dram_ctrl.hh revision 10207 
1/*
2 * Copyright (c) 2012-2014 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) 2013 Amin Farmahini-Farahani
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: Andreas Hansson
41 *          Ani Udipi
42 *          Neha Agarwal
43 */
44
45/**
46 * @file
47 * DRAMCtrl declaration
48 */
49
50#ifndef __MEM_DRAM_CTRL_HH__
51#define __MEM_DRAM_CTRL_HH__
52
53#include <deque>
54
55#include "base/statistics.hh"
56#include "enums/AddrMap.hh"
57#include "enums/MemSched.hh"
58#include "enums/PageManage.hh"
59#include "mem/abstract_mem.hh"
60#include "mem/qport.hh"
61#include "params/DRAMCtrl.hh"
62#include "sim/eventq.hh"
63
64/**
65 * The DRAM controller is a basic single-channel memory controller
66 * aiming to mimic a high-level DRAM controller and the most important
67 * timing constraints associated with the DRAM. The focus is really on
68 * modelling the impact on the system rather than the DRAM itself,
69 * hence the focus is on the controller model and not on the
70 * memory. By adhering to the correct timing constraints, ultimately
71 * there is no need for a memory model in addition to the controller
72 * model.
73 *
74 * As a basic design principle, this controller is not cycle callable,
75 * but instead uses events to decide when new decisions can be made,
76 * when resources become available, when things are to be considered
77 * done, and when to send things back. Through these simple
78 * principles, we achieve a performant model that is not
79 * cycle-accurate, but enables us to evaluate the system impact of a
80 * wide range of memory technologies, and also collect statistics
81 * about the use of the memory.
82 */
83class DRAMCtrl : public AbstractMemory
84{
85
86  private:
87
88    // For now, make use of a queued slave port to avoid dealing with
89    // flow control for the responses being sent back
90    class MemoryPort : public QueuedSlavePort
91    {
92
93        SlavePacketQueue queue;
94        DRAMCtrl& memory;
95
96      public:
97
98        MemoryPort(const std::string& name, DRAMCtrl& _memory);
99
100      protected:
101
102        Tick recvAtomic(PacketPtr pkt);
103
104        void recvFunctional(PacketPtr pkt);
105
106        bool recvTimingReq(PacketPtr);
107
108        virtual AddrRangeList getAddrRanges() const;
109
110    };
111
112    /**
113     * Our incoming port, for a multi-ported controller add a crossbar
114     * in front of it
115     */
116    MemoryPort port;
117
118    /**
119     * Remember if we have to retry a request when available.
120     */
121    bool retryRdReq;
122    bool retryWrReq;
123
124    /**
125     * Remember that a row buffer hit occured
126     */
127    bool rowHitFlag;
128
129    /**
130     * Bus state used to control the read/write switching and drive
131     * the scheduling of the next request.
132     */
133    enum BusState {
134        READ = 0,
135        READ_TO_WRITE,
136        WRITE,
137        WRITE_TO_READ
138    };
139
140    BusState busState;
141
142    /** List to keep track of activate ticks */
143    std::vector<std::deque<Tick>> actTicks;
144
145    /**
146     * A basic class to track the bank state indirectly via times
147     * "freeAt" and "tRASDoneAt" and what page is currently open. The
148     * bank also keeps track of how many bytes have been accessed in
149     * the open row since it was opened.
150     */
151    class Bank
152    {
153
154      public:
155
156        static const uint32_t NO_ROW = -1;
157
158        uint32_t openRow;
159
160        Tick freeAt;
161        Tick tRASDoneAt;
162        Tick actAllowedAt;
163
164        uint32_t rowAccesses;
165        uint32_t bytesAccessed;
166
167        Bank() :
168            openRow(NO_ROW), freeAt(0), tRASDoneAt(0), actAllowedAt(0),
169            rowAccesses(0), bytesAccessed(0)
170        { }
171    };
172
173    /**
174     * A burst helper helps organize and manage a packet that is larger than
175     * the DRAM burst size. A system packet that is larger than the burst size
176     * is split into multiple DRAM packets and all those DRAM packets point to
177     * a single burst helper such that we know when the whole packet is served.
