summaryrefslogtreecommitdiff
path: root/cpu/o3/commit.hh
blob: 66abf8dc6b3e3c3ddf482098283c53d8cb2df0c6 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
/*
 * Copyright (c) 2004-2006 The Regents of The University of Michigan
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are
 * met: redistributions of source code must retain the above copyright
 * notice, this list of conditions and the following disclaimer;
 * redistributions in binary form must reproduce the above copyright
 * notice, this list of conditions and the following disclaimer in the
 * documentation and/or other materials provided with the distribution;
 * neither the name of the copyright holders nor the names of its
 * contributors may be used to endorse or promote products derived from
 * this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
 * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
 * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

#ifndef __CPU_O3_COMMIT_HH__
#define __CPU_O3_COMMIT_HH__

#include "arch/faults.hh"
#include "base/statistics.hh"
#include "base/timebuf.hh"
#include "cpu/exetrace.hh"
#include "cpu/inst_seq.hh"
#include "mem/memory_interface.hh"

template <class>
class O3ThreadState;

/**
 * DefaultCommit handles single threaded and SMT commit. Its width is
 * specified by the parameters; each cycle it tries to commit that
 * many instructions. The SMT policy decides which thread it tries to
 * commit instructions from. Non- speculative instructions must reach
 * the head of the ROB before they are ready to execute; once they
 * reach the head, commit will broadcast the instruction's sequence
 * number to the previous stages so that they can issue/ execute the
 * instruction. Only one non-speculative instruction is handled per
 * cycle. Commit is responsible for handling all back-end initiated
 * redirects.  It receives the redirect, and then broadcasts it to all
 * stages, indicating the sequence number they should squash until,
 * and any necessary branch misprediction information as well. It
 * priortizes redirects by instruction's age, only broadcasting a
 * redirect if it corresponds to an instruction that should currently
 * be in the ROB. This is done by tracking the sequence number of the
 * youngest instruction in the ROB, which gets updated to any
 * squashing instruction's sequence number, and only broadcasting a
 * redirect if it corresponds to an older instruction. Commit also
 * supports multiple cycle squashing, to model a ROB that can only
 * remove a certain number of instructions per cycle.
 */
template<class Impl>
class DefaultCommit
{
  public:
    // Typedefs from the Impl.
    typedef typename Impl::FullCPU FullCPU;
    typedef typename Impl::DynInstPtr DynInstPtr;
    typedef typename Impl::Params Params;
    typedef typename Impl::CPUPol CPUPol;

    typedef typename CPUPol::RenameMap RenameMap;
    typedef typename CPUPol::ROB ROB;

    typedef typename CPUPol::TimeStruct TimeStruct;
    typedef typename CPUPol::FetchStruct FetchStruct;
    typedef typename CPUPol::IEWStruct IEWStruct;
    typedef typename CPUPol::RenameStruct RenameStruct;

    typedef typename CPUPol::Fetch Fetch;
    typedef typename CPUPol::IEW IEW;

    typedef O3ThreadState<Impl> Thread;

    class TrapEvent : public Event {
      private:
        DefaultCommit<Impl> *commit;
        unsigned tid;

      public:
        TrapEvent(DefaultCommit<Impl> *_commit, unsigned _tid);

        void process();
        const char *description();
    };

    /** Overall commit status. Used to determine if the CPU can deschedule
     * itself due to a lack of activity.
     */
    enum CommitStatus{
        Active,
        Inactive
    };

    /** Individual thread status. */
    enum ThreadStatus {
        Running,
        Idle,
        ROBSquashing,
        TrapPending,
        FetchTrapPending
    };

    /** Commit policy for SMT mode. */
    enum CommitPolicy {
        Aggressive,
        RoundRobin,
        OldestReady
    };

  private:
    /** Overall commit status. */
    CommitStatus _status;
    /** Next commit status, to be set at the end of the cycle. */
    CommitStatus _nextStatus;
    /** Per-thread status. */
    ThreadStatus commitStatus[Impl::MaxThreads];
    /** Commit policy used in SMT mode. */
    CommitPolicy commitPolicy;

  public:
    /** Construct a DefaultCommit with the given parameters. */
    DefaultCommit(Params *params);

    /** Returns the name of the DefaultCommit. */
    std::string name() const;

    /** Registers statistics. */
    void regStats();

    /** Sets the CPU pointer. */
    void setCPU(FullCPU *cpu_ptr);

