::list<unsigned> *at_ptr); 179 180 /** Sets pointer to time buffer used to communicate to the next stage. */ 181 void setFetchQueue(TimeBuffer<FetchStruct> *fq_ptr); 182 183 /** Initialize stage. */ 184 void initStage(); 185 186 /** Processes cache completion event. */ 187 void processCacheCompletion(PacketPtr pkt); 188 189 /** Begins the drain of the fetch stage. */ 190 bool drain(); 191 192 /** Resumes execution after a drain. */ 193 void resume(); 194 195 /** Tells fetch stage to prepare to be switched out. */ 196 void switchOut(); 197 198 /** Takes over from another CPU's thread. */ 199 void takeOverFrom(); 200 201 /** Checks if the fetch stage is switched out. */ 202 bool isSwitchedOut() { return switchedOut; } 203 204 /** Tells fetch to wake up from a quiesce instruction. */ 205 void wakeFromQuiesce(); 206 207 private: 208 /** Changes the status of this stage to active, and indicates this 209 * to the CPU. 210 */ 211 inline void switchToActive(); 212 213 /** Changes the status of this stage to inactive, and indicates 214 * this to the CPU. 215 */ 216 inline void switchToInactive(); 217 218 /** 219 * Looks up in the branch predictor to see if the next PC should be 220 * either next PC+=MachInst or a branch target. 221 * @param next_PC Next PC variable passed in by reference. It is 222 * expected to be set to the current PC; it will be updated with what 223 * the next PC will be. 224 * @param next_NPC Used for ISAs which use delay slots. 225 * @return Whether or not a branch was predicted as taken. 226 */ 227 bool lookupAndUpdateNextPC(DynInstPtr &inst, Addr &next_PC, Addr &next_NPC); 228 229 /** 230 * Fetches the cache line that contains fetch_PC. Returns any 231 * fault that happened. Puts the data into the class variable 232 * cacheData. 233 * @param fetch_PC The PC address that is being fetched from. 234 * @param ret_fault The fault reference that will be set to the result of 235 * the icache access. 236 * @param tid Thread id. 237 * @return Any fault that occured. 238 */ 239 bool fetchCacheLine(Addr fetch_PC, Fault &ret_fault, unsigned tid); 240 241 /** Squashes a specific thread and resets the PC. */ 242 inline void doSquash(const Addr &new_PC, const Addr &new_NPC, unsigned tid); 243 244 /** Squashes a specific thread and resets the PC. Also tells the CPU to 245 * remove any instructions between fetch and decode that should be sqaushed. 246 */ 247 void squashFromDecode(const Addr &new_PC, const Addr &new_NPC, 248 const InstSeqNum &seq_num, unsigned tid); 249 250 /** Checks if a thread is stalled. */ 251 bool checkStall(unsigned tid) const; 252 253 /** Updates overall fetch stage status; to be called at the end of each 254 * cycle. */ 255 FetchStatus updateFetchStatus(); 256 257 public: 258 /** Squashes a specific thread and resets the PC. Also tells the CPU to 259 * remove any instructions that are not in the ROB. The source of this 260 * squash should be the commit stage. 261 */ 262 void squash(const Addr &new_PC, const Addr &new_NPC, 263 const InstSeqNum &seq_num, 264 bool squash_delay_slot, unsigned tid); 265 266 /** Ticks the fetch stage, processing all inputs signals and fetching 267 * as many instructions as possible. 268 */ 269 void tick(); 270 271 /** Checks all input signals and updates the status as necessary. 272 * @return: Returns if the status has changed due to input signals. 273 */ 274 bool checkSignalsAndUpdate(unsigned tid); 275 276 /** Does the actual fetching of instructions and passing them on to the 277 * next stage. 278 * @param status_change fetch() sets this variable if there was a status 279 * change (ie switching to IcacheMissStall). 280 */ 281 void fetch(bool &status_change); 282 283 /** Align a PC to the start of an I-cache block. */ 284 Addr icacheBlockAlignPC(Addr addr) 285 { 286 addr = TheISA::realPCToFetchPC(addr); 287 return (addr & ~(cacheBlkMask)); 288 } 289 290 private: 291 /** Handles retrying the fetch access. */ 292 void recvRetry(); 293 294 /** Returns the appropriate thread to fetch, given the fetch policy. */ 295 int getFetchingThread(FetchPriority &fetch_priority); 296 297 /** Returns the appropriate thread to fetch using a round robin policy. */ 298 int roundRobin(); 299 300 /** Returns the appropriate thread to fetch using the IQ count policy. */ 301 int iqCount(); 302 303 /** Returns the appropriate thread to fetch using the LSQ count policy. */ 304 int lsqCount(); 305 306 /** Returns the appropriate thread to fetch using the branch count policy. */ 307 int branchCount(); 308 309 private: 310 /** Pointer to the O3CPU. */ 311 O3CPU *cpu; 312 313 /** Time buffer interface. */ 314 TimeBuffer<TimeStruct> *timeBuffer; 315 316 /** Wire to get decode's information from backwards time buffer. */ 317 typename TimeBuffer<TimeStruct>::wire fromDecode; 318 319 /** Wire to get rename's information from backwards time buffer. */ 320 typename TimeBuffer<TimeStruct>::wire fromRename; 321 322 /** Wire to get iew's information from backwards time buffer. */ 323 typename TimeBuffer<TimeStruct>::wire fromIEW; 324 325 /** Wire to get commit's information from backwards time buffer. */ 326 typename TimeBuffer<TimeStruct>::wire fromCommit; 327 328 /** Internal fetch instruction queue. */ 329 TimeBuffer<FetchStruct> *fetchQueue; 330 331 //Might be annoying how this name is different than the queue. 