rename.hh revision 12106
1/*
2 * Copyright (c) 2012 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) 2004-2006 The Regents of The University of Michigan
15 * Copyright (c) 2013 Advanced Micro Devices, Inc.
16 * All rights reserved.
17 *
18 * Redistribution and use in source and binary forms, with or without
19 * modification, are permitted provided that the following conditions are
20 * met: redistributions of source code must retain the above copyright
21 * notice, this list of conditions and the following disclaimer;
22 * redistributions in binary form must reproduce the above copyright
23 * notice, this list of conditions and the following disclaimer in the
24 * documentation and/or other materials provided with the distribution;
25 * neither the name of the copyright holders nor the names of its
26 * contributors may be used to endorse or promote products derived from
27 * this software without specific prior written permission.
28 *
29 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
30 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
31 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
32 * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
33 * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
34 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
35 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
36 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
37 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
38 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
39 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
40 *
41 * Authors: Kevin Lim
42 */
43
44#ifndef __CPU_O3_RENAME_HH__
45#define __CPU_O3_RENAME_HH__
46
47#include <list>
48#include <utility>
49
50#include "base/statistics.hh"
51#include "config/the_isa.hh"
52#include "cpu/timebuf.hh"
53#include "sim/probe/probe.hh"
54
55struct DerivO3CPUParams;
56
57/**
58 * DefaultRename handles both single threaded and SMT rename. Its
59 * width is specified by the parameters; each cycle it tries to rename
60 * that many instructions. It holds onto the rename history of all
61 * instructions with destination registers, storing the
62 * arch. register, the new physical register, and the old physical
63 * register, to allow for undoing of mappings if squashing happens, or
64 * freeing up registers upon commit. Rename handles blocking if the
65 * ROB, IQ, or LSQ is going to be full. Rename also handles barriers,
66 * and does so by stalling on the instruction until the ROB is empty
67 * and there are no instructions in flight to the ROB.
68 */
69template<class Impl>
70class DefaultRename
71{
72  public:
73    // Typedefs from the Impl.
74    typedef typename Impl::CPUPol CPUPol;
75    typedef typename Impl::DynInstPtr DynInstPtr;
76    typedef typename Impl::O3CPU O3CPU;
77
78    // Typedefs from the CPUPol
79    typedef typename CPUPol::DecodeStruct DecodeStruct;
80    typedef typename CPUPol::RenameStruct RenameStruct;
81    typedef typename CPUPol::TimeStruct TimeStruct;
82    typedef typename CPUPol::FreeList FreeList;
83    typedef typename CPUPol::RenameMap RenameMap;
84    // These are used only for initialization.
85    typedef typename CPUPol::IEW IEW;
86    typedef typename CPUPol::Commit Commit;
87
88    // A deque is used to queue the instructions. Barrier insts must
89    // be added to the front of the queue, which is the only reason for
90    // using a deque instead of a queue. (Most other stages use a
91    // queue)
92    typedef std::deque<DynInstPtr> InstQueue;
93
94  public:
95    /** Overall rename status. Used to determine if the CPU can
96     * deschedule itself due to a lack of activity.
97     */
98    enum RenameStatus {
99        Active,
100        Inactive
101    };
102
103    /** Individual thread status. */
104    enum ThreadStatus {
105        Running,
106        Idle,
107        StartSquash,
108        Squashing,
109        Blocked,
110        Unblocking,
111        SerializeStall
112    };
113
114  private:
115    /** Rename status. */
116    RenameStatus _status;
117
118    /** Per-thread status. */
119    ThreadStatus renameStatus[Impl::MaxThreads];
120
121    /** Probe points. */
122    typedef typename std::pair<InstSeqNum, PhysRegIdPtr> SeqNumRegPair;
123    /** To probe when register renaming for an instruction is complete */
124    ProbePointArg<DynInstPtr> *ppRename;
125    /**
126     * To probe when an instruction is squashed and the register mapping
127     * for it needs to be undone
128     */
129    ProbePointArg<SeqNumRegPair> *ppSquashInRename;
130
131  public:
132    /** DefaultRename constructor. */
133    DefaultRename(O3CPU *_cpu, DerivO3CPUParams *params);
134
135    /** Returns the name of rename. */
136    std::string name() const;
137
138    /** Registers statistics. */
139    void regStats();
140
141    /** Registers probes. */
142    void regProbePoints();
143
144    /** Sets the main backwards communication time buffer pointer. */
145    void setTimeBuffer(TimeBuffer<TimeStruct> *tb_ptr);
146
147    /** Sets pointer to time buffer used to communicate to the next stage. */
148    void setRenameQueue(TimeBuffer<RenameStruct> *rq_ptr);
149
