src/mem/cache/mshr.hh

   1 /*
   2  * Copyright (c) 2012-2013, 2015-2016, 2018 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  * Copyright (c) 2002-2005 The Regents of The University of Michigan
  15  * All rights reserved.
  16  *
  17  * Redistribution and use in source and binary forms, with or without
  18  * modification, are permitted provided that the following conditions are
  19  * met: redistributions of source code must retain the above copyright
  20  * notice, this list of conditions and the following disclaimer;
  21  * redistributions in binary form must reproduce the above copyright
  22  * notice, this list of conditions and the following disclaimer in the
  23  * documentation and/or other materials provided with the distribution;
  24  * neither the name of the copyright holders nor the names of its
  25  * contributors may be used to endorse or promote products derived from
  26  * this software without specific prior written permission.
  27  *
  28  * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
  29  * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
  30  * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
  31  * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
  32  * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
  33  * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
  34  * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
  35  * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
  36  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  37  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  38  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  39  *
  40  * Authors: Erik Hallnor
  41  */
  42
  43 /**
  44  * @file
  45  * Miss Status and Handling Register (MSHR) declaration.
  46  */
  47
  48 #ifndef __MEM_CACHE_MSHR_HH__
  49 #define __MEM_CACHE_MSHR_HH__
  50
  51 #include <cassert>
  52 #include <iosfwd>
  53 #include <list>
  54 #include <string>
  55
  56 #include "base/printable.hh"
  57 #include "base/types.hh"
  58 #include "mem/cache/queue_entry.hh"
  59 #include "mem/packet.hh"
  60 #include "sim/core.hh"
  61
  62 class BaseCache;
  63
  64 /**
  65  * Miss Status and handling Register. This class keeps all the information
  66  * needed to handle a cache miss including a list of target requests.
  67  * @sa  \ref gem5MemorySystem "gem5 Memory System"
  68  */
  69 class MSHR : public QueueEntry, public Printable
  70 {
  71
  72     /**
  73      * Consider the queues friends to avoid making everything public.
  74      */
  75     template<typename Entry>
  76     friend class Queue;
  77     friend class MSHRQueue;
  78
  79   private:
  80
  81     /** Flag set by downstream caches */
  82     bool downstreamPending;
  83
  84     /**
  85      * Here we use one flag to track both if:
  86      *
  87      * 1. We are going to become owner or not, i.e., we will get the
  88      * block in an ownership state (Owned or Modified) with BlkDirty
  89      * set. This determines whether or not we are going to become the
  90      * responder and ordering point for future requests that we snoop.
  91      *
  92      * 2. We know that we are going to get a writable block, i.e. we
  93      * will get the block in writable state (Exclusive or Modified
  94      * state) with BlkWritable set. That determines whether additional
  95      * targets with needsWritable set will be able to be satisfied, or
  96      * if not should be put on the deferred list to possibly wait for
  97      * another request that does give us writable access.
  98      *
  99      * Condition 2 is actually just a shortcut that saves us from
 100      * possibly building a deferred target list and calling
 101      * promoteWritable() every time we get a writable block. Condition
 102      * 1, tracking ownership, is what is important. However, we never
 103      * receive ownership without marking the block dirty, and
 104      * consequently use pendingModified to track both ownership and
 105      * writability rather than having separate pendingDirty and
 106      * pendingWritable flags.
 107      */
 108     bool pendingModified;
 109
 110     /** Did we snoop an invalidate while waiting for data? */
 111     bool postInvalidate;
 112
 113     /** Did we snoop a read while waiting for data? */
 114     bool postDowngrade;
 115
 116   public:
 117
 118     /** True if the entry is just a simple forward from an upper level */
 119     bool isForward;
 120
 121     class Target {
 122       public:
 123
 124         enum Source {
 125             FromCPU,
 126             FromSnoop,
 127             FromPrefetcher
 128         };
 129
 130         const Tick recvTime;  //!< Time when request was received (for stats)
 131         const Tick readyTime; //!< Time when request is ready to be serviced
 132         const Counter order;  //!< Global order (for memory consistency mgmt)
 133         const PacketPtr pkt;  //!< Pending request packet.
 134         const Source source;  //!< Request from cpu, memory, or prefetcher?
 135
 136         /**
 137          * We use this flag to track whether we have cleared the
 138          * downstreamPending flag for the MSHR of the cache above
 139          * where this packet originates from and guard noninitial
 140          * attempts to clear it.