332 /** Wire used to write any information heading to decode. */ 333 typename TimeBuffer<FetchStruct>::wire toDecode; 334 335 /** Icache interface. */ 336 IcachePort *icachePort; 337 338 /** BPredUnit. */ 339 BPredUnit branchPred; 340 341 /** Per-thread fetch PC. */ 342 Addr PC[Impl::MaxThreads]; 343 344 /** Per-thread next PC. */ 345 Addr nextPC[Impl::MaxThreads]; 346 347 /** Per-thread next Next PC. 348 * This is not a real register but is used for 349 * architectures that use a branch-delay slot. 350 * (such as MIPS or Sparc) 351 */ 352 Addr nextNPC[Impl::MaxThreads]; 353 354 /** Memory request used to access cache. */ 355 RequestPtr memReq[Impl::MaxThreads]; 356 357 /** Variable that tracks if fetch has written to the time buffer this 358 * cycle. Used to tell CPU if there is activity this cycle. 359 */ 360 bool wroteToTimeBuffer; 361 362 /** Tracks how many instructions has been fetched this cycle. */ 363 int numInst; 364 365 /** Tracks delay slot information for threads in ISAs which use 366 * delay slots; 367 */ 368 struct DelaySlotInfo { 369 InstSeqNum delaySlotSeqNum; 370 InstSeqNum branchSeqNum; 371 int numInsts; 372 Addr targetAddr; 373 bool targetReady; 374 }; 375 376 DelaySlotInfo delaySlotInfo[Impl::MaxThreads]; 377 378 /** Source of possible stalls. */ 379 struct Stalls { 380 bool decode; 381 bool rename; 382 bool iew; 383 bool commit; 384 }; 385 386 /** Tracks which stages are telling fetch to stall. */ 387 Stalls stalls[Impl::MaxThreads]; 388 389 /** Decode to fetch delay, in ticks. */ 390 unsigned decodeToFetchDelay; 391 392 /** Rename to fetch delay, in ticks. */ 393 unsigned renameToFetchDelay; 394 395 /** IEW to fetch delay, in ticks. */ 396 unsigned iewToFetchDelay; 397 398 /** Commit to fetch delay, in ticks. */ 399 unsigned commitToFetchDelay; 400 401 /** The width of fetch in instructions. */ 402 unsigned fetchWidth; 403 404 /** Is the cache blocked? If so no threads can access it. */ 405 bool cacheBlocked; 406 407 /** The packet that is waiting to be retried. */ 408 PacketPtr retryPkt; 409 410 /** The thread that is waiting on the cache to tell fetch to retry. */ 411 int retryTid; 412 413 /** Cache block size. */ 414 int cacheBlkSize; 415 416 /** Mask to get a cache block's address. */ 417 Addr cacheBlkMask; 418 419 /** The cache line being fetched. */ 420 uint8_t *cacheData[Impl::MaxThreads]; 421 422 /** The PC of the cacheline that has been loaded. */ 423 Addr cacheDataPC[Impl::MaxThreads]; 424 425 /** Whether or not the cache data is valid. */ 426 bool cacheDataValid[Impl::MaxThreads]; 427 428 /** Size of instructions. */ 429 int instSize; 430 431 /** Icache stall statistics. */ 432 Counter lastIcacheStall[Impl::MaxThreads]; 433 434 /** List of Active Threads */ 435 std::list<unsigned> *activeThreads; 436 437 /** Number of threads. */ 438 unsigned numThreads; 439 440 /** Number of threads that are actively fetching. */ 441 unsigned numFetchingThreads; 442 443 /** Thread ID being fetched. */ 444 int threadFetched; 445 446 /** Checks if there is an interrupt pending. If there is, fetch 447 * must stop once it is not fetching PAL instructions. 448 */ 449 bool interruptPending; 450 451 /** Is there a drain pending. */ 452 bool drainPending; 453 454 /** Records if fetch is switched out. */ 455 bool switchedOut; 456 457 // @todo: Consider making these vectors and tracking on a per thread basis. 458 /** Stat for total number of cycles stalled due to an icache miss. */ 459 Stats::Scalar<> icacheStallCycles; 460 /** Stat for total number of fetched instructions. */ 461 Stats::Scalar<> fetchedInsts; 462 /** Total number of fetched branches. */ 463 Stats::Scalar<> fetchedBranches; 464 /** Stat for total number of predicted branches. */ 465 Stats::Scalar<> predictedBranches; 466 /** Stat for total number of cycles spent fetching. */ 467 Stats::Scalar<> fetchCycles; 468 /** Stat for total number of cycles spent squashing. */ 469 Stats::Scalar<> fetchSquashCycles; 470 /** Stat for total number of cycles spent blocked due to other stages in 471 * the pipeline. 472 */ 473 Stats::Scalar<> fetchIdleCycles; 474 /** Total number of cycles spent blocked. */ 475 Stats::Scalar<> fetchBlockedCycles; 476 /** Total number of cycles spent in any other state. */ 477 Stats::Scalar<> fetchMiscStallCycles; 478 /** Stat for total number of fetched cache lines. */ 479 Stats::Scalar<> fetchedCacheLines; 480 /** Total number of outstanding icache accesses that were dropped 481 * due to a squash. 482 */ 483 Stats::Scalar<> fetchIcacheSquashes; 484 /** Distribution of number of instructions fetched each cycle. */ 485 Stats::Distribution<> fetchNisnDist; 486 /** Rate of how often fetch was idle. */ 487 Stats::Formula idleRate; 488 /** Number of branch fetches per cycle. */ 489 Stats::Formula branchRate; 490 /** Number of instruction fetched per cycle. */ 491 Stats::Formula fetchRate; 492}; 493 494#endif //__CPU_O3_FETCH_HH__ 495