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Diffstat (limited to 'cpu/beta_cpu/fetch_impl.hh')
| -rw-r--r-- | cpu/beta_cpu/fetch_impl.hh | 599 |
1 files changed, 599 insertions, 0 deletions
diff --git a/cpu/beta_cpu/fetch_impl.hh b/cpu/beta_cpu/fetch_impl.hh new file mode 100644 index 000000000..90caf9ffe --- /dev/null +++ b/cpu/beta_cpu/fetch_impl.hh @@ -0,0 +1,599 @@ +// Remove this later; used only for debugging. +#define OPCODE(X) (X >> 26) & 0x3f + + +#include "arch/alpha/byte_swap.hh" +#include "cpu/exetrace.hh" +#include "mem/base_mem.hh" +#include "mem/mem_interface.hh" +#include "mem/mem_req.hh" +#include "cpu/beta_cpu/fetch.hh" + +#include "sim/universe.hh" + +template<class Impl> +SimpleFetch<Impl>::CacheCompletionEvent +::CacheCompletionEvent(SimpleFetch *_fetch) + : Event(&mainEventQueue), + fetch(_fetch) +{ +} + +template<class Impl> +void +SimpleFetch<Impl>::CacheCompletionEvent::process() +{ + fetch->processCacheCompletion(); +} + +template<class Impl> +const char * +SimpleFetch<Impl>::CacheCompletionEvent::description() +{ + return "SimpleFetch cache completion event"; +} + +template<class Impl> +SimpleFetch<Impl>::SimpleFetch(Params ¶ms) + : //cacheCompletionEvent(this), + icacheInterface(params.icacheInterface), + branchPred(params), + decodeToFetchDelay(params.decodeToFetchDelay), + renameToFetchDelay(params.renameToFetchDelay), + iewToFetchDelay(params.iewToFetchDelay), + commitToFetchDelay(params.commitToFetchDelay), + fetchWidth(params.fetchWidth) +{ + // Set status to idle. + _status = Idle; + + // Create a new memory request. + memReq = new MemReq(); + // Not sure of this parameter. I think it should be based on the + // thread number. +#ifndef FULL_SYSTEM + memReq->asid = params.asid; +#else + memReq->asid = 0; +#endif // FULL_SYSTEM + memReq->data = new uint8_t[64]; + + // Size of cache block. + cacheBlkSize = icacheInterface ? icacheInterface->getBlockSize() : 64; + + // Create mask to get rid of offset bits. + cacheBlkMask = (cacheBlkSize - 1); + + // Get the size of an instruction. + instSize = sizeof(MachInst); + + // Create space to store a cache line. + cacheData = new uint8_t[cacheBlkSize]; +} + +template <class Impl> +void +SimpleFetch<Impl>::regStats() +{ + icacheStallCycles + .name(name() + ".icacheStallCycles") + .desc("Number of cycles fetch is stalled on an Icache miss") + .prereq(icacheStallCycles); + + fetchedInsts + .name(name() + ".fetchedInsts") + .desc("Number of instructions fetch has processed") + .prereq(fetchedInsts); + predictedBranches + .name(name() + ".predictedBranches") + .desc("Number of branches that fetch has predicted taken") + .prereq(predictedBranches); + fetchCycles + .name(name() + ".fetchCycles") + .desc("Number of cycles fetch has run and was not squashing or" + " blocked") + .prereq(fetchCycles); + fetchSquashCycles + .name(name() + ".fetchSquashCycles") + .desc("Number of cycles fetch has spent squashing") + .prereq(fetchSquashCycles); + fetchBlockedCycles + .name(name() + ".fetchBlockedCycles") + .desc("Number of cycles fetch has spent blocked") + .prereq(fetchBlockedCycles); + fetchedCacheLines + .name(name() + ".fetchedCacheLines") + .desc("Number of cache lines fetched") + .prereq(fetchedCacheLines); + + fetch_nisn_dist + .init(/* base value */ 0, + /* last value */ fetchWidth, + /* bucket size */ 1) + .name(name() + ".FETCH:rate_dist") + .desc("Number of instructions fetched each cycle (Total)") + .flags(Stats::pdf) + ; + + branchPred.regStats(); +} + +template<class Impl> +void +SimpleFetch<Impl>::setCPU(FullCPU *cpu_ptr) +{ + DPRINTF(Fetch, "Fetch: Setting the CPU pointer.\n"); + cpu = cpu_ptr; + // This line will be removed eventually. + memReq->xc = cpu->xcBase(); +} + +template<class Impl> +void +SimpleFetch<Impl>::setTimeBuffer(TimeBuffer<TimeStruct> *time_buffer) +{ + DPRINTF(Fetch, "Fetch: Setting the time buffer pointer.\n"); + timeBuffer = time_buffer; + + // Create wires to get information from proper places in time buffer. + fromDecode = timeBuffer->getWire(-decodeToFetchDelay); + fromRename = timeBuffer->getWire(-renameToFetchDelay); + fromIEW = timeBuffer->getWire(-iewToFetchDelay); + fromCommit = timeBuffer->getWire(-commitToFetchDelay); +} + +template<class Impl> +void +SimpleFetch<Impl>::setFetchQueue(TimeBuffer<FetchStruct> *fq_ptr) +{ + DPRINTF(Fetch, "Fetch: Setting the fetch queue pointer.