 141          *
 142          * The flag markedPending needs to be updated when the
 143          * TargetList is in service which can be:
 144          * 1) during the Target instantiation if the MSHR is in
 145          * service and the target is not deferred,
 146          * 2) when the MSHR becomes in service if the target is not
 147          * deferred,
 148          * 3) or when the TargetList is promoted (deferredTargets ->
 149          * targets).
 150          */
 151         bool markedPending;
 152
 153         const bool allocOnFill;   //!< Should the response servicing this
 154                                   //!< target list allocate in the cache?
 155
 156         Target(PacketPtr _pkt, Tick _readyTime, Counter _order,
 157                Source _source, bool _markedPending, bool alloc_on_fill)
 158             : recvTime(curTick()), readyTime(_readyTime), order(_order),
 159               pkt(_pkt), source(_source), markedPending(_markedPending),
 160               allocOnFill(alloc_on_fill)
 161         {}
 162     };
 163
 164     class TargetList : public std::list<Target> {
 165
 166       public:
 167         bool needsWritable;
 168         bool hasUpgrade;
 169         /** Set when the response should allocate on fill */
 170         bool allocOnFill;
 171         /**
 172          * Determine whether there was at least one non-snooping
 173          * target coming from another cache.
 174          */
 175         bool hasFromCache;
 176
 177         TargetList();
 178
 179         /**
 180          * Use the provided packet and the source to update the
 181          * flags of this TargetList.
 182          *
 183          * @param pkt Packet considered for the flag update
 184          * @param source Indicates the source of the packet
 185          * @param alloc_on_fill Whether the pkt would allocate on a fill
 186          */
 187         void updateFlags(PacketPtr pkt, Target::Source source,
 188                          bool alloc_on_fill);
 189
 190         void resetFlags() {
 191             needsWritable = false;
 192             hasUpgrade = false;
 193             allocOnFill = false;
 194             hasFromCache = false;
 195         }
 196
 197         /**
 198          * Goes through the list of targets and uses them to populate
 199          * the flags of this TargetList. When the function returns the
 200          * flags are consistent with the properties of packets in the
 201          * list.
 202          */
 203         void populateFlags();
 204
 205         /**
 206          * Tests if the flags of this TargetList have their default
 207          * values.
 208          */
 209         bool isReset() const {
 210             return !needsWritable && !hasUpgrade && !allocOnFill &&
 211                 !hasFromCache;
 212         }
 213
 214         /**
 215          * Add the specified packet in the TargetList. This function
 216          * stores information related to the added packet and updates
 217          * accordingly the flags.
 218          *
 219          * @param pkt Packet considered for adding
 220          * @param readTime Tick at which the packet is processed by this cache
 221          * @param order A counter giving a unique id to each target
 222          * @param source Indicates the source agent of the packet
 223          * @param markPending Set for deferred targets or pending MSHRs
 224          * @param alloc_on_fill Whether it should allocate on a fill
 225          */
 226         void add(PacketPtr pkt, Tick readyTime, Counter order,
 227                  Target::Source source, bool markPending,
 228                  bool alloc_on_fill);
 229
 230         /**
 231          * Convert upgrades to the equivalent request if the cache line they
 232          * refer to would have been invalid (Upgrade -> ReadEx, SC* -> Fail).
 233          * Used to rejig ordering between targets waiting on an MSHR. */
 234         void replaceUpgrades();
 235
 236         void clearDownstreamPending();
 237         bool checkFunctional(PacketPtr pkt);
 238         void print(std::ostream &os, int verbosity,
 239                    const std::string &prefix) const;
 240     };
 241
 242     /** A list of MSHRs. */
 243     typedef std::list<MSHR *> List;
 244     /** MSHR list iterator. */
 245     typedef List::iterator Iterator;
 246
 247     /** The pending* and post* flags are only valid if inService is
 248      *  true.  Using the accessor functions lets us detect if these
 249      *  flags are accessed improperly.
