rob.cc

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#include "cpu/o3/rob.hh"
 
#include <list>
 
#include "base/logging.hh"
#include "cpu/o3/dyn_inst.hh"
#include "cpu/o3/limits.hh"
#include "debug/Fetch.hh"
#include "debug/ROB.hh"
#include "params/BaseO3CPU.hh"
 
namespace gem5
{
 
namespace o3
{
 
ROB::ROB(CPU *_cpu, const BaseO3CPUParams &params)
    : robPolicy(params.smtROBPolicy),
      cpu(_cpu),
      numEntries(params.numROBEntries),
      squashWidth(params.squashWidth),
      numInstsInROB(0),
      numThreads(params.numThreads),
      stats(_cpu)
{
    //Figure out rob policy
    if (robPolicy == SMTQueuePolicy::Dynamic) {
        //Set Max Entries to Total ROB Capacity
        for (ThreadID tid = 0; tid < numThreads; tid++) {
            maxEntries[tid] = numEntries;
        }
 
    } else if (robPolicy == SMTQueuePolicy::Partitioned) {
        DPRINTF(Fetch, "ROB sharing policy set to Partitioned\n");
 
        //@todo:make work if part_amt doesnt divide evenly.
        int part_amt = numEntries / numThreads;
 
        //Divide ROB up evenly
        for (ThreadID tid = 0; tid < numThreads; tid++) {
            maxEntries[tid] = part_amt;
        }
 
    } else if (robPolicy == SMTQueuePolicy::Threshold) {
        DPRINTF(Fetch, "ROB sharing policy set to Threshold\n");
 
        int threshold =  params.smtROBThreshold;;
 
        //Divide up by threshold amount
        for (ThreadID tid = 0; tid < numThreads; tid++) {
            maxEntries[tid] = threshold;
        }
    }
 
    for (ThreadID tid = numThreads; tid < MaxThreads; tid++) {
        maxEntries[tid] = 0;
    }
 
    resetState();
}
 
void
ROB::resetState()
{
    for (ThreadID tid = 0; tid  < MaxThreads; tid++) {
        threadEntries[tid] = 0;
        squashIt[tid] = instList[tid].end();
        squashedSeqNum[tid] = 0;
        doneSquashing[tid] = true;
    }
    numInstsInROB = 0;
 
    // Initialize the "universal" ROB head & tail point to invalid
    // pointers
    head = instList[0].end();
    tail = instList[0].end();
}
 
std::string
ROB::name() const
{
    return cpu->name() + ".rob";
}
 
void
ROB::setActiveThreads(std::list<ThreadID> *at_ptr)
{
    DPRINTF(ROB, "Setting active threads list pointer.\n");
    activeThreads = at_ptr;
}
 
void
ROB::drainSanityCheck() const
{
    for (ThreadID tid = 0; tid  < numThreads; tid++)
        assert(instList[tid].empty());
    assert(isEmpty());
}
 
void
ROB::takeOverFrom()
{
    resetState();
}
 
void
ROB::resetEntries()
{
    if (robPolicy != SMTQueuePolicy::Dynamic || numThreads > 1) {
        auto active_threads = activeThreads->size();
 
        for (ThreadID tid : *activeThreads) {
            if (robPolicy == SMTQueuePolicy::Partitioned) {
                maxEntries[tid] = numEntries / active_threads;
            } else if (robPolicy == SMTQueuePolicy::Threshold &&
                       active_threads == 1) {
                maxEntries[tid] = numEntries;
            }
        }
    }
}
 
int
ROB::entryAmount(ThreadID num_threads)
{
    if (robPolicy == SMTQueuePolicy::Partitioned) {
        return numEntries / num_threads;
    } else {
        return 0;
    }
}
 
int
ROB::countInsts()
{
    int total = 0;
 
    for (ThreadID tid = 0; tid < numThreads; tid++)
        total += countInsts(tid);
 
    return total;
}
 
size_t
ROB::countInsts(ThreadID tid)
{
    return instList[tid].size();
}
 
void
ROB::insertInst(const DynInstPtr &inst)
{
    assert(inst);
 
    stats.writes++;
 