    /** Sets the list of threads. */
    void setThreads(std::vector<Thread *> &threads);

    /** Sets the main time buffer pointer, used for backwards communication. */
    void setTimeBuffer(TimeBuffer<TimeStruct> *tb_ptr);

    void setFetchQueue(TimeBuffer<FetchStruct> *fq_ptr);

    /** Sets the pointer to the queue coming from rename. */
    void setRenameQueue(TimeBuffer<RenameStruct> *rq_ptr);

    /** Sets the pointer to the queue coming from IEW. */
    void setIEWQueue(TimeBuffer<IEWStruct> *iq_ptr);

    void setFetchStage(Fetch *fetch_stage);

    Fetch *fetchStage;

    /** Sets the poitner to the IEW stage. */
    void setIEWStage(IEW *iew_stage);

    /** The pointer to the IEW stage. Used solely to ensure that
     * various events (traps, interrupts, syscalls) do not occur until
     * all stores have written back.
     */
    IEW *iewStage;

    /** Sets pointer to list of active threads. */
    void setActiveThreads(std::list<unsigned> *at_ptr);

    /** Sets pointer to the commited state rename map. */
    void setRenameMap(RenameMap rm_ptr[Impl::MaxThreads]);

    /** Sets pointer to the ROB. */
    void setROB(ROB *rob_ptr);

    /** Initializes stage by sending back the number of free entries. */
    void initStage();

    void switchOut();

    void doSwitchOut();

    void takeOverFrom();

    /** Ticks the commit stage, which tries to commit instructions. */
    void tick();

    /** Handles any squashes that are sent from IEW, and adds instructions
     * to the ROB and tries to commit instructions.
     */
    void commit();

    /** Returns the number of free ROB entries for a specific thread. */
    unsigned numROBFreeEntries(unsigned tid);

    void generateXCEvent(unsigned tid);

  private:
    /** Updates the overall status of commit with the nextStatus, and
     * tell the CPU if commit is active/inactive. */
    void updateStatus();

    /** Sets the next status based on threads' statuses, which becomes the
     * current status at the end of the cycle.
     */
    void setNextStatus();

    /** Checks if the ROB is completed with squashing. This is for the case
     * where the ROB can take multiple cycles to complete squashing.
     */
    bool robDoneSquashing();

    /** Returns if any of the threads have the number of ROB entries changed
     * on this cycle. Used to determine if the number of free ROB entries needs
     * to be sent back to previous stages.
     */
    bool changedROBEntries();

    void squashAll(unsigned tid);

    void squashFromTrap(unsigned tid);

    void squashFromXC(unsigned tid);

    /** Commits as many instructions as possible. */
    void commitInsts();

    /** Tries to commit the head ROB instruction passed in.
     * @param head_inst The instruction to be committed.
     */
    bool commitHead(DynInstPtr &head_inst, unsigned inst_num);

    void generateTrapEvent(unsigned tid);

    /** Gets instructions from rename and inserts them into the ROB. */
    void getInsts();

    /** Marks completed instructions using information sent from IEW. */
    void markCompletedInsts();

    /** Gets the thread to commit, based on the SMT policy. */
    int getCommittingThread();

    /** Returns the thread ID to use based on a round robin policy. */
    int roundRobin();

    /** Returns the thread ID to use based on an oldest instruction policy. */
    int oldestReady();

  public:
    /** Returns the PC of the head instruction of the ROB.
     * @todo: Probably remove this function as it returns only thread 0.
     */
    uint64_t readPC() { return PC[0]; }

    uint64_t readPC(unsigned tid) { return PC[tid]; }

    void setPC(uint64_t val, unsigned tid) { PC[tid] = val; }

    uint64_t readNextPC(unsigned tid) { return nextPC[tid]; }

    void setNextPC(uint64_t val, unsigned tid) { nextPC[tid] = val; }

  private:
    /** Time buffer interface. */
    TimeBuffer<TimeStruct> *timeBuffer;

    /** Wire to write information heading to previous stages. */
    typename TimeBuffer<TimeStruct>::wire toIEW;

    /** Wire to read information from IEW (for ROB). */
    typename TimeBuffer<TimeStruct>::wire robInfoFromIEW;

    TimeBuffer<FetchStruct> *fetchQueue;

    typename TimeBuffer<FetchStruct>::wire fromFetch;

