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gem5/cpu/o3/fetch_impl.hh
Kevin Lim a514bf2150 Comments and code cleanup. 
cpu/activity.cc:
cpu/activity.hh:
cpu/o3/alpha_cpu.hh:
    Updates to include comments.
cpu/base_dyn_inst.cc:
    Remove call to thread->misspeculating(), as it's never actually misspeculating.

--HG--
extra : convert_revision : 86574d684770fac9b480475acca048ea418cdac3
2006-05-31 11:45:02 -04:00

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/*
* Copyright (c) 2004-2006 The Regents of The University of Michigan
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions are
* met: redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer;
* redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution;
* neither the name of the copyright holders nor the names of its
* contributors may be used to endorse or promote products derived from
* this software without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
* A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
* OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
* SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
* LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
* DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
* THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
* OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/
#include "arch/isa_traits.hh"
#include "cpu/exetrace.hh"
#include "cpu/o3/fetch.hh"
#include "mem/base_mem.hh"
#include "mem/mem_interface.hh"
#include "mem/mem_req.hh"
#include "sim/byteswap.hh"
#include "sim/root.hh"
#if FULL_SYSTEM
#include "arch/tlb.hh"
#include "arch/vtophys.hh"
#include "base/remote_gdb.hh"
#include "mem/functional/memory_control.hh"
#include "mem/functional/physical.hh"
#include "sim/system.hh"
#else // !FULL_SYSTEM
#include "mem/functional/functional.hh"
#endif // FULL_SYSTEM
#include <algorithm>
using namespace std;
template<class Impl>
DefaultFetch<Impl>::CacheCompletionEvent::CacheCompletionEvent(MemReqPtr &_req,
DefaultFetch *_fetch)
: Event(&mainEventQueue, Delayed_Writeback_Pri),
req(_req),
fetch(_fetch)
{
this->setFlags(Event::AutoDelete);
}
template<class Impl>
void
DefaultFetch<Impl>::CacheCompletionEvent::process()
{
fetch->processCacheCompletion(req);
}
template<class Impl>
const char *
DefaultFetch<Impl>::CacheCompletionEvent::description()
{
return "DefaultFetch cache completion event";
}
template<class Impl>
DefaultFetch<Impl>::DefaultFetch(Params *params)
: icacheInterface(params->icacheInterface),
branchPred(params),
decodeToFetchDelay(params->decodeToFetchDelay),
renameToFetchDelay(params->renameToFetchDelay),
iewToFetchDelay(params->iewToFetchDelay),
commitToFetchDelay(params->commitToFetchDelay),
fetchWidth(params->fetchWidth),
numThreads(params->numberOfThreads),
numFetchingThreads(params->smtNumFetchingThreads),
interruptPending(false)
{
if (numThreads > Impl::MaxThreads)
fatal("numThreads is not a valid value\n");
DPRINTF(Fetch, "Fetch constructor called\n");
// Set fetch stage's status to inactive.
_status = Inactive;
string policy = params->smtFetchPolicy;
// Convert string to lowercase
std::transform(policy.begin(), policy.end(), policy.begin(),
(int(*)(int)) tolower);
// Figure out fetch policy
if (policy == "singlethread") {
fetchPolicy = SingleThread;
} else if (policy == "roundrobin") {
fetchPolicy = RoundRobin;
DPRINTF(Fetch, "Fetch policy set to Round Robin\n");
} else if (policy == "branch") {
fetchPolicy = Branch;
DPRINTF(Fetch, "Fetch policy set to Branch Count\n");
} else if (policy == "iqcount") {
fetchPolicy = IQ;
DPRINTF(Fetch, "Fetch policy set to IQ count\n");
} else if (policy == "lsqcount") {
fetchPolicy = LSQ;
DPRINTF(Fetch, "Fetch policy set to LSQ count\n");
} else {
fatal("Invalid Fetch Policy. Options Are: {SingleThread,"
" RoundRobin,LSQcount,IQcount}\n");
}
// Size of cache block.
cacheBlkSize = icacheInterface ? icacheInterface->getBlockSize() : 64;
// Create mask to get rid of offset bits.