\n"); + fetchQueue = fq_ptr; + + // Create wire to write information to proper place in fetch queue. + toDecode = fetchQueue->getWire(0); +} + +template<class Impl> +void +SimpleFetch<Impl>::processCacheCompletion() +{ + DPRINTF(Fetch, "Fetch: Waking up from cache miss.\n"); + + // Only change the status if it's still waiting on the icache access + // to return. + // Can keep track of how many cache accesses go unused due to + // misspeculation here. + // How to handle an outstanding miss which gets cancelled due to squash, + // then a new icache miss gets scheduled? + if (_status == IcacheMissStall) + _status = IcacheMissComplete; +} + +#if 0 +template <class Impl> +inline void +SimpleFetch<Impl>::recordGlobalHist(DynInstPtr &inst) +{ + inst->setGlobalHist(branchPred.BPReadGlobalHist()); +} +#endif + +template <class Impl> +bool +SimpleFetch<Impl>::lookupAndUpdateNextPC(DynInstPtr &inst, Addr &next_PC) +{ + // Do branch prediction check here. + // A bit of a misnomer...next_PC is actually the current PC until + // this function updates it. + bool predict_taken; + + if (!inst->isControl()) { + next_PC = next_PC + instSize; + inst->setPredTarg(next_PC); + return false; + } + + predict_taken = branchPred.predict(inst, next_PC); + + if (predict_taken) { + ++predictedBranches; + } + + return predict_taken; +} + +template <class Impl> +Fault +SimpleFetch<Impl>::fetchCacheLine(Addr fetch_PC) +{ + // Check if the instruction exists within the cache. + // If it does, then proceed on to read the instruction and the rest + // of the instructions in the cache line until either the end of the + // cache line or a predicted taken branch is encountered. + +#ifdef FULL_SYSTEM + // Flag to say whether or not address is physical addr. + unsigned flags = cpu->inPalMode() ? PHYSICAL : 0; +#else + unsigned flags = 0; +#endif // FULL_SYSTEM + + Fault fault = No_Fault; + + // Align the fetch PC so it's at the start of a cache block. + fetch_PC = icacheBlockAlignPC(fetch_PC); + + // Setup the memReq to do a read of the first isntruction's address. + // Set the appropriate read size and flags as well. + memReq->cmd = Read; + memReq->reset(fetch_PC, cacheBlkSize, flags); + + // Translate the instruction request. + // Should this function be + // in the CPU class ? Probably...ITB/DTB should exist within the + // CPU. + + fault = cpu->translateInstReq(memReq); + + // In the case of faults, the fetch stage may need to stall and wait + // on what caused the fetch (ITB or Icache miss). + + // If translation was successful, attempt to read the first + // instruction. + if (fault == No_Fault) { + DPRINTF(Fetch, "Fetch: Doing instruction read.\n"); + fault = cpu->mem->read(memReq, cacheData); + // This read may change when the mem interface changes. + + fetchedCacheLines++; + } + + // Now do the timing access to see whether or not the instruction + // exists within the cache. + if (icacheInterface && fault == No_Fault) { + DPRINTF(Fetch, "Fetch: Doing timing memory access.\n"); + memReq->completionEvent = NULL; + + memReq->time = curTick; + + MemAccessResult result = icacheInterface->access(memReq); + + // If the cache missed (in this model functional and timing + // memories are different), then schedule an event to wake + // up this stage once the cache miss completes. + if (result != MA_HIT && icacheInterface->doEvents()) { + memReq->completionEvent = new CacheCompletionEvent(this); +// lastIcacheStall = curTick; + + // How does current model work as far as individual + // stages scheduling/unscheduling? + // Perhaps have only the main CPU scheduled/unscheduled, + // and have it choose what stages to run appropriately. + + DPRINTF(Fetch, "Fetch: Stalling due to icache miss.\n"); + _status = IcacheMissStall; + } + } + + return fault; +} + +template <class Impl> +inline void +SimpleFetch<Impl>::doSquash(const Addr &new_PC) +{ + DPRINTF(Fetch, "Fetch: Squashing, setting PC to: %#x.\n", new_PC); + + cpu->setNextPC(new_PC + instSize); + cpu->setPC(new_PC); + + // Clear the icache miss if it's outstanding. + if (_status == IcacheMissStall && icacheInterface) { + DPRINTF(Fetch, "Fetch: Squashing outstanding Icache miss.