    /** IEW instruction queue interface. */
    TimeBuffer<IEWStruct> *iewQueue;

    /** Wire to read information from IEW queue. */
    typename TimeBuffer<IEWStruct>::wire fromIEW;

    /** Rename instruction queue interface, for ROB. */
    TimeBuffer<RenameStruct> *renameQueue;

    /** Wire to read information from rename queue. */
    typename TimeBuffer<RenameStruct>::wire fromRename;

  public:
    /** ROB interface. */
    ROB *rob;

  private:
    /** Pointer to FullCPU. */
    FullCPU *cpu;

    /** Memory interface.  Used for d-cache accesses. */
    MemInterface *dcacheInterface;

    std::vector<Thread *> thread;

    Fault fetchFault;

    int fetchTrapWait;

    /** Records that commit has written to the time buffer this cycle. Used for
     * the CPU to determine if it can deschedule itself if there is no activity.
     */
    bool wroteToTimeBuffer;

    /** Records if the number of ROB entries has changed this cycle. If it has,
     * then the number of free entries must be re-broadcast.
     */
    bool changedROBNumEntries[Impl::MaxThreads];

    /** A counter of how many threads are currently squashing. */
    int squashCounter;

    /** Records if a thread has to squash this cycle due to a trap. */
    bool trapSquash[Impl::MaxThreads];

    /** Records if a thread has to squash this cycle due to an XC write. */
    bool xcSquash[Impl::MaxThreads];

    /** Priority List used for Commit Policy */
    std::list<unsigned> priority_list;

    /** IEW to Commit delay, in ticks. */
    unsigned iewToCommitDelay;

    /** Commit to IEW delay, in ticks. */
    unsigned commitToIEWDelay;

    /** Rename to ROB delay, in ticks. */
    unsigned renameToROBDelay;

    unsigned fetchToCommitDelay;

    /** Rename width, in instructions.  Used so ROB knows how many
     *  instructions to get from the rename instruction queue.
     */
    unsigned renameWidth;

    /** IEW width, in instructions.  Used so ROB knows how many
     *  instructions to get from the IEW instruction queue.
     */
    unsigned iewWidth;

    /** Commit width, in instructions. */
    unsigned commitWidth;

    /** Number of Reorder Buffers */
    unsigned numRobs;

    /** Number of Active Threads */
    unsigned numThreads;

    bool switchPending;
    bool switchedOut;

    Tick trapLatency;

    Tick fetchTrapLatency;

    Tick fetchFaultTick;

    Addr PC[Impl::MaxThreads];

    Addr nextPC[Impl::MaxThreads];

    /** The sequence number of the youngest valid instruction in the ROB. */
    InstSeqNum youngestSeqNum[Impl::MaxThreads];

    /** Pointer to the list of active threads. */
    std::list<unsigned> *activeThreads;

    /** Rename map interface. */
    RenameMap *renameMap[Impl::MaxThreads];

    void updateComInstStats(DynInstPtr &inst);

    /** Stat for the total number of committed instructions. */
    Stats::Scalar<> commitCommittedInsts;
    /** Stat for the total number of squashed instructions discarded by commit.
     */
    Stats::Scalar<> commitSquashedInsts;
    /** Stat for the total number of times commit is told to squash.
     * @todo: Actually increment this stat.
     */
    Stats::Scalar<> commitSquashEvents;
    /** Stat for the total number of times commit has had to stall due to a non-
     * speculative instruction reaching the head of the ROB.
     */
    Stats::Scalar<> commitNonSpecStalls;
    /** Stat for the total number of branch mispredicts that caused a squash. */
    Stats::Scalar<> branchMispredicts;
    /** Distribution of the number of committed instructions each cycle. */
    Stats::Distribution<> numCommittedDist;

    /** Total number of instructions committed. */
    Stats::Vector<> statComInst;
    /** Total number of software prefetches committed. */
    Stats::Vector<> statComSwp;
    /** Stat for the total number of committed memory references. */
    Stats::Vector<> statComRefs;
    /** Stat for the total number of committed loads. */
    Stats::Vector<> statComLoads;
    /** Total number of committed memory barriers. */
    Stats::Vector<> statComMembars;
    /** Total number of committed branches. */
    Stats::Vector<> statComBranches;

    Stats::Scalar<> commitEligibleSamples;
    Stats::Vector<> commitEligible;
};

#endif // __CPU_O3_COMMIT_HH__