mshr.hh revision 12792:9af3470e24e7
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
62class 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 */
69class 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        void clearDownstreamPending(iterator begin, iterator end);
238        bool checkFunctional(PacketPtr pkt);
239        void print(std::ostream &os, int verbosity,
240                   const std::string &prefix) const;
241    };
242
243    /** A list of MSHRs. */
244    typedef std::list<MSHR *> List;
245    /** MSHR list iterator. */
246    typedef List::iterator Iterator;
247
248    /** The pending* and post* flags are only valid if inService is
249     *  true.  Using the accessor functions lets us detect if these
250     *  flags are accessed improperly.
251     */
252
253    /** True if we need to get a writable copy of the block. */
254    bool needsWritable() const { return targets.needsWritable; }
255
256    bool isCleaning() const {
257        PacketPtr pkt = targets.front().pkt;
258        return pkt->isClean();
259    }
260
261    bool isPendingModified() const {
262        assert(inService); return pendingModified;
263    }
264
265    bool hasPostInvalidate() const {
266        assert(inService); return postInvalidate;
267    }
268
269    bool hasPostDowngrade() const {
270        assert(inService); return postDowngrade;
271    }
272
273    bool sendPacket(BaseCache &cache);
274
275    bool allocOnFill() const {
276        return targets.allocOnFill;
277    }
278
279    /**
280     * Determine if there are non-deferred requests from other caches
281     *
282     * @return true if any of the targets is from another cache
283     */
284    bool hasFromCache() const {
285        return targets.hasFromCache;
286    }
287
288  private:
289
290    /**
291     * Pointer to this MSHR on the ready list.
292     * @sa MissQueue, MSHRQueue::readyList
293     */
294    Iterator readyIter;
295
296    /**
297     * Pointer to this MSHR on the allocated list.
298     * @sa MissQueue, MSHRQueue::allocatedList
299     */
300    Iterator allocIter;
301
302    /** List of all requests that match the address */
303    TargetList targets;
304
305    TargetList deferredTargets;
306
307  public:
308
309    /**
310     * Allocate a miss to this MSHR.
311     * @param blk_addr The address of the block.
312     * @param blk_size The number of bytes to request.
313     * @param pkt The original miss.
314     * @param when_ready When should the MSHR be ready to act upon.
315     * @param _order The logical order of this MSHR
316     * @param alloc_on_fill Should the cache allocate a block on fill
317     */
318    void allocate(Addr blk_addr, unsigned blk_size, PacketPtr pkt,
319                  Tick when_ready, Counter _order, bool alloc_on_fill);
320
321    void markInService(bool pending_modified_resp);
322
323    void clearDownstreamPending();
324
325    /**
326     * Mark this MSHR as free.
327     */
328    void deallocate();
329
330    /**
331     * Add a request to the list of targets.
332     * @param target The target.
333     */
334    void allocateTarget(PacketPtr target, Tick when, Counter order,
335                        bool alloc_on_fill);
336    bool handleSnoop(PacketPtr target, Counter order);
337
338    /** A simple constructor. */
339    MSHR();
340
341    /**
342     * Returns the current number of allocated targets.
343     * @return The current number of allocated targets.
344     */
345    int getNumTargets() const
346    { return targets.size() + deferredTargets.size(); }
347
348    /**
349     * Extracts the subset of the targets that can be serviced given a
350     * received response. This function returns the targets list
351     * unless the response is a ReadRespWithInvalidate. The
352     * ReadRespWithInvalidate is only invalidating response that its
353     * invalidation was not expected when the request (a
354     * ReadSharedReq) was sent out. For ReadRespWithInvalidate we can
355     * safely service only the first FromCPU target and all FromSnoop
356     * targets (inform all snoopers that we no longer have the block).
357     *
358     * @param pkt The response from the downstream memory
359     */
360    TargetList extractServiceableTargets(PacketPtr pkt);
361
362    /**
363     * Returns true if there are targets left.
364     * @return true if there are targets
365     */
366    bool hasTargets() const { return !targets.empty(); }
367
368    /**
369     * Returns a reference to the first target.
370     * @return A pointer to the first target.
371     */
372    Target *getTarget()
373    {
374        assert(hasTargets());
375        return &targets.front();
376    }
377
378    /**
379     * Pop first target.
380     */
381    void popTarget()
382    {
383        targets.pop_front();
384    }
385
386    bool promoteDeferredTargets();
387
388    /**
389     * Promotes deferred targets that do not require writable
390     *
391     * Requests in the deferred target list are moved to the target
392     * list up until the first target that is a cache maintenance
393     * operation or needs a writable copy of the block
394     */
395    void promoteWritable();
396
397    bool checkFunctional(PacketPtr pkt);
398
399    /**
400     * Prints the contents of this MSHR for debugging.
401     */
402    void print(std::ostream &os,
403               int verbosity = 0,
404               const std::string &prefix = "") const;
405    /**
406     * A no-args wrapper of print(std::ostream...)  meant to be
407     * invoked from DPRINTFs avoiding string overheads in fast mode
408     *
409     * @return string with mshr fields + [deferred]targets
410     */
411    std::string print() const;
412};
413
414#endif // __MEM_CACHE_MSHR_HH__
415