src/mem/cache/mshr.hh

   1 /*
   2  * Copyright (c) 2012-2013, 2015-2016 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 <list>
  52
  53 #include "base/printable.hh"
  54 #include "mem/cache/queue_entry.hh"
  55
  56 class Cache;
  57
  58 /**
  59  * Miss Status and handling Register. This class keeps all the information
  60  * needed to handle a cache miss including a list of target requests.
  61  * @sa  \ref gem5MemorySystem "gem5 Memory System"
  62  */
  63 class MSHR : public QueueEntry, public Printable
  64 {
  65
  66     /**
  67      * Consider the queues friends to avoid making everything public.
  68      */
  69     template<typename Entry>
  70     friend class Queue;
  71     friend class MSHRQueue;
  72
  73   private:
  74
  75     /** Flag set by downstream caches */
  76     bool downstreamPending;
  77
  78     /**
  79      * Here we use one flag to track both if:
  80      *
  81      * 1. We are going to become owner or not, i.e., we will get the
  82      * block in an ownership state (Owned or Modified) with BlkDirty
  83      * set. This determines whether or not we are going to become the
  84      * responder and ordering point for future requests that we snoop.
  85      *
  86      * 2. We know that we are going to get a writable block, i.e. we
  87      * will get the block in writable state (Exclusive or Modified
  88      * state) with BlkWritable set. That determines whether additional
  89      * targets with needsWritable set will be able to be satisfied, or
  90      * if not should be put on the deferred list to possibly wait for
  91      * another request that does give us writable access.
  92      *
  93      * Condition 2 is actually just a shortcut that saves us from
  94      * possibly building a deferred target list and calling
  95      * promoteWritable() every time we get a writable block. Condition
  96      * 1, tracking ownership, is what is important. However, we never
  97      * receive ownership without marking the block dirty, and
  98      * consequently use pendingModified to track both ownership and
  99      * writability rather than having separate pendingDirty and
 100      * pendingWritable flags.
 101      */
 102     bool pendingModified;
 103
 104     /** Did we snoop an invalidate while waiting for data? */
 105     bool postInvalidate;
 106
 107     /** Did we snoop a read while waiting for data? */
 108     bool postDowngrade;
 109
 110   public:
 111
 112     /** True if the entry is just a simple forward from an upper level */
 113     bool isForward;
 114
 115     class Target {
 116       public:
 117
 118         enum Source {
 119             FromCPU,
 120             FromSnoop,
 121             FromPrefetcher
 122         };
 123
 124         const Tick recvTime;  //!< Time when request was received (for stats)
 125         const Tick readyTime; //!< Time when request is ready to be serviced
 126         const Counter order;  //!< Global order (for memory consistency mgmt)
 127         const PacketPtr pkt;  //!< Pending request packet.
 128         const Source source;  //!< Request from cpu, memory, or prefetcher?
 129
 130         /**
 131          * We use this flag to track whether we have cleared the
 132          * downstreamPending flag for the MSHR of the cache above
 133          * where this packet originates from and guard noninitial
 134          * attempts to clear it.
 135          *
 136          * The flag markedPending needs to be updated when the
 137          * TargetList is in service which can be:
 138          * 1) during the Target instantiation if the MSHR is in
 139          * service and the target is not deferred,
 140          * 2) when the MSHR becomes in service if the target is not
 141          * deferred,
 142          * 3) or when the TargetList is promoted (deferredTargets ->
 143          * targets).
 144          */
 145         bool markedPending;
 146
 147         const bool allocOnFill;   //!< Should the response servicing this
 148                                   //!< target list allocate in the cache?
 149
 150         Target(PacketPtr _pkt, Tick _readyTime, Counter _order,
 151                Source _source, bool _markedPending, bool alloc_on_fill)
 152             : recvTime(curTick()), readyTime(_readyTime), order(_order),
 153               pkt(_pkt), source(_source), markedPending(_markedPending),
 154               allocOnFill(alloc_on_fill)
 155         {}
 156     };
 157
 158     class TargetList : public std::list<Target> {
 159
 160       public:
 161         bool needsWritable;
 162         bool hasUpgrade;
 163         /** Set when the response should allocate on fill */
 164         bool allocOnFill;
 165
 166         TargetList();
 167
 168         /**
 169          * Use the provided packet and the source to update the
 170          * flags of this TargetList.
 171          *
 172          * @param pkt Packet considered for the flag update
 173          * @param source Indicates the source of the packet
 174          * @param alloc_on_fill Whether the pkt would allocate on a fill
 175          */
 176         void updateFlags(PacketPtr pkt, Target::Source source,
 177                          bool alloc_on_fill);
 178
 179         void resetFlags() { needsWritable = hasUpgrade = allocOnFill = false; }
 180
 181         /**
 182          * Goes through the list of targets and uses them to populate
 183          * the flags of this TargetList. When the function returns the
 184          * flags are consistent with the properties of packets in the
 185          * list.
 186          */
 187         void populateFlags();
 188
 189         /**
 190          * Tests if the flags of this TargetList have their default
 191          * values.
 192          */
 193         bool isReset() const {
 194             return !needsWritable && !hasUpgrade && !allocOnFill;
 195         }
 196
 197         /**
 198          * Add the specified packet in the TargetList. This function
 199          * stores information related to the added packet and updates
 200          * accordingly the flags.