    DPRINTF(ROB, "Adding inst PC %s to the ROB.\n", inst->pcState());
 
    assert(numInstsInROB != numEntries);
 
    ThreadID tid = inst->threadNumber;
 
    instList[tid].push_back(inst);
 
    //Set Up head iterator if this is the 1st instruction in the ROB
    if (numInstsInROB == 0) {
        head = instList[tid].begin();
        assert((*head) == inst);
    }
 
    //Must Decrement for iterator to actually be valid  since __.end()
    //actually points to 1 after the last inst
    tail = instList[tid].end();
    tail--;
 
    inst->setInROB();
 
    ++numInstsInROB;
    ++threadEntries[tid];
 
    assert((*tail) == inst);
 
    DPRINTF(ROB, "[tid:%i] Now has %d instructions.\n", tid,
            threadEntries[tid]);
}
 
void
ROB::retireHead(ThreadID tid)
{
    stats.writes++;
 
    assert(numInstsInROB > 0);
 
    // Get the head ROB instruction by copying it and remove it from the list
    InstIt head_it = instList[tid].begin();
 
    DynInstPtr head_inst = std::move(*head_it);
    instList[tid].erase(head_it);
 
    assert(head_inst->readyToCommit());
 
    DPRINTF(ROB, "[tid:%i] Retiring head instruction, "
            "instruction PC %s, [sn:%llu]\n", tid, head_inst->pcState(),
            head_inst->seqNum);
 
    --numInstsInROB;
    --threadEntries[tid];
 
    head_inst->clearInROB();
    head_inst->setCommitted();
 
    //Update "Global" Head of ROB
    updateHead();
 
    // @todo: A special case is needed if the instruction being
    // retired is the only instruction in the ROB; otherwise the tail
    // iterator will become invalidated.
    cpu->removeFrontInst(head_inst);
}
 
bool
ROB::isHeadReady(ThreadID tid)
{
    stats.reads++;
    if (threadEntries[tid] != 0) {
        return instList[tid].front()->readyToCommit();
    }
 
    return false;
}
 
bool
ROB::canCommit()
{
    //@todo: set ActiveThreads through ROB or CPU
    for (ThreadID tid : *activeThreads) {
        if (isHeadReady(tid)) {
            return true;
        }
    }
 
    return false;
}
 
unsigned
ROB::numFreeEntries()
{
    return numEntries - numInstsInROB;
}
 
unsigned
ROB::numFreeEntries(ThreadID tid)
{
    return maxEntries[tid] - threadEntries[tid];
}
 
void
ROB::doSquash(ThreadID tid)
{
    stats.writes++;
    DPRINTF(ROB, "[tid:%i] Squashing instructions until [sn:%llu].\n",
            tid, squashedSeqNum[tid]);
 
    assert(squashIt[tid] != instList[tid].end());
 
    if ((*squashIt[tid])->seqNum < squashedSeqNum[tid]) {
        DPRINTF(ROB, "[tid:%i] Done squashing instructions.\n",
                tid);
 
        squashIt[tid] = instList[tid].end();
 
        doneSquashing[tid] = true;
        return;
    }
 
    bool robTailUpdate = false;
 
    unsigned int numInstsToSquash = squashWidth;
 
    // If the CPU is exiting, squash all of the instructions
    // it is told to, even if that exceeds the squashWidth.
    // Set the number to the number of entries (the max).
    if (cpu->isThreadExiting(tid))
    {
        numInstsToSquash = numEntries;
    }
 
    for (int numSquashed = 0;
         numSquashed < numInstsToSquash &&
         squashIt[tid] != instList[tid].end() &&
         (*squashIt[tid])->seqNum > squashedSeqNum[tid];
         ++numSquashed)
    {
        DPRINTF(ROB, "[tid:%i] Squashing instruction PC %s, seq num %i.\n",
                (*squashIt[tid])->threadNumber,
                (*squashIt[tid])->pcState(),
                (*squashIt[tid])->seqNum);
 
        // Mark the instruction as squashed, and ready to commit so that
        // it can drain out of the pipeline.
        (*squashIt[tid])->setSquashed();
 
