gem5/src/cpu/o3/rob.hh

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 * All rights reserved.
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 * met: redistributions of source code must retain the above copyright
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#ifndef __CPU_O3_ROB_HH__
#define __CPU_O3_ROB_HH__

#include <string>
#include <utility>
#include <vector>

#include "base/statistics.hh"
#include "base/types.hh"
#include "config/the_isa.hh"
#include "cpu/inst_seq.hh"
#include "cpu/o3/dyn_inst_ptr.hh"
#include "cpu/o3/limits.hh"
#include "cpu/reg_class.hh"
#include "enums/SMTQueuePolicy.hh"

namespace gem5
{

struct O3CPUParams;

namespace o3
{

class CPU;

struct DerivO3CPUParams;

/**
 * ROB class.  The ROB is largely what drives squashing.
 */
class ROB
{
  public:
    typedef std::pair<RegIndex, RegIndex> UnmapInfo;
    typedef typename std::list<DynInstPtr>::iterator InstIt;

    /** Possible ROB statuses. */
    enum Status
    {
        Running,
        Idle,
        ROBSquashing
    };

  private:
    /** Per-thread ROB status. */
    Status robStatus[MaxThreads];

    /** ROB resource sharing policy for SMT mode. */
    SMTQueuePolicy robPolicy;

  public:
    /** ROB constructor.
     *  @param _cpu   The cpu object pointer.
     *  @param params The cpu params including several ROB-specific parameters.
     */
    ROB(CPU *_cpu, const O3CPUParams &params);

    std::string name() const;

    /** Sets pointer to the list of active threads.
     *  @param at_ptr Pointer to the list of active threads.
     */
    void setActiveThreads(std::list<ThreadID> *at_ptr);

    /** Perform sanity checks after a drain. */
    void drainSanityCheck() const;

    /** Takes over another CPU's thread. */
    void takeOverFrom();

    /** Function to insert an instruction into the ROB. Note that whatever
     *  calls this function must ensure that there is enough space within the
     *  ROB for the new instruction.
     *  @param inst The instruction being inserted into the ROB.
     */
    void insertInst(const DynInstPtr &inst);

    /** Returns pointer to the head instruction within the ROB.  There is
     *  no guarantee as to the return value if the ROB is empty.
     *  @retval Pointer to the DynInst that is at the head of the ROB.
     */
//    DynInstPtr readHeadInst();

    /** Returns a pointer to the head instruction of a specific thread within
     *  the ROB.
     *  @return Pointer to the DynInst that is at the head of the ROB.
     */
    const DynInstPtr &readHeadInst(ThreadID tid);

    /** Returns a pointer to the instruction with the given sequence if it is
     *  in the ROB.
     */
    DynInstPtr findInst(ThreadID tid, InstSeqNum squash_inst);

    /** Returns pointer to the tail instruction within the ROB.  There is
     *  no guarantee as to the return value if the ROB is empty.
     *  @retval Pointer to the DynInst that is at the tail of the ROB.
     */
//    DynInstPtr readTailInst();

    /** Returns a pointer to the tail instruction of a specific thread within
     *  the ROB.
     *  @return Pointer to the DynInst that is at the tail of the ROB.
     */
    DynInstPtr readTailInst(ThreadID tid);

    /** Retires the head instruction, removing it from the ROB. */
//    void retireHead();

    /** Retires the head instruction of a specific thread, removing it from the
     *  ROB.
     */
    void retireHead(ThreadID tid);

    /** Is the oldest instruction across all threads ready. */
//    bool isHeadReady();

    /** Is the oldest instruction across a particular thread ready. */
    bool isHeadReady(ThreadID tid);

    /** Is there any commitable head instruction across all threads ready. */
    bool canCommit();

    /** Re-adjust ROB partitioning. */
    void resetEntries();

    /** Number of entries needed For 'num_threads' amount of threads. */
    int entryAmount(ThreadID num_threads);

    /** Returns the number of total free entries in the ROB. */
    unsigned numFreeEntries();

    /** Returns the number of free entries in a specific ROB paritition. */
    unsigned numFreeEntries(ThreadID tid);

    /** Returns the maximum number of entries for a specific thread. */
    unsigned getMaxEntries(ThreadID tid)
    { return maxEntries[tid]; }

    /** Returns the number of entries being used by a specific thread. */
    unsigned getThreadEntries(ThreadID tid)
    { return threadEntries[tid]; }

    /** Returns if the ROB is full. */
    bool isFull()
    { return numInstsInROB == numEntries; }

    /** Returns if a specific thread's partition is full. */
    bool isFull(ThreadID tid)
    { return threadEntries[tid] == numEntries; }

