xref: /gem5/src/cpu/o3/lsq_unit.hh

/*
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#ifndef __CPU_O3_LSQ_UNIT_HH__
#define __CPU_O3_LSQ_UNIT_HH__

#include <map>
#include <queue>
#include <algorithm>

#include "config/full_system.hh"
#include "base/hashmap.hh"
#include "cpu/inst_seq.hh"
#include "mem/mem_interface.hh"
//#include "mem/page_table.hh"
#include "sim/sim_object.hh"
#include "arch/faults.hh"

/**
 * Class that implements the actual LQ and SQ for each specific thread.
 * Both are circular queues; load entries are freed upon committing, while
 * store entries are freed once they writeback. The LSQUnit tracks if there
 * are memory ordering violations, and also detects partial load to store
 * forwarding cases (a store only has part of a load's data) that requires
 * the load to wait until the store writes back. In the former case it
 * holds onto the instruction until the dependence unit looks at it, and
 * in the latter it stalls the LSQ until the store writes back. At that
 * point the load is replayed.
 */
template <class Impl>
class LSQUnit {
  protected:
    typedef TheISA::IntReg IntReg;
  public:
    typedef typename Impl::Params Params;
    typedef typename Impl::FullCPU FullCPU;
    typedef typename Impl::DynInstPtr DynInstPtr;
    typedef typename Impl::CPUPol::IEW IEW;
    typedef typename Impl::CPUPol::IssueStruct IssueStruct;

  private:
    class StoreCompletionEvent : public Event {
      public:
        /** Constructs a store completion event. */
        StoreCompletionEvent(int store_idx, Event *wb_event, LSQUnit *lsq_ptr);

        /** Processes the store completion event. */
        void process();

        /** Returns the description of this event. */
        const char *description();

      private:
        /** The store index of the store being written back. */
        int storeIdx;
        /** The writeback event for the store.  Needed for store
         * conditionals.
         */
        Event *wbEvent;
        /** The pointer to the LSQ unit that issued the store. */
        LSQUnit<Impl> *lsqPtr;
    };

    friend class StoreCompletionEvent;

  public:
    /** Constructs an LSQ unit. init() must be called prior to use. */
    LSQUnit();

    /** Initializes the LSQ unit with the specified number of entries. */
    void init(Params *params, unsigned maxLQEntries,
              unsigned maxSQEntries, unsigned id);

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

    /** Sets the CPU pointer. */
    void setCPU(FullCPU *cpu_ptr)
    { cpu = cpu_ptr; }

    /** Sets the IEW stage pointer. */
    void setIEW(IEW *iew_ptr)
    { iewStage = iew_ptr; }

    /** Sets the page table pointer. */
//    void setPageTable(PageTable *pt_ptr);

    /** Ticks the LSQ unit, which in this case only resets the number of
     * used cache ports.
     * @todo: Move the number of used ports up to the LSQ level so it can
     * be shared by all LSQ units.
     */
    void tick() { usedPorts = 0; }

    /** Inserts an instruction. */
    void insert(DynInstPtr &inst);
    /** Inserts a load instruction. */
    void insertLoad(DynInstPtr &load_inst);
    /** Inserts a store instruction. */
    void insertStore(DynInstPtr &store_inst);

    /** Executes a load instruction. */
    Fault executeLoad(DynInstPtr &inst);

    Fault executeLoad(int lq_idx);
    /** Executes a store instruction. */
    Fault executeStore(DynInstPtr &inst);

    /** Commits the head load. */
    void commitLoad();
    /** Commits a specific load, given by the sequence number. */
    void commitLoad(InstSeqNum &inst);
    /** Commits loads older than a specific sequence number. */
    void commitLoads(InstSeqNum &youngest_inst);

    /** Commits stores older than a specific sequence number. */
    void commitStores(InstSeqNum &youngest_inst);

    /** Writes back stores. */
    void writebackStores();

    // @todo: Include stats in the LSQ unit.
    //void regStats();

    /** Clears all the entries in the LQ. */
    void clearLQ();

    /** Clears all the entries in the SQ. */
    void clearSQ();

    /** Resizes the LQ to a given size. */
    void resizeLQ(unsigned size);