150    /** Sets pointer to time buffer coming from decode. */
151    void setDecodeQueue(TimeBuffer<DecodeStruct> *dq_ptr);
152
153    /** Sets pointer to IEW stage. Used only for initialization. */
154    void setIEWStage(IEW *iew_stage)
155    { iew_ptr = iew_stage; }
156
157    /** Sets pointer to commit stage. Used only for initialization. */
158    void setCommitStage(Commit *commit_stage)
159    { commit_ptr = commit_stage; }
160
161  private:
162    /** Pointer to IEW stage. Used only for initialization. */
163    IEW *iew_ptr;
164
165    /** Pointer to commit stage. Used only for initialization. */
166    Commit *commit_ptr;
167
168  public:
169    /** Initializes variables for the stage. */
170    void startupStage();
171
172    /** Sets pointer to list of active threads. */
173    void setActiveThreads(std::list<ThreadID> *at_ptr);
174
175    /** Sets pointer to rename maps (per-thread structures). */
176    void setRenameMap(RenameMap rm_ptr[Impl::MaxThreads]);
177
178    /** Sets pointer to the free list. */
179    void setFreeList(FreeList *fl_ptr);
180
181    /** Sets pointer to the scoreboard. */
182    void setScoreboard(Scoreboard *_scoreboard);
183
184    /** Perform sanity checks after a drain. */
185    void drainSanityCheck() const;
186
187    /** Has the stage drained? */
188    bool isDrained() const;
189
190    /** Takes over from another CPU's thread. */
191    void takeOverFrom();
192
193    /** Squashes all instructions in a thread. */
194    void squash(const InstSeqNum &squash_seq_num, ThreadID tid);
195
196    /** Ticks rename, which processes all input signals and attempts to rename
197     * as many instructions as possible.
198     */
199    void tick();
200
201    /** Debugging function used to dump history buffer of renamings. */
202    void dumpHistory();
203
204  private:
205    /** Reset this pipeline stage */
206    void resetStage();
207
208    /** Determines what to do based on rename's current status.
209     * @param status_change rename() sets this variable if there was a status
210     * change (ie switching from blocking to unblocking).
211     * @param tid Thread id to rename instructions from.
212     */
213    void rename(bool &status_change, ThreadID tid);
214
215    /** Renames instructions for the given thread. Also handles serializing
216     * instructions.
217     */
218    void renameInsts(ThreadID tid);
219
220    /** Inserts unused instructions from a given thread into the skid buffer,
221     * to be renamed once rename unblocks.
222     */
223    void skidInsert(ThreadID tid);
224
225    /** Separates instructions from decode into individual lists of instructions
226     * sorted by thread.
227     */
228    void sortInsts();
229
230    /** Returns if all of the skid buffers are empty. */
231    bool skidsEmpty();
232
233    /** Updates overall rename status based on all of the threads' statuses. */
234    void updateStatus();
235
236    /** Switches rename to blocking, and signals back that rename has become
237     * blocked.
238     * @return Returns true if there is a status change.
239     */
240    bool block(ThreadID tid);
241
242    /** Switches rename to unblocking if the skid buffer is empty, and signals
243     * back that rename has unblocked.
244     * @return Returns true if there is a status change.
245     */
246    bool unblock(ThreadID tid);
247
248    /** Executes actual squash, removing squashed instructions. */
249    void doSquash(const InstSeqNum &squash_seq_num, ThreadID tid);
250
251    /** Removes a committed instruction's rename history. */
252    void removeFromHistory(InstSeqNum inst_seq_num, ThreadID tid);
253
254    /** Renames the source registers of an instruction. */
255    inline void renameSrcRegs(DynInstPtr &inst, ThreadID tid);
256
257    /** Renames the destination registers of an instruction. */
258    inline void renameDestRegs(DynInstPtr &inst, ThreadID tid);
259
260    /** Calculates the number of free ROB entries for a specific thread. */
261    inline int calcFreeROBEntries(ThreadID tid);
262
263    /** Calculates the number of free IQ entries for a specific thread. */
264    inline int calcFreeIQEntries(ThreadID tid);
265
266    /** Calculates the number of free LQ entries for a specific thread. */
267    inline int calcFreeLQEntries(ThreadID tid);
268
269    /** Calculates the number of free SQ entries for a specific thread. */
270    inline int calcFreeSQEntries(ThreadID tid);
271
272    /** Returns the number of valid instructions coming from decode. */
273    unsigned validInsts();
274
275    /** Reads signals telling rename to block/unblock. */
276    void readStallSignals(ThreadID tid);
277
278    /** Checks if any stages are telling rename to block. */
279    bool checkStall(ThreadID tid);
280
281    /** Gets the number of free entries for a specific thread. */
282    void readFreeEntries(ThreadID tid);
283
284    /** Checks the signals and updates the status. */
285    bool checkSignalsAndUpdate(ThreadID tid);
286
287    /** Either serializes on the next instruction available in the InstQueue,
288     * or records that it must serialize on the next instruction to enter
289     * rename.