cacheBlkMask = (cacheBlkSize - 1);
for (int tid=0; tid < numThreads; tid++) {
fetchStatus[tid] = Running;
priorityList.push_back(tid);
// Create a new memory request.
memReq[tid] = NULL;
// Create space to store a cache line.
cacheData[tid] = new uint8_t[cacheBlkSize];
stalls[tid].decode = 0;
stalls[tid].rename = 0;
stalls[tid].iew = 0;
stalls[tid].commit = 0;
}
// Get the size of an instruction.
instSize = sizeof(MachInst);
}
template <class Impl>
std::string
DefaultFetch<Impl>::name() const
{
return cpu->name() + ".fetch";
}
template <class Impl>
void
DefaultFetch<Impl>::regStats()
{
icacheStallCycles
.name(name() + ".icacheStallCycles")
.desc("Number of cycles fetch is stalled on an Icache miss")
.prereq(icacheStallCycles);
fetchedInsts
.name(name() + ".Insts")
.desc("Number of instructions fetch has processed")
.prereq(fetchedInsts);
fetchedBranches
.name(name() + ".Branches")
.desc("Number of branches that fetch encountered")
.prereq(fetchedBranches);
predictedBranches
.name(name() + ".predictedBranches")
.desc("Number of branches that fetch has predicted taken")
.prereq(predictedBranches);
fetchCycles
.name(name() + ".Cycles")
.desc("Number of cycles fetch has run and was not squashing or"
" blocked")
.prereq(fetchCycles);
fetchSquashCycles
.name(name() + ".SquashCycles")
.desc("Number of cycles fetch has spent squashing")
.prereq(fetchSquashCycles);
fetchIdleCycles
.name(name() + ".IdleCycles")
.desc("Number of cycles fetch was idle")
.prereq(fetchIdleCycles);
fetchBlockedCycles
.name(name() + ".BlockedCycles")
.desc("Number of cycles fetch has spent blocked")
.prereq(fetchBlockedCycles);
fetchedCacheLines
.name(name() + ".CacheLines")
.desc("Number of cache lines fetched")
.prereq(fetchedCacheLines);
fetchMiscStallCycles
.name(name() + ".MiscStallCycles")
.desc("Number of cycles fetch has spent waiting on interrupts, or "
"bad addresses, or out of MSHRs")
.prereq(fetchMiscStallCycles);
fetchIcacheSquashes
.name(name() + ".IcacheSquashes")
.desc("Number of outstanding Icache misses that were squashed")
.prereq(fetchIcacheSquashes);
fetchNisnDist
.init(/* base value */ 0,
/* last value */ fetchWidth,
/* bucket size */ 1)
.name(name() + ".rateDist")
.desc("Number of instructions fetched each cycle (Total)")
.flags(Stats::pdf);
idleRate
.name(name() + ".idleRate")
.desc("Percent of cycles fetch was idle")
.prereq(idleRate);
idleRate = fetchIdleCycles * 100 / cpu->numCycles;
branchRate
.name(name() + ".branchRate")
.desc("Number of branch fetches per cycle")
.flags(Stats::total);
branchRate = fetchedBranches / cpu->numCycles;
fetchRate
.name(name() + ".rate")
.desc("Number of inst fetches per cycle")
.flags(Stats::total);
fetchRate = fetchedInsts / cpu->numCycles;
branchPred.regStats();
}
template<class Impl>
void
DefaultFetch<Impl>::setCPU(FullCPU *cpu_ptr)
{
DPRINTF(Fetch, "Setting the CPU pointer.\n");
cpu = cpu_ptr;
// Fetch needs to start fetching instructions at the very beginning,
// so it must start up in active state.