    /** Resizes the SQ to a given size. */
    void resizeSQ(unsigned size);

    /** Squashes all instructions younger than a specific sequence number. */
    void squash(const InstSeqNum &squashed_num);

    /** Returns if there is a memory ordering violation. Value is reset upon
     * call to getMemDepViolator().
     */
    bool violation() { return memDepViolator; }

    /** Returns the memory ordering violator. */
    DynInstPtr getMemDepViolator();

    /** Returns if a load became blocked due to the memory system.  It clears
     *  the bool's value upon this being called.
     */
    bool loadBlocked()
    { return isLoadBlocked; }

    void clearLoadBlocked()
    { isLoadBlocked = false; }

    bool isLoadBlockedHandled()
    { return loadBlockedHandled; }

    void setLoadBlockedHandled()
    { loadBlockedHandled = true; }

    /** Returns the number of free entries (min of free LQ and SQ entries). */
    unsigned numFreeEntries();

    /** Returns the number of loads ready to execute. */
    int numLoadsReady();

    /** Returns the number of loads in the LQ. */
    int numLoads() { return loads; }

    /** Returns the number of stores in the SQ. */
    int numStores() { return stores; }

    /** Returns if either the LQ or SQ is full. */
    bool isFull() { return lqFull() || sqFull(); }

    /** Returns if the LQ is full. */
    bool lqFull() { return loads >= (LQEntries - 1); }

    /** Returns if the SQ is full. */
    bool sqFull() { return stores >= (SQEntries - 1); }

    /** Debugging function to dump instructions in the LSQ. */
    void dumpInsts();

    /** Returns the number of instructions in the LSQ. */
    unsigned getCount() { return loads + stores; }

    /** Returns if there are any stores to writeback. */
    bool hasStoresToWB() { return storesToWB; }

    /** Returns the number of stores to writeback. */
    int numStoresToWB() { return storesToWB; }

    /** Returns if the LSQ unit will writeback on this cycle. */
    bool willWB() { return storeQueue[storeWBIdx].canWB &&
                        !storeQueue[storeWBIdx].completed &&
                        !dcacheInterface->isBlocked(); }

  private:
    /** Completes the store at the specified index. */
    void completeStore(int store_idx);

    /** Increments the given store index (circular queue). */
    inline void incrStIdx(int &store_idx);
    /** Decrements the given store index (circular queue). */
    inline void decrStIdx(int &store_idx);
    /** Increments the given load index (circular queue). */
    inline void incrLdIdx(int &load_idx);
    /** Decrements the given load index (circular queue). */
    inline void decrLdIdx(int &load_idx);

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

    /** Pointer to the IEW stage. */
    IEW *iewStage;

    /** Pointer to the D-cache. */
    MemInterface *dcacheInterface;

    /** Pointer to the page table. */
//    PageTable *pTable;

  public:
    struct SQEntry {
        /** Constructs an empty store queue entry. */
        SQEntry()
            : inst(NULL), req(NULL), size(0), data(0),
              canWB(0), committed(0), completed(0)
        { }

        /** Constructs a store queue entry for a given instruction. */
        SQEntry(DynInstPtr &_inst)
            : inst(_inst), req(NULL), size(0), data(0),
              canWB(0), committed(0), completed(0)
        { }

        /** The store instruction. */
        DynInstPtr inst;
        /** The memory request for the store. */
        MemReqPtr req;
        /** The size of the store. */
        int size;
        /** The store data. */
        IntReg data;
        /** Whether or not the store can writeback. */
        bool canWB;
        /** Whether or not the store is committed. */
        bool committed;
        /** Whether or not the store is completed. */
        bool completed;
    };

    enum Status {
        Running,
        Idle,
        DcacheMissStall,
        DcacheMissSwitch
    };

  private:
    /** The LSQUnit thread id. */
    unsigned lsqID;

    /** The status of the LSQ unit. */
    Status _status;

    /** The store queue. */
    std::vector<SQEntry> storeQueue;

    /** The load queue. */
    std::vector<DynInstPtr> loadQueue;

    // Consider making these 16 bits
    /** The number of LQ entries. */
    unsigned LQEntries;
    /** The number of SQ entries. */
    unsigned SQEntries;