 201          *
 202          * @param pkt Packet considered for adding
 203          * @param readTime Tick at which the packet is processed by this cache
 204          * @param order A counter giving a unique id to each target
 205          * @param source Indicates the source agent of the packet
 206          * @param markPending Set for deferred targets or pending MSHRs
 207          * @param alloc_on_fill Whether it should allocate on a fill
 208          */
 209         void add(PacketPtr pkt, Tick readyTime, Counter order,
 210                  Target::Source source, bool markPending,
 211                  bool alloc_on_fill);
 212
 213         /**
 214          * Convert upgrades to the equivalent request if the cache line they
 215          * refer to would have been invalid (Upgrade -> ReadEx, SC* -> Fail).
 216          * Used to rejig ordering between targets waiting on an MSHR. */
 217         void replaceUpgrades();
 218
 219         void clearDownstreamPending();
 220         bool checkFunctional(PacketPtr pkt);
 221         void print(std::ostream &os, int verbosity,
 222                    const std::string &prefix) const;
 223     };
 224
 225     /** A list of MSHRs. */
 226     typedef std::list<MSHR *> List;
 227     /** MSHR list iterator. */
 228     typedef List::iterator Iterator;
 229
 230     /** The pending* and post* flags are only valid if inService is
 231      *  true.  Using the accessor functions lets us detect if these
 232      *  flags are accessed improperly.
 233      */
 234
 235     /** True if we need to get a writable copy of the block. */
 236     bool needsWritable() const { return targets.needsWritable; }
 237
 238     bool isPendingModified() const {
 239         assert(inService); return pendingModified;
 240     }
 241
 242     bool hasPostInvalidate() const {
 243         assert(inService); return postInvalidate;
 244     }
 245
 246     bool hasPostDowngrade() const {
 247         assert(inService); return postDowngrade;
 248     }
 249
 250     bool sendPacket(Cache &cache);
 251
 252     bool allocOnFill() const {
 253         return targets.allocOnFill;
 254     }
 255   private:
 256
 257     /**
 258      * Pointer to this MSHR on the ready list.
 259      * @sa MissQueue, MSHRQueue::readyList
 260      */
 261     Iterator readyIter;
 262
 263     /**
 264      * Pointer to this MSHR on the allocated list.
 265      * @sa MissQueue, MSHRQueue::allocatedList
 266      */
 267     Iterator allocIter;
 268
 269     /** List of all requests that match the address */
 270     TargetList targets;
 271
 272     TargetList deferredTargets;
 273
 274   public:
 275
 276     /**
 277      * Allocate a miss to this MSHR.
 278      * @param blk_addr The address of the block.
 279      * @param blk_size The number of bytes to request.
 280      * @param pkt The original miss.
 281      * @param when_ready When should the MSHR be ready to act upon.
 282      * @param _order The logical order of this MSHR
 283      * @param alloc_on_fill Should the cache allocate a block on fill
 284      */
 285     void allocate(Addr blk_addr, unsigned blk_size, PacketPtr pkt,
 286                   Tick when_ready, Counter _order, bool alloc_on_fill);
 287
 288     void markInService(bool pending_modified_resp);
 289
 290     void clearDownstreamPending();
 291
 292     /**
 293      * Mark this MSHR as free.
 294      */
 295     void deallocate();
 296
 297     /**
 298      * Add a request to the list of targets.
 299      * @param target The target.
 300      */
 301     void allocateTarget(PacketPtr target, Tick when, Counter order,
 302                         bool alloc_on_fill);
 303     bool handleSnoop(PacketPtr target, Counter order);
 304
 305     /** A simple constructor. */
 306     MSHR();
 307
 308     /**
 309      * Returns the current number of allocated targets.
 310      * @return The current number of allocated targets.
 311      */
 312     int getNumTargets() const
 313     { return targets.size() + deferredTargets.size(); }
 314
 315     /**
 316      * Extracts the subset of the targets that can be serviced given a
 317      * received response. This function returns the targets list
 318      * unless the response is a ReadRespWithInvalidate. The
 319      * ReadRespWithInvalidate is only invalidating response that its
 320      * invalidation was not expected when the request (a
 321      * ReadSharedReq) was sent out. For ReadRespWithInvalidate we can
 322      * safely service only the first FromCPU target and all FromSnoop
 323      * targets (inform all snoopers that we no longer have the block).
 324      *
 325      * @param pkt The response from the downstream memory
 326      */
 327     TargetList extractServiceableTargets(PacketPtr pkt);
 328
 329     /**
 330      * Returns true if there are targets left.
 331      * @return true if there are targets
 332      */
 333     bool hasTargets() const { return !targets.empty(); }
 334
 335     /**
 336      * Returns a reference to the first target.
 337      * @return A pointer to the first target.
 338      */
 339     Target *getTarget()
 340     {
 341         assert(hasTargets());
 342         return &targets.front();
 343     }
 344
 345     /**
 346      * Pop first target.
 347      */
 348     void popTarget()
 349     {
 350         targets.pop_front();
 351     }
 352
 353     bool promoteDeferredTargets();
 354
 355     void promoteWritable();
 356
 357     bool checkFunctional(PacketPtr pkt);
 358
 359     /**
 360      * Prints the contents of this MSHR for debugging.
 361      */
 362     void print(std::ostream &os,
 363                int verbosity = 0,
 364                const std::string &prefix = "") const;
 365     /**
 366      * A no-args wrapper of print(std::ostream...)  meant to be
 367      * invoked from DPRINTFs avoiding string overheads in fast mode
 368      *
 369      * @return string with mshr fields + [deferred]targets
 370      */
 371     std::string print() const;
 372 };
 373
 374 #endif // __MEM_CACHE_MSHR_HH__