switchToActive();
}
template<class Impl>
void
DefaultFetch<Impl>::setTimeBuffer(TimeBuffer<TimeStruct> *time_buffer)
{
DPRINTF(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
DefaultFetch<Impl>::setActiveThreads(list<unsigned> *at_ptr)
{
DPRINTF(Fetch, "Setting active threads list pointer.\n");
activeThreads = at_ptr;
}
template<class Impl>
void
DefaultFetch<Impl>::setFetchQueue(TimeBuffer<FetchStruct> *fq_ptr)
{
DPRINTF(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);
}
#if 0
template<class Impl>
void
DefaultFetch<Impl>::setPageTable(PageTable *pt_ptr)
{
DPRINTF(Fetch, "Setting the page table pointer.\n");
#if !FULL_SYSTEM
pTable = pt_ptr;
#endif
}
#endif
template<class Impl>
void
DefaultFetch<Impl>::initStage()
{
// Setup PC and nextPC with initial state.
for (int tid = 0; tid < numThreads; tid++) {
PC[tid] = cpu->readPC(tid);
nextPC[tid] = cpu->readNextPC(tid);
}
}
template<class Impl>
void
DefaultFetch<Impl>::processCacheCompletion(MemReqPtr &req)
{
unsigned tid = req->thread_num;
DPRINTF(Fetch, "[tid:%u] Waking up from cache miss.\n",tid);
// Only change the status if it's still waiting on the icache access
// to return.
if (fetchStatus[tid] != IcacheMissStall ||
req != memReq[tid] ||
isSwitchedOut()) {
++fetchIcacheSquashes;
return;
}
// Wake up the CPU (if it went to sleep and was waiting on this completion
// event).
cpu->wakeCPU();
DPRINTF(Activity, "[tid:%u] Activating fetch due to cache completion\n",
tid);
switchToActive();
// Only switch to IcacheMissComplete if we're not stalled as well.
if (checkStall(tid)) {
fetchStatus[tid] = Blocked;
} else {
fetchStatus[tid] = IcacheMissComplete;
}
// memcpy(cacheData[tid], memReq[tid]->data, memReq[tid]->size);
// Reset the mem req to NULL.
memReq[tid] = NULL;
}
template <class Impl>
void
DefaultFetch<Impl>::switchOut()
{
// Fetch is ready to switch out at any time.
switchedOut = true;
cpu->signalSwitched();
}
template <class Impl>
void
DefaultFetch<Impl>::doSwitchOut()
{
// Branch predictor needs to have its state cleared.
branchPred.switchOut();
}
template <class Impl>
void
DefaultFetch<Impl>::takeOverFrom()
{
// Reset all state
for (int i = 0; i < Impl::MaxThreads; ++i) {
stalls[i].decode = 0;
stalls[i].rename = 0;
stalls[i].iew = 0;
stalls[i].commit = 0;
PC[i] = cpu->readPC(i);
nextPC[i] = cpu->readNextPC(i);
fetchStatus[i] = Running;
}
numInst = 0;
wroteToTimeBuffer = false;
_status = Inactive;
switchedOut = false;
branchPred.takeOverFrom();
}
template <class Impl>
void
DefaultFetch<Impl>::wakeFromQuiesce()
{
DPRINTF(Fetch, "Waking up from quiesce\n");
// Hopefully this is safe
// @todo: Allow other threads to wake from quiesce.
fetchStatus[0] = Running;
}
template <class Impl>
inline void
DefaultFetch<Impl>::switchToActive()
{
if (_status == Inactive) {
DPRINTF(Activity, "Activating stage.\n");
cpu->activateStage(FullCPU::FetchIdx);
_status = Active;
}
}
template <class Impl>
inline void
DefaultFetch<Impl>::switchToInactive()
{
if (_status == Active) {
DPRINTF(Activity, "Deactivating stage.\n");
cpu->deactivateStage(FullCPU::FetchIdx);
_status = Inactive;
}
}
template <class Impl>
bool
DefaultFetch<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, inst->threadNumber);
++fetchedBranches;
if (predict_taken) {
++predictedBranches;
}
return predict_taken;
}
template <class Impl>
bool
DefaultFetch<Impl>::fetchCacheLine(Addr fetch_PC, Fault &ret_fault, unsigned tid)
{
Fault fault = NoFault;
#if FULL_SYSTEM
// Flag to say whether or not address is physical addr.
unsigned flags = cpu->inPalMode(fetch_PC) ? PHYSICAL : 0;
#else
unsigned flags = 0;
#endif // FULL_SYSTEM
if (interruptPending && flags == 0 || switchedOut) {
// Hold off fetch from getting new instructions while an interrupt
// is pending.
return false;
}
// 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 instruction's address.