    /** The number of load instructions in the LQ. */
    int loads;
    /** The number of store instructions in the SQ (excludes those waiting to
     * writeback).
     */
    int stores;
    /** The number of store instructions in the SQ waiting to writeback. */
    int storesToWB;

    /** The index of the head instruction in the LQ. */
    int loadHead;
    /** The index of the tail instruction in the LQ. */
    int loadTail;

    /** The index of the head instruction in the SQ. */
    int storeHead;
    /** The index of the first instruction that is ready to be written back,
     * and has not yet been written back.
     */
    int storeWBIdx;
    /** The index of the tail instruction in the SQ. */
    int storeTail;

    /// @todo Consider moving to a more advanced model with write vs read ports
    /** The number of cache ports available each cycle. */
    int cachePorts;

    /** The number of used cache ports in this cycle. */
    int usedPorts;

    //list<InstSeqNum> mshrSeqNums;

     //Stats::Scalar<> dcacheStallCycles;
    Counter lastDcacheStall;

    /** Wire to read information from the issue stage time queue. */
    typename TimeBuffer<IssueStruct>::wire fromIssue;

    // Make these per thread?
    /** Whether or not the LSQ is stalled. */
    bool stalled;
    /** The store that causes the stall due to partial store to load
     * forwarding.
     */
    InstSeqNum stallingStoreIsn;
    /** The index of the above store. */
    int stallingLoadIdx;

    /** Whether or not a load is blocked due to the memory system.  It is
     *  cleared when this value is checked via loadBlocked().
     */
    bool isLoadBlocked;

    bool loadBlockedHandled;

    InstSeqNum blockedLoadSeqNum;

    /** The oldest faulting load instruction. */
    DynInstPtr loadFaultInst;
    /** The oldest faulting store instruction. */
    DynInstPtr storeFaultInst;

    /** The oldest load that caused a memory ordering violation. */
    DynInstPtr memDepViolator;

    // Will also need how many read/write ports the Dcache has.  Or keep track
    // of that in stage that is one level up, and only call executeLoad/Store
    // the appropriate number of times.

  public:
    /** Executes the load at the given index. */
    template <class T>
    Fault read(MemReqPtr &req, T &data, int load_idx);

    /** Executes the store at the given index. */
    template <class T>
    Fault write(MemReqPtr &req, T &data, int store_idx);

    /** Returns the index of the head load instruction. */
    int getLoadHead() { return loadHead; }
    /** Returns the sequence number of the head load instruction. */
    InstSeqNum getLoadHeadSeqNum()
    {
        if (loadQueue[loadHead]) {
            return loadQueue[loadHead]->seqNum;
        } else {
            return 0;
        }

    }

    /** Returns the index of the head store instruction. */
    int getStoreHead() { return storeHead; }
    /** Returns the sequence number of the head store instruction. */
    InstSeqNum getStoreHeadSeqNum()
    {
        if (storeQueue[storeHead].inst) {
            return storeQueue[storeHead].inst->seqNum;
        } else {
            return 0;
        }

    }

    /** Returns whether or not the LSQ unit is stalled. */
    bool isStalled()  { return stalled; }
};

template <class Impl>
template <class T>
Fault
LSQUnit<Impl>::read(MemReqPtr &req, T &data, int load_idx)
{
    //Depending on issue2execute delay a squashed load could
    //execute if it is found to be squashed in the same
    //cycle it is scheduled to execute
    assert(loadQueue[load_idx]);

    if (loadQueue[load_idx]->isExecuted()) {
        panic("Should not reach this point with split ops!");
        memcpy(&data,req->data,req->size);

        return NoFault;
    }

    // Make sure this isn't an uncacheable access
    // A bit of a hackish way to get uncached accesses to work only if they're
    // at the head of the LSQ and are ready to commit (at the head of the ROB
    // too).
    // @todo: Fix uncached accesses.
    if (req->flags & UNCACHEABLE &&
        (load_idx != loadHead || !loadQueue[load_idx]->reachedCommit)) {
        iewStage->rescheduleMemInst(loadQueue[load_idx]);
        return TheISA::genMachineCheckFault();
    }

    // Check the SQ for any previous stores that might lead to forwarding
    int store_idx = loadQueue[load_idx]->sqIdx;

    int store_size = 0;