178     */
179    class BurstHelper {
180
181      public:
182
183        /** Number of DRAM bursts requred for a system packet **/
184        const unsigned int burstCount;
185
186        /** Number of DRAM bursts serviced so far for a system packet **/
187        unsigned int burstsServiced;
188
189        BurstHelper(unsigned int _burstCount)
190            : burstCount(_burstCount), burstsServiced(0)
191            { }
192    };
193
194    /**
195     * A DRAM packet stores packets along with the timestamp of when
196     * the packet entered the queue, and also the decoded address.
197     */
198    class DRAMPacket {
199
200      public:
201
202        /** When did request enter the controller */
203        const Tick entryTime;
204
205        /** When will request leave the controller */
206        Tick readyTime;
207
208        /** This comes from the outside world */
209        const PacketPtr pkt;
210
211        const bool isRead;
212
213        /** Will be populated by address decoder */
214        const uint8_t rank;
215        const uint8_t bank;
216        const uint16_t row;
217
218        /**
219         * Bank id is calculated considering banks in all the ranks
220         * eg: 2 ranks each with 8 banks, then bankId = 0 --> rank0, bank0 and
221         * bankId = 8 --> rank1, bank0
222         */
223        const uint16_t bankId;
224
225        /**
226         * The starting address of the DRAM packet.
227         * This address could be unaligned to burst size boundaries. The
228         * reason is to keep the address offset so we can accurately check
229         * incoming read packets with packets in the write queue.
230         */
231        Addr addr;
232
233        /**
234         * The size of this dram packet in bytes
235         * It is always equal or smaller than DRAM burst size
236         */
237        unsigned int size;
238
239        /**
240         * A pointer to the BurstHelper if this DRAMPacket is a split packet
241         * If not a split packet (common case), this is set to NULL
242         */
243        BurstHelper* burstHelper;
244        Bank& bankRef;
245
246        DRAMPacket(PacketPtr _pkt, bool is_read, uint8_t _rank, uint8_t _bank,
247                   uint16_t _row, uint16_t bank_id, Addr _addr,
248                   unsigned int _size, Bank& bank_ref)
249            : entryTime(curTick()), readyTime(curTick()),
250              pkt(_pkt), isRead(is_read), rank(_rank), bank(_bank), row(_row),
251              bankId(bank_id), addr(_addr), size(_size), burstHelper(NULL),
252              bankRef(bank_ref)
253        { }
254
255    };
256
257    /**
258     * Bunch of things requires to setup "events" in gem5
259     * When event "respondEvent" occurs for example, the method
260     * processRespondEvent is called; no parameters are allowed
261     * in these methods
262     */
263    void processRespondEvent();
264    EventWrapper<DRAMCtrl, &DRAMCtrl::processRespondEvent> respondEvent;
265
266    void processRefreshEvent();
267    EventWrapper<DRAMCtrl, &DRAMCtrl::processRefreshEvent> refreshEvent;
268
269    void processNextReqEvent();
270    EventWrapper<DRAMCtrl,&DRAMCtrl::processNextReqEvent> nextReqEvent;
271
272
273    /**
274     * Check if the read queue has room for more entries
275     *
276     * @param pktCount The number of entries needed in the read queue
277     * @return true if read queue is full, false otherwise
278     */
279    bool readQueueFull(unsigned int pktCount) const;
280
281    /**
282     * Check if the write queue has room for more entries
283     *
284     * @param pktCount The number of entries needed in the write queue
285     * @return true if write queue is full, false otherwise
286     */
287    bool writeQueueFull(unsigned int pktCount) const;
288
289    /**
290     * When a new read comes in, first check if the write q has a
291     * pending request to the same address.\ If not, decode the
292     * address to populate rank/bank/row, create one or mutliple
293     * "dram_pkt", and push them to the back of the read queue.\
294     * If this is the only
295     * read request in the system, schedule an event to start
296     * servicing it.
297     *
298     * @param pkt The request packet from the outside world
299     * @param pktCount The number of DRAM bursts the pkt
300     * translate to. If pkt size is larger then one full burst,
301     * then pktCount is greater than one.