\n"); + // @todo: Use an actual thread number here. + icacheInterface->squash(0); + } + + _status = Squashing; + + ++fetchSquashCycles; +} + +template<class Impl> +void +SimpleFetch<Impl>::squashFromDecode(const Addr &new_PC, + const InstSeqNum &seq_num) +{ + DPRINTF(Fetch, "Fetch: Squashing from decode.\n"); + + doSquash(new_PC); + + // Tell the CPU to remove any instructions that are in flight between + // fetch and decode. + cpu->removeInstsUntil(seq_num); + +} + +template <class Impl> +void +SimpleFetch<Impl>::squash(const Addr &new_PC) +{ + DPRINTF(Fetch, "Fetch: Squash from commit.\n"); + + doSquash(new_PC); + + // Tell the CPU to remove any instructions that are not in the ROB. + cpu->removeInstsNotInROB(); +} + +template<class Impl> +void +SimpleFetch<Impl>::tick() +{ + // Check squash signals from commit. + if (fromCommit->commitInfo.squash) { + DPRINTF(Fetch, "Fetch: Squashing instructions due to squash " + "from commit.\n"); + + // In any case, squash. + squash(fromCommit->commitInfo.nextPC); + + // Also check if there's a mispredict that happened. + if (fromCommit->commitInfo.branchMispredict) { + branchPred.squash(fromCommit->commitInfo.doneSeqNum, + fromCommit->commitInfo.nextPC, + fromCommit->commitInfo.branchTaken); + } else { + branchPred.squash(fromCommit->commitInfo.doneSeqNum); + } + + return; + } else if (fromCommit->commitInfo.doneSeqNum) { + // Update the branch predictor if it wasn't a squashed instruction + // that was braodcasted. + branchPred.update(fromCommit->commitInfo.doneSeqNum); + } + + // Check ROB squash signals from commit. + if (fromCommit->commitInfo.robSquashing) { + DPRINTF(Fetch, "Fetch: ROB is still squashing.\n"); + + // Continue to squash. + _status = Squashing; + + ++fetchSquashCycles; + return; + } + + // Check squash signals from decode. + if (fromDecode->decodeInfo.squash) { + DPRINTF(Fetch, "Fetch: Squashing instructions due to squash " + "from decode.\n"); + + // Update the branch predictor. + if (fromDecode->decodeInfo.branchMispredict) { + branchPred.squash(fromDecode->decodeInfo.doneSeqNum, + fromDecode->decodeInfo.nextPC, + fromDecode->decodeInfo.branchTaken); + } else { + branchPred.squash(fromDecode->decodeInfo.doneSeqNum); + } + + if (_status != Squashing) { + // Squash unless we're already squashing? + squashFromDecode(fromDecode->decodeInfo.nextPC, + fromDecode->decodeInfo.doneSeqNum); + return; + } + } + + // Check if any of the stall signals are high. + if (fromDecode->decodeInfo.stall || + fromRename->renameInfo.stall || + fromIEW->iewInfo.stall || + fromCommit->commitInfo.stall) + { + // Block stage, regardless of current status. + + DPRINTF(Fetch, "Fetch: Stalling stage.\n"); + DPRINTF(Fetch, "Fetch: Statuses: Decode: %i Rename: %i IEW: %i " + "Commit: %i\n", + fromDecode->decodeInfo.stall, + fromRename->renameInfo.stall, + fromIEW->iewInfo.stall, + fromCommit->commitInfo.stall); + + _status = Blocked; + + ++fetchBlockedCycles; + return; + } else if (_status == Blocked) { + // Unblock stage if status is currently blocked and none of the + // stall signals are being held high. + _status = Running; + + ++fetchBlockedCycles; + return; + } + + // If fetch has reached this point, then there are no squash signals + // still being held high. Check if fetch is in the squashing state; + // if so, fetch can switch to running. + // Similarly, there are no blocked signals still being held high. + // Check if fetch is in the blocked state; if so, fetch can switch to + // running. + if (_status == Squashing) { + DPRINTF(Fetch, "Fetch: Done squashing, switching to running.\n"); + + // Switch status to running + _status = Running; + + ++fetchSquashCycles; + } else if (_status != IcacheMissStall) { + DPRINTF(Fetch, "Fetch: Running stage.\n"); + + ++fetchCycles; + + fetch(); + } +} + +template<class Impl> +void +SimpleFetch<Impl>::fetch() +{ + ////////////////////////////////////////// + // Start actual fetch + ////////////////////////////////////////// + + // The current PC. + Addr fetch_PC = cpu->readPC(); + + // Fault code for memory access. + Fault fault = No_Fault; + + // If returning from the delay of a cache miss, then update the status + // to running, otherwise do the cache access. Possibly move this up + // to tick() function. + if (_status == IcacheMissComplete) { + DPRINTF(Fetch, "Fetch: Icache miss is complete.