mshr.hh revision 12599:43ade6cf92b7
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 <list>
52
53#include "base/printable.hh"
54#include "mem/cache/queue_entry.hh"
55
56class 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 */
63class 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 isCleaning() const {
239        PacketPtr pkt = targets.front().pkt;
240        return pkt->isClean();
241    }
242
243    bool isPendingModified() const {
244        assert(inService); return pendingModified;
245    }
246
247    bool hasPostInvalidate() const {
248        assert(inService); return postInvalidate;
249    }
250
251    bool hasPostDowngrade() const {
252        assert(inService); return postDowngrade;
253    }
254
255    bool sendPacket(Cache &cache);
256
257    bool allocOnFill() const {
258        return targets.allocOnFill;
259    }
260  private:
261
262    /**
263     * Pointer to this MSHR on the ready list.
264     * @sa MissQueue, MSHRQueue::readyList
265     */
266    Iterator readyIter;
267
268    /**
269     * Pointer to this MSHR on the allocated list.
270     * @sa MissQueue, MSHRQueue::allocatedList
271     */
272    Iterator allocIter;
273
274    /** List of all requests that match the address */
275    TargetList targets;
276
277    TargetList deferredTargets;
278
279  public:
280
281    /**
282     * Allocate a miss to this MSHR.
283     * @param blk_addr The address of the block.
284     * @param blk_size The number of bytes to request.
285     * @param pkt The original miss.
286     * @param when_ready When should the MSHR be ready to act upon.
287     * @param _order The logical order of this MSHR
288     * @param alloc_on_fill Should the cache allocate a block on fill
289     */
290    void allocate(Addr blk_addr, unsigned blk_size, PacketPtr pkt,
291                  Tick when_ready, Counter _order, bool alloc_on_fill);
292
293    void markInService(bool pending_modified_resp);
294
295    void clearDownstreamPending();
296
297    /**
298     * Mark this MSHR as free.
299     */
300    void deallocate();
301
302    /**
303     * Add a request to the list of targets.
304     * @param target The target.
305     */
306    void allocateTarget(PacketPtr target, Tick when, Counter order,
307                        bool alloc_on_fill);
308    bool handleSnoop(PacketPtr target, Counter order);
309
310    /** A simple constructor. */
311    MSHR();
312
313    /**
314     * Returns the current number of allocated targets.
315     * @return The current number of allocated targets.
316     */
317    int getNumTargets() const
318    { return targets.size() + deferredTargets.size(); }
319
320    /**
321     * Extracts the subset of the targets that can be serviced given a
322     * received response. This function returns the targets list
323     * unless the response is a ReadRespWithInvalidate. The
324     * ReadRespWithInvalidate is only invalidating response that its
325     * invalidation was not expected when the request (a
326     * ReadSharedReq) was sent out. For ReadRespWithInvalidate we can
327     * safely service only the first FromCPU target and all FromSnoop
328     * targets (inform all snoopers that we no longer have the block).
329     *
330     * @param pkt The response from the downstream memory
331     */
332    TargetList extractServiceableTargets(PacketPtr pkt);
333
334    /**
335     * Returns true if there are targets left.
336     * @return true if there are targets
337     */
338    bool hasTargets() const { return !targets.empty(); }
339
340    /**
341     * Returns a reference to the first target.
342     * @return A pointer to the first target.
343     */
344    Target *getTarget()
345    {
346        assert(hasTargets());
347        return &targets.front();
348    }
349
350    /**
351     * Pop first target.
352     */
353    void popTarget()
354    {
355        targets.pop_front();
356    }
357
358    bool promoteDeferredTargets();
359
360    void promoteWritable();
361
362    bool checkFunctional(PacketPtr pkt);
363
364    /**
365     * Prints the contents of this MSHR for debugging.
366     */
367    void print(std::ostream &os,
368               int verbosity = 0,
369               const std::string &prefix = "") const;
370    /**
371     * A no-args wrapper of print(std::ostream...)  meant to be
372     * invoked from DPRINTFs avoiding string overheads in fast mode
373     *
374     * @return string with mshr fields + [deferred]targets
375     */
376    std::string print() const;
377};
378
379#endif // __MEM_CACHE_MSHR_HH__
380