302     */
303    void addToReadQueue(PacketPtr pkt, unsigned int pktCount);
304
305    /**
306     * Decode the incoming pkt, create a dram_pkt and push to the
307     * back of the write queue. \If the write q length is more than
308     * the threshold specified by the user, ie the queue is beginning
309     * to get full, stop reads, and start draining writes.
310     *
311     * @param pkt The request packet from the outside world
312     * @param pktCount The number of DRAM bursts the pkt
313     * translate to. If pkt size is larger then one full burst,
314     * then pktCount is greater than one.
315     */
316    void addToWriteQueue(PacketPtr pkt, unsigned int pktCount);
317
318    /**
319     * Actually do the DRAM access - figure out the latency it
320     * will take to service the req based on bank state, channel state etc
321     * and then update those states to account for this request.\ Based
322     * on this, update the packet's "readyTime" and move it to the
323     * response q from where it will eventually go back to the outside
324     * world.
325     *
326     * @param pkt The DRAM packet created from the outside world pkt
327     */
328    void doDRAMAccess(DRAMPacket* dram_pkt);
329
330    /**
331     * When a packet reaches its "readyTime" in the response Q,
332     * use the "access()" method in AbstractMemory to actually
333     * create the response packet, and send it back to the outside
334     * world requestor.
335     *
336     * @param pkt The packet from the outside world
337     * @param static_latency Static latency to add before sending the packet
338     */
339    void accessAndRespond(PacketPtr pkt, Tick static_latency);
340
341    /**
342     * Address decoder to figure out physical mapping onto ranks,
343     * banks, and rows. This function is called multiple times on the same
344     * system packet if the pakcet is larger than burst of the memory. The
345     * dramPktAddr is used for the offset within the packet.
346     *
347     * @param pkt The packet from the outside world
348     * @param dramPktAddr The starting address of the DRAM packet
349     * @param size The size of the DRAM packet in bytes
350     * @param isRead Is the request for a read or a write to DRAM
351     * @return A DRAMPacket pointer with the decoded information
352     */
353    DRAMPacket* decodeAddr(PacketPtr pkt, Addr dramPktAddr, unsigned int size,
354                           bool isRead);
355
356    /**
357     * The memory schduler/arbiter - picks which request needs to
358     * go next, based on the specified policy such as FCFS or FR-FCFS
359     * and moves it to the head of the queue.
360     */
361    void chooseNext(std::deque<DRAMPacket*>& queue);
362
363    /**
364     *Looks at the state of the banks, channels, row buffer hits etc
365     * to estimate how long a request will take to complete.
366     *
367     * @param dram_pkt The request for which we want to estimate latency
368     * @param inTime The tick at which you want to probe the memory
369     *
370     * @return A pair of ticks, one indicating how many ticks *after*
371     *         inTime the request require, and the other indicating how
372     *         much of that was just the bank access time, ignoring the
373     *         ticks spent simply waiting for resources to become free
374     */
375    std::pair<Tick, Tick> estimateLatency(DRAMPacket* dram_pkt, Tick inTime);
376
377    /**
378     * Move the request at the head of the read queue to the response
379     * queue, sorting by readyTime.\ If it is the only packet in the
380     * response queue, schedule a respond event to send it back to the
381     * outside world
382     */
383    void moveToRespQ();
384
385    /**
386     * For FR-FCFS policy reorder the read/write queue depending on row buffer
387     * hits and earliest banks available in DRAM
388     */
389    void reorderQueue(std::deque<DRAMPacket*>& queue);
390
391    /**
392     * Find which are the earliest available banks for the enqueued
393     * requests. Assumes maximum of 64 banks per DIMM
394     *
395     * @param Queued requests to consider
396     * @return One-hot encoded mask of bank indices
397     */
398    uint64_t minBankFreeAt(const std::deque<DRAMPacket*>& queue) const;
399
400    /**
401     * Keep track of when row activations happen, in order to enforce
402     * the maximum number of activations in the activation window. The
403     * method updates the time that the banks become available based
404     * on the current limits.
405     */
406    void recordActivate(Tick act_tick, uint8_t rank, uint8_t bank,
407                        uint16_t row);
408
409    /**
410     * Precharge a given bank and also update when the precharge is
411     * done. This will also deal with any stats related to the
412     * accesses to the open page.