\n"); + + // Reset the completion event to NULL. + memReq->completionEvent = NULL; + + _status = Running; + } else { + DPRINTF(Fetch, "Fetch: Attempting to translate and read " + "instruction, starting at PC %08p.\n", + fetch_PC); + + fault = fetchCacheLine(fetch_PC); + } + + // If we had a stall due to an icache miss, then return. It'd + // be nicer if this were handled through the kind of fault that + // is returned by the function. + if (_status == IcacheMissStall) { + return; + } + + // As far as timing goes, the CPU will need to send an event through + // the MemReq in order to be woken up once the memory access completes. + // Probably have a status on a per thread basis so each thread can + // block independently and be woken up independently. + + Addr next_PC = fetch_PC; + InstSeqNum inst_seq; + MachInst inst; + unsigned offset = fetch_PC & cacheBlkMask; + unsigned fetched; + + if (fault == No_Fault) { + // If the read of the first instruction was successful, then grab the + // instructions from the rest of the cache line and put them into the + // queue heading to decode. + + DPRINTF(Fetch, "Fetch: Adding instructions to queue to decode.\n"); + + ////////////////////////// + // Fetch first instruction + ////////////////////////// + + // Need to keep track of whether or not a predicted branch + // ended this fetch block. + bool predicted_branch = false; + + for (fetched = 0; + offset < cacheBlkSize && + fetched < fetchWidth && + !predicted_branch; + ++fetched) + { + + // Get a sequence number. + inst_seq = cpu->getAndIncrementInstSeq(); + + // Make sure this is a valid index. + assert(offset <= cacheBlkSize - instSize); + + // Get the instruction from the array of the cache line. + inst = htoa(*reinterpret_cast<MachInst *> + (&cacheData[offset])); + + // Create a new DynInst from the instruction fetched. + DynInstPtr instruction = new DynInst(inst, fetch_PC, next_PC, + inst_seq, cpu); + + DPRINTF(Fetch, "Fetch: Instruction %i created, with PC %#x\n", + inst_seq, instruction->readPC()); + + DPRINTF(Fetch, "Fetch: Instruction opcode is: %03p\n", + OPCODE(inst)); + + instruction->traceData = + Trace::getInstRecord(curTick, cpu->xcBase(), cpu, + instruction->staticInst, + instruction->readPC(), 0); + + predicted_branch = lookupAndUpdateNextPC(instruction, next_PC); + + // Add instruction to the CPU's list of instructions. + cpu->addInst(instruction); + + // Write the instruction to the first slot in the queue + // that heads to decode. + toDecode->insts[fetched] = instruction; + + toDecode->size++; + + // Increment stat of fetched instructions. + ++fetchedInsts; + + // Move to the next instruction, unless we have a branch. + fetch_PC = next_PC; + + offset+= instSize; + } + + fetch_nisn_dist.sample(fetched); + } + + // Now that fetching is completed, update the PC to signify what the next + // cycle will be. Might want to move this to the beginning of this + // function so that the PC updates at the beginning of everything. + // Or might want to leave setting the PC to the main CPU, with fetch + // only changing the nextPC (will require correct determination of + // next PC). + if (fault == No_Fault) { + DPRINTF(Fetch, "Fetch: Setting PC to %08p.\n", next_PC); + cpu->setPC(next_PC); + cpu->setNextPC(next_PC + instSize); + } else { + // If the issue was an icache miss, then we can just return and + // wait until it is handled. + if (_status == IcacheMissStall) { + return; + } + + // Handle the fault. + // This stage will not be able to continue until all the ROB + // slots are empty, at which point the fault can be handled. + // The only other way it can wake up is if a squash comes along + // and changes the PC. Not sure how to handle that case...perhaps + // have it handled by the upper level CPU class which peeks into the + // time buffer and sees if a squash comes along, in which case it + // changes the status. + + DPRINTF(Fetch, "Fetch: Blocked, need to handle the trap.\n"); + + _status = Blocked; +#ifdef FULL_SYSTEM +// cpu->trap(fault); + // Send a signal to the ROB indicating that there's a trap from the + // fetch stage that needs to be handled. Need to indicate that + // there's a fault, and the fault type. +#else // !FULL_SYSTEM + fatal("fault (%d) detected @ PC %08p", fault, cpu->readPC()); +#endif // FULL_SYSTEM + } +} |