290     * @param inst_list The list of younger, unprocessed instructions for the
291     * thread that has the serializeAfter instruction.
292     * @param tid The thread id.
293     */
294    void serializeAfter(InstQueue &inst_list, ThreadID tid);
295
296    /** Holds the information for each destination register rename. It holds
297     * the instruction's sequence number, the arch register, the old physical
298     * register for that arch. register, and the new physical register.
299     */
300    struct RenameHistory {
301        RenameHistory(InstSeqNum _instSeqNum, const RegId& _archReg,
302                      PhysRegIdPtr _newPhysReg,
303                      PhysRegIdPtr _prevPhysReg)
304            : instSeqNum(_instSeqNum), archReg(_archReg),
305              newPhysReg(_newPhysReg), prevPhysReg(_prevPhysReg)
306        {
307        }
308
309        /** The sequence number of the instruction that renamed. */
310        InstSeqNum instSeqNum;
311        /** The architectural register index that was renamed. */
312        RegId archReg;
313        /** The new physical register that the arch. register is renamed to. */
314        PhysRegIdPtr newPhysReg;
315        /** The old physical register that the arch. register was renamed to.
316         */
317        PhysRegIdPtr prevPhysReg;
318    };
319
320    /** A per-thread list of all destination register renames, used to either
321     * undo rename mappings or free old physical registers.
322     */
323    std::list<RenameHistory> historyBuffer[Impl::MaxThreads];
324
325    /** Pointer to CPU. */
326    O3CPU *cpu;
327
328    /** Pointer to main time buffer used for backwards communication. */
329    TimeBuffer<TimeStruct> *timeBuffer;
330
331    /** Wire to get IEW's output from backwards time buffer. */
332    typename TimeBuffer<TimeStruct>::wire fromIEW;
333
334    /** Wire to get commit's output from backwards time buffer. */
335    typename TimeBuffer<TimeStruct>::wire fromCommit;
336
337    /** Wire to write infromation heading to previous stages. */
338    typename TimeBuffer<TimeStruct>::wire toDecode;
339
340    /** Rename instruction queue. */
341    TimeBuffer<RenameStruct> *renameQueue;
342
343    /** Wire to write any information heading to IEW. */
344    typename TimeBuffer<RenameStruct>::wire toIEW;
345
346    /** Decode instruction queue interface. */
347    TimeBuffer<DecodeStruct> *decodeQueue;
348
349    /** Wire to get decode's output from decode queue. */
350    typename TimeBuffer<DecodeStruct>::wire fromDecode;
351
352    /** Queue of all instructions coming from decode this cycle. */
353    InstQueue insts[Impl::MaxThreads];
354
355    /** Skid buffer between rename and decode. */
356    InstQueue skidBuffer[Impl::MaxThreads];
357
358    /** Rename map interface. */
359    RenameMap *renameMap[Impl::MaxThreads];
360
361    /** Free list interface. */
362    FreeList *freeList;
363
364    /** Pointer to the list of active threads. */
365    std::list<ThreadID> *activeThreads;
366
367    /** Pointer to the scoreboard. */
368    Scoreboard *scoreboard;
369
370    /** Count of instructions in progress that have been sent off to the IQ
371     * and ROB, but are not yet included in their occupancy counts.
372     */
373    int instsInProgress[Impl::MaxThreads];
374
375    /** Count of Load instructions in progress that have been sent off to the IQ
376     * and ROB, but are not yet included in their occupancy counts.
377     */
378    int loadsInProgress[Impl::MaxThreads];
379
380    /** Count of Store instructions in progress that have been sent off to the IQ
381     * and ROB, but are not yet included in their occupancy counts.
382     */
383    int storesInProgress[Impl::MaxThreads];
384
385    /** Variable that tracks if decode has written to the time buffer this
386     * cycle. Used to tell CPU if there is activity this cycle.
387     */
388    bool wroteToTimeBuffer;
389
390    /** Structures whose free entries impact the amount of instructions that
391     * can be renamed.
392     */
393    struct FreeEntries {
394        unsigned iqEntries;
395        unsigned robEntries;
396        unsigned lqEntries;
397        unsigned sqEntries;
398    };
399
400    /** Per-thread tracking of the number of free entries of back-end
401     * structures.
402     */
403    FreeEntries freeEntries[Impl::MaxThreads];
404
405    /** Records if the ROB is empty. In SMT mode the ROB may be dynamically
406     * partitioned between threads, so the ROB must tell rename when it is
407     * empty.