// Set the appropriate read size and flags as well.
memReq[tid] = new MemReq();
memReq[tid]->asid = tid;
memReq[tid]->thread_num = tid;
memReq[tid]->data = new uint8_t[64];
memReq[tid]->xc = cpu->xcBase(tid);
memReq[tid]->cmd = Read;
memReq[tid]->reset(fetch_PC, cacheBlkSize, flags);
// Translate the instruction request.
//#if FULL_SYSTEM
fault = cpu->translateInstReq(memReq[tid]);
//#else
// fault = pTable->translate(memReq[tid]);
//#endif
// In the case of faults, the fetch stage may need to stall and wait
// for the ITB miss to be handled.
// If translation was successful, attempt to read the first
// instruction.
if (fault == NoFault) {
#if FULL_SYSTEM
if (cpu->system->memctrl->badaddr(memReq[tid]->paddr) ||
memReq[tid]->flags & UNCACHEABLE) {
DPRINTF(Fetch, "Fetch: Bad address %#x (hopefully on a "
"misspeculating path)!",
memReq[tid]->paddr);
ret_fault = TheISA::genMachineCheckFault();
return false;
}
#endif
DPRINTF(Fetch, "Fetch: Doing instruction read.\n");
fault = cpu->mem->read(memReq[tid], cacheData[tid]);
// This read may change when the mem interface changes.
// Now do the timing access to see whether or not the instruction
// exists within the cache.
if (icacheInterface && !icacheInterface->isBlocked()) {
DPRINTF(Fetch, "Doing cache access.\n");
memReq[tid]->completionEvent = NULL;
memReq[tid]->time = curTick;
MemAccessResult result = icacheInterface->access(memReq[tid]);
fetchedCacheLines++;
// If the cache missed, then schedule an event to wake
// up this stage once the cache miss completes.
// @todo: Possibly allow for longer than 1 cycle cache hits.
if (result != MA_HIT && icacheInterface->doEvents()) {
memReq[tid]->completionEvent =
new CacheCompletionEvent(memReq[tid], this);
lastIcacheStall[tid] = curTick;
DPRINTF(Activity, "[tid:%i]: Activity: Stalling due to I-cache "
"miss.\n", tid);
fetchStatus[tid] = IcacheMissStall;
} else {
DPRINTF(Fetch, "[tid:%i]: I-Cache hit. Doing Instruction "
"read.\n", tid);
// memcpy(cacheData[tid], memReq[tid]->data, memReq[tid]->size);
}
} else {
DPRINTF(Fetch, "[tid:%i] Out of MSHRs!\n", tid);
ret_fault = NoFault;
return false;
}
}
ret_fault = fault;
return true;
}
template <class Impl>
inline void
DefaultFetch<Impl>::doSquash(const Addr &new_PC, unsigned tid)
{
DPRINTF(Fetch, "[tid:%i]: Squashing, setting PC to: %#x.\n",
tid, new_PC);
PC[tid] = new_PC;
nextPC[tid] = new_PC + instSize;
// Clear the icache miss if it's outstanding.
if (fetchStatus[tid] == IcacheMissStall && icacheInterface) {
DPRINTF(Fetch, "[tid:%i]: Squashing outstanding Icache miss.\n",
tid);
memReq[tid] = NULL;
}
fetchStatus[tid] = Squashing;
++fetchSquashCycles;
}
template<class Impl>
void
DefaultFetch<Impl>::squashFromDecode(const Addr &new_PC,
const InstSeqNum &seq_num,
unsigned tid)
{
DPRINTF(Fetch, "[tid:%i]: Squashing from decode.\n",tid);
doSquash(new_PC, tid);
// Tell the CPU to remove any instructions that are in flight between
// fetch and decode.