    DPRINTF(LSQUnit, "Read called, load idx: %i, store idx: %i, "
            "storeHead: %i addr: %#x\n",
            load_idx, store_idx, storeHead, req->paddr);

#ifdef FULL_SYSTEM
    if (req->flags & LOCKED) {
        cpu->lockAddr = req->paddr;
        cpu->lockFlag = true;
    }
#endif

    while (store_idx != -1) {
        // End once we've reached the top of the LSQ
        if (store_idx == storeWBIdx) {
            break;
        }

        // Move the index to one younger
        if (--store_idx < 0)
            store_idx += SQEntries;

        assert(storeQueue[store_idx].inst);

        store_size = storeQueue[store_idx].size;

        if (store_size == 0)
            continue;

        // Check if the store data is within the lower and upper bounds of
        // addresses that the request needs.
        bool store_has_lower_limit =
            req->vaddr >= storeQueue[store_idx].inst->effAddr;
        bool store_has_upper_limit =
            (req->vaddr + req->size) <= (storeQueue[store_idx].inst->effAddr +
                                         store_size);
        bool lower_load_has_store_part =
            req->vaddr < (storeQueue[store_idx].inst->effAddr +
                           store_size);
        bool upper_load_has_store_part =
            (req->vaddr + req->size) > storeQueue[store_idx].inst->effAddr;

        // If the store's data has all of the data needed, we can forward.
        if (store_has_lower_limit && store_has_upper_limit) {

            int shift_amt = req->vaddr & (store_size - 1);
            // Assumes byte addressing
            shift_amt = shift_amt << 3;

            // Cast this to type T?
            data = storeQueue[store_idx].data >> shift_amt;

            req->cmd = Read;
            assert(!req->completionEvent);
            req->completionEvent = NULL;
            req->time = curTick;
            assert(!req->data);
            req->data = new uint8_t[64];

            memcpy(req->data, &data, req->size);

            DPRINTF(LSQUnit, "Forwarding from store idx %i to load to "
                    "addr %#x, data %#x\n",
                    store_idx, req->vaddr, *(req->data));

            typename IEW::LdWritebackEvent *wb =
                new typename IEW::LdWritebackEvent(loadQueue[load_idx],
                                                   iewStage);

            // We'll say this has a 1 cycle load-store forwarding latency
            // for now.
            // @todo: Need to make this a parameter.
            wb->schedule(curTick);

            // Should keep track of stat for forwarded data
            return NoFault;
        } else if ((store_has_lower_limit && lower_load_has_store_part) ||
                   (store_has_upper_limit && upper_load_has_store_part) ||
                   (lower_load_has_store_part && upper_load_has_store_part)) {
            // This is the partial store-load forwarding case where a store
            // has only part of the load's data.

            // If it's already been written back, then don't worry about
            // stalling on it.
            if (storeQueue[store_idx].completed) {
                continue;
            }

            // Must stall load and force it to retry, so long as it's the oldest
            // load that needs to do so.
            if (!stalled ||
                (stalled &&
                 loadQueue[load_idx]->seqNum <
                 loadQueue[stallingLoadIdx]->seqNum)) {
                stalled = true;
                stallingStoreIsn = storeQueue[store_idx].inst->seqNum;
                stallingLoadIdx = load_idx;
            }

            // Tell IQ/mem dep unit that this instruction will need to be
            // rescheduled eventually
            iewStage->rescheduleMemInst(loadQueue[load_idx]);

            // Do not generate a writeback event as this instruction is not
            // complete.

            DPRINTF(LSQUnit, "Load-store forwarding mis-match. "
                    "Store idx %i to load addr %#x\n",
                    store_idx, req->vaddr);

            return NoFault;
        }
    }


    // If there's no forwarding case, then go access memory
    DynInstPtr inst = loadQueue[load_idx];

    DPRINTF(LSQUnit, "Doing functional access for inst PC %#x\n",
            loadQueue[load_idx]->readPC());
    assert(!req->data);
    req->data = new uint8_t[64];
    Fault fault = cpu->read(req, data);
    memcpy(req->data, &data, sizeof(T));

    ++usedPorts;