408     */
409    bool emptyROB[Impl::MaxThreads];
410
411    /** Source of possible stalls. */
412    struct Stalls {
413        bool iew;
414        bool commit;
415    };
416
417    /** Tracks which stages are telling decode to stall. */
418    Stalls stalls[Impl::MaxThreads];
419
420    /** The serialize instruction that rename has stalled on. */
421    DynInstPtr serializeInst[Impl::MaxThreads];
422
423    /** Records if rename needs to serialize on the next instruction for any
424     * thread.
425     */
426    bool serializeOnNextInst[Impl::MaxThreads];
427
428    /** Delay between iew and rename, in ticks. */
429    int iewToRenameDelay;
430
431    /** Delay between decode and rename, in ticks. */
432    int decodeToRenameDelay;
433
434    /** Delay between commit and rename, in ticks. */
435    unsigned commitToRenameDelay;
436
437    /** Rename width, in instructions. */
438    unsigned renameWidth;
439
440    /** Commit width, in instructions.  Used so rename knows how many
441     *  instructions might have freed registers in the previous cycle.
442     */
443    unsigned commitWidth;
444
445    /** The index of the instruction in the time buffer to IEW that rename is
446     * currently using.
447     */
448    unsigned toIEWIndex;
449
450    /** Whether or not rename needs to block this cycle. */
451    bool blockThisCycle;
452
453    /** Whether or not rename needs to resume a serialize instruction
454     * after squashing. */
455    bool resumeSerialize;
456
457    /** Whether or not rename needs to resume clearing out the skidbuffer
458     * after squashing. */
459    bool resumeUnblocking;
460
461    /** The number of threads active in rename. */
462    ThreadID numThreads;
463
464    /** The maximum skid buffer size. */
465    unsigned skidBufferMax;
466
467    PhysRegIndex maxPhysicalRegs;
468
469    /** Enum to record the source of a structure full stall.  Can come from
470     * either ROB, IQ, LSQ, and it is priortized in that order.
471     */
472    enum FullSource {
473        ROB,
474        IQ,
475        LQ,
476        SQ,
477        NONE
478    };
479
480    /** Function used to increment the stat that corresponds to the source of
481     * the stall.
482     */
483    inline void incrFullStat(const FullSource &source);
484
485    /** Stat for total number of cycles spent squashing. */
486    Stats::Scalar renameSquashCycles;
487    /** Stat for total number of cycles spent idle. */
488    Stats::Scalar renameIdleCycles;
489    /** Stat for total number of cycles spent blocking. */
490    Stats::Scalar renameBlockCycles;
491    /** Stat for total number of cycles spent stalling for a serializing inst. */
492    Stats::Scalar renameSerializeStallCycles;
493    /** Stat for total number of cycles spent running normally. */
494    Stats::Scalar renameRunCycles;
495    /** Stat for total number of cycles spent unblocking. */
496    Stats::Scalar renameUnblockCycles;
497    /** Stat for total number of renamed instructions. */
498    Stats::Scalar renameRenamedInsts;
499    /** Stat for total number of squashed instructions that rename discards. */
500    Stats::Scalar renameSquashedInsts;
501    /** Stat for total number of times that the ROB starts a stall in rename. */
502    Stats::Scalar renameROBFullEvents;
503    /** Stat for total number of times that the IQ starts a stall in rename. */
504    Stats::Scalar renameIQFullEvents;
505    /** Stat for total number of times that the LQ starts a stall in rename. */
506    Stats::Scalar renameLQFullEvents;
507    /** Stat for total number of times that the SQ starts a stall in rename. */
508    Stats::Scalar renameSQFullEvents;
509    /** Stat for total number of times that rename runs out of free registers
510     * to use to rename. */
511    Stats::Scalar renameFullRegistersEvents;
512    /** Stat for total number of renamed destination registers. */
513    Stats::Scalar renameRenamedOperands;
514    /** Stat for total number of source register rename lookups. */
515    Stats::Scalar renameRenameLookups;
516    Stats::Scalar intRenameLookups;
517    Stats::Scalar fpRenameLookups;
518    /** Stat for total number of committed renaming mappings. */
519    Stats::Scalar renameCommittedMaps;
520    /** Stat for total number of mappings that were undone due to a squash. */
521    Stats::Scalar renameUndoneMaps;
522    /** Number of serialize instructions handled. */
523    Stats::Scalar renamedSerializing;
524    /** Number of instructions marked as temporarily serializing. */
525    Stats::Scalar renamedTempSerializing;
526    /** Number of instructions inserted into skid buffers. */
527    Stats::Scalar renameSkidInsts;
528};
529
530#endif // __CPU_O3_RENAME_HH__
531