cpu->removeInstsUntil(seq_num, tid);
}
template<class Impl>
bool
DefaultFetch<Impl>::checkStall(unsigned tid) const
{
bool ret_val = false;
if (cpu->contextSwitch) {
DPRINTF(Fetch,"[tid:%i]: Stalling for a context switch.\n",tid);
ret_val = true;
} else if (stalls[tid].decode) {
DPRINTF(Fetch,"[tid:%i]: Stall from Decode stage detected.\n",tid);
ret_val = true;
} else if (stalls[tid].rename) {
DPRINTF(Fetch,"[tid:%i]: Stall from Rename stage detected.\n",tid);
ret_val = true;
} else if (stalls[tid].iew) {
DPRINTF(Fetch,"[tid:%i]: Stall from IEW stage detected.\n",tid);
ret_val = true;
} else if (stalls[tid].commit) {
DPRINTF(Fetch,"[tid:%i]: Stall from Commit stage detected.\n",tid);
ret_val = true;
}
return ret_val;
}
template<class Impl>
typename DefaultFetch<Impl>::FetchStatus
DefaultFetch<Impl>::updateFetchStatus()
{
//Check Running
list<unsigned>::iterator threads = (*activeThreads).begin();
while (threads != (*activeThreads).end()) {
unsigned tid = *threads++;
if (fetchStatus[tid] == Running ||
fetchStatus[tid] == Squashing ||
fetchStatus[tid] == IcacheMissComplete) {
if (_status == Inactive) {
DPRINTF(Activity, "[tid:%i]: Activating stage.\n",tid);
if (fetchStatus[tid] == IcacheMissComplete) {
DPRINTF(Activity, "[tid:%i]: Activating fetch due to cache"
"completion\n",tid);
}
cpu->activateStage(FullCPU::FetchIdx);
}
return Active;
}
}
// Stage is switching from active to inactive, notify CPU of it.
if (_status == Active) {
DPRINTF(Activity, "Deactivating stage.\n");
cpu->deactivateStage(FullCPU::FetchIdx);
}
return Inactive;
}
template <class Impl>
void
DefaultFetch<Impl>::squash(const Addr &new_PC, unsigned tid)
{
DPRINTF(Fetch, "[tid:%u]: Squash from commit.\n",tid);
doSquash(new_PC, tid);
// Tell the CPU to remove any instructions that are not in the ROB.
cpu->removeInstsNotInROB(tid);
}
template <class Impl>
void
DefaultFetch<Impl>::tick()
{
list<unsigned>::iterator threads = (*activeThreads).begin();
bool status_change = false;
wroteToTimeBuffer = false;
while (threads != (*activeThreads).end()) {
unsigned tid = *threads++;
// Check the signals for each thread to determine the proper status
// for each thread.
bool updated_status = checkSignalsAndUpdate(tid);
status_change = status_change || updated_status;
}
DPRINTF(Fetch, "Running stage.\n");
// Reset the number of the instruction we're fetching.
numInst = 0;
if (fromCommit->commitInfo[0].interruptPending) {
interruptPending = true;
}
if (fromCommit->commitInfo[0].clearInterrupt) {
interruptPending = false;
}
for (threadFetched = 0; threadFetched < numFetchingThreads;
threadFetched++) {
// Fetch each of the actively fetching threads.
fetch(status_change);
}
// Record number of instructions fetched this cycle for distribution.
fetchNisnDist.sample(numInst);
if (status_change) {
// Change the fetch stage status if there was a status change.
_status = updateFetchStatus();
}
// If there was activity this cycle, inform the CPU of it.
if (wroteToTimeBuffer || cpu->contextSwitch) {
DPRINTF(Activity, "Activity this cycle.\n");
cpu->activityThisCycle();
}
}
template <class Impl>
bool
DefaultFetch<Impl>::checkSignalsAndUpdate(unsigned tid)
{
// Update the per thread stall statuses.