413     *
414     * @param bank The bank to precharge
415     * @param free_at Time when the precharge is done
416     */
417    void prechargeBank(Bank& bank, Tick free_at);
418
419    void printParams() const;
420
421    /**
422     * Used for debugging to observe the contents of the queues.
423     */
424    void printQs() const;
425
426    /**
427     * The controller's main read and write queues
428     */
429    std::deque<DRAMPacket*> readQueue;
430    std::deque<DRAMPacket*> writeQueue;
431
432    /**
433     * Response queue where read packets wait after we're done working
434     * with them, but it's not time to send the response yet. The
435     * responses are stored seperately mostly to keep the code clean
436     * and help with events scheduling. For all logical purposes such
437     * as sizing the read queue, this and the main read queue need to
438     * be added together.
439     */
440    std::deque<DRAMPacket*> respQueue;
441
442    /**
443     * If we need to drain, keep the drain manager around until we're
444     * done here.
445     */
446    DrainManager *drainManager;
447
448    /**
449     * Multi-dimensional vector of banks, first dimension is ranks,
450     * second is bank
451     */
452    std::vector<std::vector<Bank> > banks;
453
454    /**
455     * The following are basic design parameters of the memory
456     * controller, and are initialized based on parameter values.
457     * The rowsPerBank is determined based on the capacity, number of
458     * ranks and banks, the burst size, and the row buffer size.
459     */
460    const uint32_t deviceBusWidth;
461    const uint32_t burstLength;
462    const uint32_t deviceRowBufferSize;
463    const uint32_t devicesPerRank;
464    const uint32_t burstSize;
465    const uint32_t rowBufferSize;
466    const uint32_t columnsPerRowBuffer;
467    const uint32_t ranksPerChannel;
468    const uint32_t banksPerRank;
469    const uint32_t channels;
470    uint32_t rowsPerBank;
471    const uint32_t readBufferSize;
472    const uint32_t writeBufferSize;
473    const uint32_t writeHighThreshold;
474    const uint32_t writeLowThreshold;
475    const uint32_t minWritesPerSwitch;
476    uint32_t writesThisTime;
477    uint32_t readsThisTime;
478
479    /**
480     * Basic memory timing parameters initialized based on parameter
481     * values.
482     */
483    const Tick tWTR;
484    const Tick tRTW;
485    const Tick tBURST;
486    const Tick tRCD;
487    const Tick tCL;
488    const Tick tRP;
489    const Tick tRAS;
490    const Tick tRFC;
491    const Tick tREFI;
492    const Tick tRRD;
493    const Tick tXAW;
494    const uint32_t activationLimit;
495
496    /**
497     * Memory controller configuration initialized based on parameter
498     * values.
499     */
500    Enums::MemSched memSchedPolicy;
501    Enums::AddrMap addrMapping;
502    Enums::PageManage pageMgmt;
503
504    /**
505     * Max column accesses (read and write) per row, before forefully
506     * closing it.
507     */
508    const uint32_t maxAccessesPerRow;
509
510    /**
511     * Pipeline latency of the controller frontend. The frontend
512     * contribution is added to writes (that complete when they are in
513     * the write buffer) and reads that are serviced the write buffer.
514     */
515    const Tick frontendLatency;
516
517    /**
518     * Pipeline latency of the backend and PHY. Along with the
519     * frontend contribution, this latency is added to reads serviced
520     * by the DRAM.
521     */
522    const Tick backendLatency;
523
524    /**
525     * Till when has the main data bus been spoken for already?
526     */
527    Tick busBusyUntil;
528
529    /**
530     * Keep track of when a refresh is due.
531     */
532    Tick refreshDueAt;
533
534    /**
535     * The refresh state is used to control the progress of the
536     * refresh scheduling. When normal operation is in progress the
537     * refresh state is idle. From there, it progresses to the refresh
538     * drain state once tREFI has passed. The refresh drain state
539     * captures the DRAM row active state, as it will stay there until
540     * all ongoing accesses complete. Thereafter all banks are
541     * precharged, and lastly, the DRAM is refreshed.