    // if we have a cache, do cache access too
    if (fault == NoFault && dcacheInterface) {
        if (dcacheInterface->isBlocked()) {
            // There's an older load that's already going to squash.
            if (isLoadBlocked && blockedLoadSeqNum < inst->seqNum)
                return NoFault;

            isLoadBlocked = true;
            loadBlockedHandled = false;
            blockedLoadSeqNum = inst->seqNum;
            // No fault occurred, even though the interface is blocked.
            return NoFault;
        }
        DPRINTF(LSQUnit, "Doing timing access for inst PC %#x\n",
                loadQueue[load_idx]->readPC());
        req->cmd = Read;
        req->completionEvent = NULL;
        req->time = curTick;

        assert(!req->completionEvent);
        req->completionEvent =
            new typename IEW::LdWritebackEvent(loadQueue[load_idx], iewStage);
        MemAccessResult result = dcacheInterface->access(req);

        assert(dcacheInterface->doEvents());

        // Ugly hack to get an event scheduled *only* if the access is
        // a miss.  We really should add first-class support for this
        // at some point.
        if (result != MA_HIT) {
            DPRINTF(LSQUnit, "LSQUnit: D-cache miss!\n");
            DPRINTF(Activity, "Activity: ld accessing mem miss [sn:%lli]\n",
                    inst->seqNum);

            lastDcacheStall = curTick;

            _status = DcacheMissStall;

        } else {
            DPRINTF(Activity, "Activity: ld accessing mem hit [sn:%lli]\n",
                    inst->seqNum);

            DPRINTF(LSQUnit, "LSQUnit: D-cache hit!\n");
        }
    }
#if 0
    // if we have a cache, do cache access too
    if (dcacheInterface) {
        if (dcacheInterface->isBlocked()) {
            isLoadBlocked = true;
            // No fault occurred, even though the interface is blocked.
            return NoFault;
        }

        DPRINTF(LSQUnit, "LSQUnit: D-cache: PC:%#x reading from paddr:%#x "
                "vaddr:%#x flags:%i\n",
                inst->readPC(), req->paddr, req->vaddr, req->flags);

        // Setup MemReq pointer
        req->cmd = Read;
        req->completionEvent = NULL;
        req->time = curTick;
        assert(!req->data);
        req->data = new uint8_t[64];

        assert(!req->completionEvent);
        req->completionEvent =
            new typename IEW::LdWritebackEvent(loadQueue[load_idx], iewStage);

        // Do Cache Access
        MemAccessResult result = dcacheInterface->access(req);

        // Ugly hack to get an event scheduled *only* if the access is
        // a miss.  We really should add first-class support for this
        // at some point.
        // @todo: Probably should support having no events
        if (result != MA_HIT) {
            DPRINTF(LSQUnit, "LSQUnit: D-cache miss!\n");
            DPRINTF(Activity, "Activity: ld accessing mem miss [sn:%lli]\n",
                    inst->seqNum);

            lastDcacheStall = curTick;

            _status = DcacheMissStall;

        } else {
            DPRINTF(Activity, "Activity: ld accessing mem hit [sn:%lli]\n",
                    inst->seqNum);

            DPRINTF(LSQUnit, "LSQUnit: D-cache hit!\n");
        }
    } else {
        fatal("Must use D-cache with new memory system");
    }
#endif

    return fault;
}

template <class Impl>
template <class T>
Fault
LSQUnit<Impl>::write(MemReqPtr &req, T &data, int store_idx)
{
    assert(storeQueue[store_idx].inst);

    DPRINTF(LSQUnit, "Doing write to store idx %i, addr %#x data %#x"
            " | storeHead:%i [sn:%i]\n",
            store_idx, req->paddr, data, storeHead,
            storeQueue[store_idx].inst->seqNum);
/*
    if (req->flags & LOCKED) {
        if (req->flags & UNCACHEABLE) {
            req->result = 2;
        } else {
            req->result = 1;
        }
    }
*/
    storeQueue[store_idx].req = req;
    storeQueue[store_idx].size = sizeof(T);
    storeQueue[store_idx].data = data;

    // This function only writes the data to the store queue, so no fault
    // can happen here.
    return NoFault;
}

#endif // __CPU_O3_LSQ_UNIT_HH__