if (fromDecode->decodeBlock[tid]) {
stalls[tid].decode = true;
}
if (fromDecode->decodeUnblock[tid]) {
assert(stalls[tid].decode);
assert(!fromDecode->decodeBlock[tid]);
stalls[tid].decode = false;
}
if (fromRename->renameBlock[tid]) {
stalls[tid].rename = true;
}
if (fromRename->renameUnblock[tid]) {
assert(stalls[tid].rename);
assert(!fromRename->renameBlock[tid]);
stalls[tid].rename = false;
}
if (fromIEW->iewBlock[tid]) {
stalls[tid].iew = true;
}
if (fromIEW->iewUnblock[tid]) {
assert(stalls[tid].iew);
assert(!fromIEW->iewBlock[tid]);
stalls[tid].iew = false;
}
if (fromCommit->commitBlock[tid]) {
stalls[tid].commit = true;
}
if (fromCommit->commitUnblock[tid]) {
assert(stalls[tid].commit);
assert(!fromCommit->commitBlock[tid]);
stalls[tid].commit = false;
}
// Check squash signals from commit.
if (fromCommit->commitInfo[tid].squash) {
DPRINTF(Fetch, "[tid:%u]: Squashing instructions due to squash "
"from commit.\n",tid);
// In any case, squash.
squash(fromCommit->commitInfo[tid].nextPC,tid);
// Also check if there's a mispredict that happened.
if (fromCommit->commitInfo[tid].branchMispredict) {
branchPred.squash(fromCommit->commitInfo[tid].doneSeqNum,
fromCommit->commitInfo[tid].nextPC,
fromCommit->commitInfo[tid].branchTaken,
tid);
} else {
branchPred.squash(fromCommit->commitInfo[tid].doneSeqNum,
tid);
}
return true;
} else if (fromCommit->commitInfo[tid].doneSeqNum) {
// Update the branch predictor if it wasn't a squashed instruction
// that was broadcasted.
branchPred.update(fromCommit->commitInfo[tid].doneSeqNum, tid);
}
// Check ROB squash signals from commit.
if (fromCommit->commitInfo[tid].robSquashing) {
DPRINTF(Fetch, "[tid:%u]: ROB is still squashing Thread %u.\n", tid);
// Continue to squash.
fetchStatus[tid] = Squashing;
return true;
}
// Check squash signals from decode.
if (fromDecode->decodeInfo[tid].squash) {
DPRINTF(Fetch, "[tid:%u]: Squashing instructions due to squash "
"from decode.\n",tid);
// Update the branch predictor.
if (fromDecode->decodeInfo[tid].branchMispredict) {
branchPred.squash(fromDecode->decodeInfo[tid].doneSeqNum,
fromDecode->decodeInfo[tid].nextPC,
fromDecode->decodeInfo[tid].branchTaken,
tid);
} else {
branchPred.squash(fromDecode->decodeInfo[tid].doneSeqNum,
tid);
}
if (fetchStatus[tid] != Squashing) {
// Squash unless we're already squashing
squashFromDecode(fromDecode->decodeInfo[tid].nextPC,
fromDecode->decodeInfo[tid].doneSeqNum,
tid);
return true;
}
}
if (fetchStatus[tid] != IcacheMissStall && checkStall(tid)) {
DPRINTF(Fetch, "[tid:%i]: Setting to blocked\n",tid);
fetchStatus[tid] = Blocked;
return true;
}
if (fetchStatus[tid] == Blocked ||
fetchStatus[tid] == Squashing) {
// Switch status to running if fetch isn't being told to block or
// squash this cycle.
DPRINTF(Fetch, "[tid:%i]: Done squashing, switching to running.\n",
tid);
fetchStatus[tid] = Running;
return true;
}
// If we've reached this point, we have not gotten any signals that
// cause fetch to change its status. Fetch remains the same as before.
return false;
}
template<class Impl>
void
DefaultFetch<Impl>::fetch(bool &status_change)
{
//////////////////////////////////////////
// Start actual fetch
//////////////////////////////////////////
int tid = getFetchingThread(fetchPolicy);
if (tid == -1) {
DPRINTF(Fetch,"There are no more threads available to fetch from.\n");
// Breaks looping condition in tick()
threadFetched = numFetchingThreads;
return;
}
// The current PC.
Addr &fetch_PC = PC[tid];
// Fault code for memory access.