 250      */
 251
 252     /** True if we need to get a writable copy of the block. */
 253     bool needsWritable() const { return targets.needsWritable; }
 254
 255     bool isCleaning() const {
 256         PacketPtr pkt = targets.front().pkt;
 257         return pkt->isClean();
 258     }
 259
 260     bool isPendingModified() const {
 261         assert(inService); return pendingModified;
 262     }
 263
 264     bool hasPostInvalidate() const {
 265         assert(inService); return postInvalidate;
 266     }
 267
 268     bool hasPostDowngrade() const {
 269         assert(inService); return postDowngrade;
 270     }
 271
 272     bool sendPacket(BaseCache &cache);
 273
 274     bool allocOnFill() const {
 275         return targets.allocOnFill;
 276     }
 277
 278     /**
 279      * Determine if there are non-deferred requests from other caches
 280      *
 281      * @return true if any of the targets is from another cache
 282      */
 283     bool hasFromCache() const {
 284         return targets.hasFromCache;
 285     }
 286
 287   private:
 288
 289     /**
 290      * Pointer to this MSHR on the ready list.
 291      * @sa MissQueue, MSHRQueue::readyList
 292      */
 293     Iterator readyIter;
 294
 295     /**
 296      * Pointer to this MSHR on the allocated list.
 297      * @sa MissQueue, MSHRQueue::allocatedList
 298      */
 299     Iterator allocIter;
 300
 301     /** List of all requests that match the address */
 302     TargetList targets;
 303
 304     TargetList deferredTargets;
 305
 306   public:
 307
 308     /**
 309      * Allocate a miss to this MSHR.
 310      * @param blk_addr The address of the block.
 311      * @param blk_size The number of bytes to request.
 312      * @param pkt The original miss.
 313      * @param when_ready When should the MSHR be ready to act upon.
 314      * @param _order The logical order of this MSHR
 315      * @param alloc_on_fill Should the cache allocate a block on fill
 316      */
 317     void allocate(Addr blk_addr, unsigned blk_size, PacketPtr pkt,
 318                   Tick when_ready, Counter _order, bool alloc_on_fill);
 319
 320     void markInService(bool pending_modified_resp);
 321
 322     void clearDownstreamPending();
 323
 324     /**
 325      * Mark this MSHR as free.
 326      */
 327     void deallocate();
 328
 329     /**
 330      * Add a request to the list of targets.
 331      * @param target The target.
 332      */
 333     void allocateTarget(PacketPtr target, Tick when, Counter order,
 334                         bool alloc_on_fill);
 335     bool handleSnoop(PacketPtr target, Counter order);
 336
 337     /** A simple constructor. */
 338     MSHR();
 339
 340     /**
 341      * Returns the current number of allocated targets.
 342      * @return The current number of allocated targets.
 343      */
 344     int getNumTargets() const
 345     { return targets.size() + deferredTargets.size(); }
 346
 347     /**
 348      * Extracts the subset of the targets that can be serviced given a
 349      * received response. This function returns the targets list
 350      * unless the response is a ReadRespWithInvalidate. The
 351      * ReadRespWithInvalidate is only invalidating response that its
 352      * invalidation was not expected when the request (a
 353      * ReadSharedReq) was sent out. For ReadRespWithInvalidate we can
 354      * safely service only the first FromCPU target and all FromSnoop
 355      * targets (inform all snoopers that we no longer have the block).
 356      *
 357      * @param pkt The response from the downstream memory
 358      */
 359     TargetList extractServiceableTargets(PacketPtr pkt);
 360
 361     /**
 362      * Returns true if there are targets left.
 363      * @return true if there are targets
 364      */
 365     bool hasTargets() const { return !targets.empty(); }
 366
 367     /**
 368      * Returns a reference to the first target.
 369      * @return A pointer to the first target.
 370      */
 371     Target *getTarget()
 372     {
 373         assert(hasTargets());
 374         return &targets.front();
 375     }
 376
 377     /**
 378      * Pop first target.
 379      */
 380     void popTarget()
 381     {
 382         targets.pop_front();
 383     }
 384
 385     bool promoteDeferredTargets();
 386
 387     void promoteWritable();
 388
 389     bool checkFunctional(PacketPtr pkt);
 390
 391     /**
 392      * Prints the contents of this MSHR for debugging.
 393      */
 394     void print(std::ostream &os,
 395                int verbosity = 0,
 396                const std::string &prefix = "") const;
 397     /**
 398      * A no-args wrapper of print(std::ostream...)  meant to be
 399      * invoked from DPRINTFs avoiding string overheads in fast mode
 400      *
 401      * @return string with mshr fields + [deferred]targets
 402      */
 403     std::string print() const;
 404 };
 405
 406 #endif // __MEM_CACHE_MSHR_HH__