542     */
543    enum RefreshState {
544        REF_IDLE = 0,
545        REF_DRAIN,
546        REF_PRE,
547        REF_RUN
548    };
549
550    RefreshState refreshState;
551
552    Tick prevArrival;
553
554    /**
555     * The soonest you have to start thinking about the next request
556     * is the longest access time that can occur before
557     * busBusyUntil. Assuming you need to precharge, open a new row,
558     * and access, it is tRP + tRCD + tCL.
559     */
560    Tick nextReqTime;
561
562    // All statistics that the model needs to capture
563    Stats::Scalar readReqs;
564    Stats::Scalar writeReqs;
565    Stats::Scalar readBursts;
566    Stats::Scalar writeBursts;
567    Stats::Scalar bytesReadDRAM;
568    Stats::Scalar bytesReadWrQ;
569    Stats::Scalar bytesWritten;
570    Stats::Scalar bytesReadSys;
571    Stats::Scalar bytesWrittenSys;
572    Stats::Scalar servicedByWrQ;
573    Stats::Scalar mergedWrBursts;
574    Stats::Scalar neitherReadNorWrite;
575    Stats::Vector perBankRdBursts;
576    Stats::Vector perBankWrBursts;
577    Stats::Scalar numRdRetry;
578    Stats::Scalar numWrRetry;
579    Stats::Scalar totGap;
580    Stats::Vector readPktSize;
581    Stats::Vector writePktSize;
582    Stats::Vector rdQLenPdf;
583    Stats::Vector wrQLenPdf;
584    Stats::Histogram bytesPerActivate;
585    Stats::Histogram rdPerTurnAround;
586    Stats::Histogram wrPerTurnAround;
587
588    // Latencies summed over all requests
589    Stats::Scalar totQLat;
590    Stats::Scalar totMemAccLat;
591    Stats::Scalar totBusLat;
592    Stats::Scalar totBankLat;
593
594    // Average latencies per request
595    Stats::Formula avgQLat;
596    Stats::Formula avgBankLat;
597    Stats::Formula avgBusLat;
598    Stats::Formula avgMemAccLat;
599
600    // Average bandwidth
601    Stats::Formula avgRdBW;
602    Stats::Formula avgWrBW;
603    Stats::Formula avgRdBWSys;
604    Stats::Formula avgWrBWSys;
605    Stats::Formula peakBW;
606    Stats::Formula busUtil;
607    Stats::Formula busUtilRead;
608    Stats::Formula busUtilWrite;
609
610    // Average queue lengths
611    Stats::Average avgRdQLen;
612    Stats::Average avgWrQLen;
613
614    // Row hit count and rate
615    Stats::Scalar readRowHits;
616    Stats::Scalar writeRowHits;
617    Stats::Formula readRowHitRate;
618    Stats::Formula writeRowHitRate;
619    Stats::Formula avgGap;
620
621    // DRAM Power Calculation
622    Stats::Formula pageHitRate;
623    Stats::Formula prechargeAllPercent;
624    Stats::Scalar prechargeAllTime;
625
626    // To track number of cycles the DRAM is idle, i.e. all the banks
627    // are precharged
628    Tick idleStartTick;
629
630    // To track number of banks which are currently active
631    unsigned int numBanksActive;
632
633    /** @todo this is a temporary workaround until the 4-phase code is
634     * committed. upstream caches needs this packet until true is returned, so
635     * hold onto it for deletion until a subsequent call
636     */
637    std::vector<PacketPtr> pendingDelete;
638
639  public:
640
641    void regStats();
642
643    DRAMCtrl(const DRAMCtrlParams* p);
644
645    unsigned int drain(DrainManager* dm);
646
647    virtual BaseSlavePort& getSlavePort(const std::string& if_name,
648                                        PortID idx = InvalidPortID);
649
650    virtual void init();
651    virtual void startup();
652
653  protected:
654
655    Tick recvAtomic(PacketPtr pkt);
656    void recvFunctional(PacketPtr pkt);
657    bool recvTimingReq(PacketPtr pkt);
658
659};
660
661#endif //__MEM_DRAM_CTRL_HH__
662