Fault fault = NoFault;
// 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 (fetchStatus[tid] == IcacheMissComplete) {
DPRINTF(Fetch, "[tid:%i]: Icache miss is complete.\n",
tid);
fetchStatus[tid] = Running;
status_change = true;
} else if (fetchStatus[tid] == Running) {
DPRINTF(Fetch, "[tid:%i]: Attempting to translate and read "
"instruction, starting at PC %08p.\n",
tid, fetch_PC);
bool fetch_success = fetchCacheLine(fetch_PC, fault, tid);
if (!fetch_success) {
++fetchMiscStallCycles;
return;
}
} else {
if (fetchStatus[tid] == Idle) {
++fetchIdleCycles;
} else if (fetchStatus[tid] == Blocked) {
++fetchBlockedCycles;
} else if (fetchStatus[tid] == Squashing) {
++fetchSquashCycles;
} else if (fetchStatus[tid] == IcacheMissStall) {
++icacheStallCycles;
}
// Status is Idle, Squashing, Blocked, or IcacheMissStall, so
// fetch should do nothing.
return;
}
++fetchCycles;
// If we had a stall due to an icache miss, then return.
if (fetchStatus[tid] == IcacheMissStall) {
++icacheStallCycles;
status_change = true;
return;
}
Addr next_PC = fetch_PC;
InstSeqNum inst_seq;
MachInst inst;
ExtMachInst ext_inst;
// @todo: Fix this hack.
unsigned offset = (fetch_PC & cacheBlkMask) & ~3;
if (fault == NoFault) {
// 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, "[tid:%i]: Adding instructions to queue to "
"decode.\n",tid);
// Need to keep track of whether or not a predicted branch
// ended this fetch block.
bool predicted_branch = false;
for (;
offset < cacheBlkSize &&
numInst < fetchWidth &&
!predicted_branch;
++numInst) {
// 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 = gtoh(*reinterpret_cast<MachInst *>
(&cacheData[tid][offset]));
ext_inst = TheISA::makeExtMI(inst, fetch_PC);
// Create a new DynInst from the instruction fetched.
DynInstPtr instruction = new DynInst(ext_inst, fetch_PC,
next_PC,
inst_seq, cpu);
instruction->setThread(tid);
instruction->setASID(tid);
instruction->setState(cpu->thread[tid]);
DPRINTF(Fetch, "[tid:%i]: Instruction PC %#x created "
"[sn:%lli]\n",
tid, instruction->readPC(), inst_seq);
DPRINTF(Fetch, "[tid:%i]: Instruction is: %s\n",
tid, instruction->staticInst->disassemble(fetch_PC));
instruction->traceData =
Trace::getInstRecord(curTick, cpu->xcBase(tid), cpu,
instruction->staticInst,
instruction->readPC(),tid);
predicted_branch = lookupAndUpdateNextPC(instruction, next_PC);
// Add instruction to the CPU's list of instructions.
instruction->setInstListIt(cpu->addInst(instruction));
// Write the instruction to the first slot in the queue
// that heads to decode.
toDecode->insts[numInst] = instruction;
toDecode->size++;
// Increment stat of fetched instructions.
++fetchedInsts;
// Move to the next instruction, unless we have a branch.
fetch_PC = next_PC;
if (instruction->isQuiesce()) {
warn("%lli: Quiesce instruction encountered, halting fetch!",
curTick);
fetchStatus[tid] = QuiescePending;
++numInst;
status_change = true;
break;
}
offset+= instSize;
}
}
if (numInst > 0) {
wroteToTimeBuffer = true;
}
// Now that fetching is completed, update the PC to signify what the next
// cycle will be.
if (fault == NoFault) {
DPRINTF(Fetch, "[tid:%i]: Setting PC to %08p.\n",tid, next_PC);
PC[tid] = next_PC;
nextPC[tid] = next_PC + instSize;
} else {
// We shouldn't be in an icache miss and also have a fault (an ITB
// miss)
if (fetchStatus[tid] == IcacheMissStall) {
panic("Fetch should have exited prior to this!");
}
// Send the fault to commit. This thread will not do anything
// until commit handles the fault. The only other way it can
// wake up is if a squash comes along and changes the PC.