        (*squashIt[tid])->setCanCommit();
 
 
        if (squashIt[tid] == instList[tid].begin()) {
            DPRINTF(ROB, "Reached head of instruction list while "
                    "squashing.\n");
 
            squashIt[tid] = instList[tid].end();
 
            doneSquashing[tid] = true;
 
            return;
        }
 
        InstIt tail_thread = instList[tid].end();
        tail_thread--;
 
        if ((*squashIt[tid]) == (*tail_thread))
            robTailUpdate = true;
 
        squashIt[tid]--;
    }
 
 
    // Check if ROB is done squashing.
    if ((*squashIt[tid])->seqNum <= squashedSeqNum[tid]) {
        DPRINTF(ROB, "[tid:%i] Done squashing instructions.\n",
                tid);
 
        squashIt[tid] = instList[tid].end();
 
        doneSquashing[tid] = true;
    }
 
    if (robTailUpdate) {
        updateTail();
    }
}
 
 
void
ROB::updateHead()
{
    InstSeqNum lowest_num = 0;
    bool first_valid = true;
 
    // @todo: set ActiveThreads through ROB or CPU
    for (ThreadID tid : *activeThreads) {
        if (instList[tid].empty())
            continue;
 
        if (first_valid) {
            head = instList[tid].begin();
            lowest_num = (*head)->seqNum;
            first_valid = false;
            continue;
        }
 
        InstIt head_thread = instList[tid].begin();
 
        DynInstPtr head_inst = (*head_thread);
 
        assert(head_inst != 0);
 
        if (head_inst->seqNum < lowest_num) {
            head = head_thread;
            lowest_num = head_inst->seqNum;
        }
    }
 
    if (first_valid) {
        head = instList[0].end();
    }
 
}
 
void
ROB::updateTail()
{
    tail = instList[0].end();
    bool first_valid = true;
 
    for (ThreadID tid : *activeThreads) {
        if (instList[tid].empty()) {
            continue;
        }
 
        // If this is the first valid then assign w/out
        // comparison
        if (first_valid) {
            tail = instList[tid].end();
            tail--;
            first_valid = false;
            continue;
        }
 
        // Assign new tail if this thread's tail is younger
        // than our current "tail high"
        InstIt tail_thread = instList[tid].end();
        tail_thread--;
 
        if ((*tail_thread)->seqNum > (*tail)->seqNum) {
            tail = tail_thread;
        }
    }
}
 
 
void
ROB::squash(InstSeqNum squash_num, ThreadID tid)
{
    if (isEmpty(tid)) {
        DPRINTF(ROB, "Does not need to squash due to being empty "
                "[sn:%llu]\n",
                squash_num);
 
        return;
    }
 
    DPRINTF(ROB, "Starting to squash within the ROB.\n");
 
    robStatus[tid] = ROBSquashing;
 
    doneSquashing[tid] = false;
 
    squashedSeqNum[tid] = squash_num;
 
    if (!instList[tid].empty()) {
        InstIt tail_thread = instList[tid].end();
        tail_thread--;
 
        squashIt[tid] = tail_thread;
 
        doSquash(tid);
    }
}
 
const DynInstPtr&
ROB::readHeadInst(ThreadID tid)
{
    if (threadEntries[tid] != 0) {
        InstIt head_thread = instList[tid].begin();
 
        assert((*head_thread)->isInROB());
 
        return *head_thread;
    } else {
        return dummyInst;
    }
}
 
DynInstPtr
ROB::readTailInst(ThreadID tid)
{
    InstIt tail_thread = instList[tid].end();
    tail_thread--;
 
    return *tail_thread;
}
 
ROB::ROBStats::ROBStats(statistics::Group *parent)
  : statistics::Group(parent, "rob"),
    ADD_STAT(reads, statistics::units::Count::get(),
        "The number of ROB reads"),
    ADD_STAT(writes, statistics::units::Count::get(),
        "The number of ROB writes")
{
}
 
DynInstPtr
ROB::findInst(ThreadID tid, InstSeqNum squash_inst)
{
    for (InstIt it = instList[tid].begin(); it != instList[tid].end(); it++) {
        if ((*it)->seqNum == squash_inst) {
            return *it;
        }
    }
    return NULL;
}
 
} // namespace o3
} // namespace gem5