    /** Returns if the ROB is empty. */
    bool isEmpty() const
    { return numInstsInROB == 0; }

    /** Returns if a specific thread's partition is empty. */
    bool isEmpty(ThreadID tid) const
    { return threadEntries[tid] == 0; }

    /** Executes the squash, marking squashed instructions. */
    void doSquash(ThreadID tid);

    /** Squashes all instructions younger than the given sequence number for
     *  the specific thread.
     */
    void squash(InstSeqNum squash_num, ThreadID tid);

    /** Updates the head instruction with the new oldest instruction. */
    void updateHead();

    /** Updates the tail instruction with the new youngest instruction. */
    void updateTail();

    /** Reads the PC of the oldest head instruction. */
//    uint64_t readHeadPC();

    /** Reads the PC of the head instruction of a specific thread. */
//    uint64_t readHeadPC(ThreadID tid);

    /** Reads the next PC of the oldest head instruction. */
//    uint64_t readHeadNextPC();

    /** Reads the next PC of the head instruction of a specific thread. */
//    uint64_t readHeadNextPC(ThreadID tid);

    /** Reads the sequence number of the oldest head instruction. */
//    InstSeqNum readHeadSeqNum();

    /** Reads the sequence number of the head instruction of a specific thread.
     */
//    InstSeqNum readHeadSeqNum(ThreadID tid);

    /** Reads the PC of the youngest tail instruction. */
//    uint64_t readTailPC();

    /** Reads the PC of the tail instruction of a specific thread. */
//    uint64_t readTailPC(ThreadID tid);

    /** Reads the sequence number of the youngest tail instruction. */
//    InstSeqNum readTailSeqNum();

    /** Reads the sequence number of tail instruction of a specific thread. */
//    InstSeqNum readTailSeqNum(ThreadID tid);

    /** Checks if the ROB is still in the process of squashing instructions.
     *  @retval Whether or not the ROB is done squashing.
     */
    bool isDoneSquashing(ThreadID tid) const
    { return doneSquashing[tid]; }

    /** Checks if the ROB is still in the process of squashing instructions for
     *  any thread.
     */
    bool isDoneSquashing();

    /** This is more of a debugging function than anything.  Use
     *  numInstsInROB to get the instructions in the ROB unless you are
     *  double checking that variable.
     */
    int countInsts();

    /** This is more of a debugging function than anything.  Use
     *  threadEntries to get the instructions in the ROB unless you are
     *  double checking that variable.
     */
    size_t countInsts(ThreadID tid);

  private:
    /** Reset the ROB state */
    void resetState();

    /** Pointer to the CPU. */
    CPU *cpu;

    /** Active Threads in CPU */
    std::list<ThreadID> *activeThreads;

    /** Number of instructions in the ROB. */
    unsigned numEntries;

    /** Entries Per Thread */
    unsigned threadEntries[MaxThreads];

    /** Max Insts a Thread Can Have in the ROB */
    unsigned maxEntries[MaxThreads];

    /** ROB List of Instructions */
    std::list<DynInstPtr> instList[MaxThreads];

    /** Number of instructions that can be squashed in a single cycle. */
    unsigned squashWidth;

  public:
    /** Iterator pointing to the instruction which is the last instruction
     *  in the ROB.  This may at times be invalid (ie when the ROB is empty),
     *  however it should never be incorrect.
     */
    InstIt tail;

    /** Iterator pointing to the instruction which is the first instruction in
     *  in the ROB*/
    InstIt head;

  private:
    /** Iterator used for walking through the list of instructions when
     *  squashing.  Used so that there is persistent state between cycles;
     *  when squashing, the instructions are marked as squashed but not
     *  immediately removed, meaning the tail iterator remains the same before
     *  and after a squash.
     *  This will always be set to cpu->instList.end() if it is invalid.
     */
    InstIt squashIt[MaxThreads];

  public:
    /** Number of instructions in the ROB. */
    int numInstsInROB;

    /** Dummy instruction returned if there are no insts left. */
    DynInstPtr dummyInst;

  private:
    /** The sequence number of the squashed instruction. */
    InstSeqNum squashedSeqNum[MaxThreads];

    /** Is the ROB done squashing. */
    bool doneSquashing[MaxThreads];

    /** Number of active threads. */
    ThreadID numThreads;


    struct ROBStats : public statistics::Group
    {
        ROBStats(statistics::Group *parent);

        // The number of rob_reads
        statistics::Scalar reads;
        // The number of rob_writes
        statistics::Scalar writes;
    } stats;
};

} // namespace o3
} // namespace gem5

#endif //__CPU_O3_ROB_HH__