#if FULL_SYSTEM
assert(numInst != fetchWidth);
// Get a sequence number.
inst_seq = cpu->getAndIncrementInstSeq();
// We will use a nop in order to carry the fault.
ext_inst = TheISA::NoopMachInst;
// Create a new DynInst from the dummy nop.
DynInstPtr instruction = new DynInst(ext_inst, fetch_PC,
next_PC,
inst_seq, cpu);
instruction->setPredTarg(next_PC + instSize);
instruction->setThread(tid);
instruction->setASID(tid);
instruction->setState(cpu->thread[tid]);
instruction->traceData = NULL;
instruction->setInstListIt(cpu->addInst(instruction));
instruction->fault = fault;
toDecode->insts[numInst] = instruction;
toDecode->size++;
DPRINTF(Fetch, "[tid:%i]: Blocked, need to handle the trap.\n",tid);
fetchStatus[tid] = TrapPending;
status_change = true;
warn("%lli fault (%d) detected @ PC %08p", curTick, fault, PC[tid]);
#else // !FULL_SYSTEM
fatal("fault (%d) detected @ PC %08p", fault, PC[tid]);
#endif // FULL_SYSTEM
}
}
///////////////////////////////////////
// //
// SMT FETCH POLICY MAINTAINED HERE //
// //
///////////////////////////////////////
template<class Impl>
int
DefaultFetch<Impl>::getFetchingThread(FetchPriority &fetch_priority)
{
if (numThreads > 1) {
switch (fetch_priority) {
case SingleThread:
return 0;
case RoundRobin:
return roundRobin();
case IQ:
return iqCount();
case LSQ:
return lsqCount();
case Branch:
return branchCount();
default:
return -1;
}
} else {
int tid = *((*activeThreads).begin());
if (fetchStatus[tid] == Running ||
fetchStatus[tid] == IcacheMissComplete ||
fetchStatus[tid] == Idle) {
return tid;
} else {
return -1;
}
}
}
template<class Impl>
int
DefaultFetch<Impl>::roundRobin()
{
list<unsigned>::iterator pri_iter = priorityList.begin();
list<unsigned>::iterator end = priorityList.end();
int high_pri;
while (pri_iter != end) {
high_pri = *pri_iter;
assert(high_pri <= numThreads);
if (fetchStatus[high_pri] == Running ||
fetchStatus[high_pri] == IcacheMissComplete ||
fetchStatus[high_pri] == Idle) {
priorityList.erase(pri_iter);
priorityList.push_back(high_pri);
return high_pri;
}
pri_iter++;
}
return -1;
}
template<class Impl>
int
DefaultFetch<Impl>::iqCount()
{
priority_queue<unsigned> PQ;
list<unsigned>::iterator threads = (*activeThreads).begin();
while (threads != (*activeThreads).end()) {
unsigned tid = *threads++;
PQ.push(fromIEW->iewInfo[tid].iqCount);
}
while (!PQ.empty()) {
unsigned high_pri = PQ.top();
if (fetchStatus[high_pri] == Running ||
fetchStatus[high_pri] == IcacheMissComplete ||
fetchStatus[high_pri] == Idle)
return high_pri;
else
PQ.pop();
}
return -1;
}
template<class Impl>
int
DefaultFetch<Impl>::lsqCount()
{
priority_queue<unsigned> PQ;
list<unsigned>::iterator threads = (*activeThreads).begin();
while (threads != (*activeThreads).end()) {
unsigned tid = *threads++;
PQ.push(fromIEW->iewInfo[tid].ldstqCount);
}
while (!PQ.empty()) {
unsigned high_pri = PQ.top();
if (fetchStatus[high_pri] == Running ||
fetchStatus[high_pri] == IcacheMissComplete ||
fetchStatus[high_pri] == Idle)
return high_pri;
else
PQ.pop();
}
return -1;
}
template<class Impl>
int
DefaultFetch<Impl>::branchCount()
{
list<unsigned>::iterator threads = (*activeThreads).begin();
return *threads;
}
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