#include "base/trace.hh"
#include "cpu/o3/2bit_local_pred.hh"
-DefaultBP::DefaultBP(unsigned _localPredictorSize,
- unsigned _localCtrBits,
- unsigned _instShiftAmt)
+LocalBP::LocalBP(unsigned _localPredictorSize,
+ unsigned _localCtrBits,
+ unsigned _instShiftAmt)
: localPredictorSize(_localPredictorSize),
localCtrBits(_localCtrBits),
instShiftAmt(_instShiftAmt)
}
void
-DefaultBP::reset()
+LocalBP::reset()
{
for (int i = 0; i < localPredictorSets; ++i) {
localCtrs[i].reset();
}
bool
-DefaultBP::lookup(Addr &branch_addr)
+LocalBP::lookup(Addr &branch_addr, void * &bp_history)
{
bool taken;
- uint8_t local_prediction;
+ uint8_t counter_val;
unsigned local_predictor_idx = getLocalIndex(branch_addr);
DPRINTF(Fetch, "Branch predictor: Looking up index %#x\n",
local_predictor_idx);
- local_prediction = localCtrs[local_predictor_idx].read();
+ counter_val = localCtrs[local_predictor_idx].read();
DPRINTF(Fetch, "Branch predictor: prediction is %i.\n",
- (int)local_prediction);
+ (int)counter_val);
- taken = getPrediction(local_prediction);
+ taken = getPrediction(counter_val);
#if 0
// Speculative update.
}
void
-DefaultBP::update(Addr &branch_addr, bool taken)
+LocalBP::update(Addr &branch_addr, bool taken, void *bp_history)
{
+ assert(bp_history == NULL);
unsigned local_predictor_idx;
// Update the local predictor.
inline
bool
-DefaultBP::getPrediction(uint8_t &count)
+LocalBP::getPrediction(uint8_t &count)
{
// Get the MSB of the count
return (count >> (localCtrBits - 1));
inline
unsigned
-DefaultBP::getLocalIndex(Addr &branch_addr)
+LocalBP::getLocalIndex(Addr &branch_addr)
{
return (branch_addr >> instShiftAmt) & indexMask;
}
#include <vector>
-class DefaultBP
+/**
+ * Implements a local predictor that uses the PC to index into a table of
+ * counters. Note that any time a pointer to the bp_history is given, it
+ * should be NULL using this predictor because it does not have any branch
+ * predictor state that needs to be recorded or updated; the update can be
+ * determined solely by the branch being taken or not taken.
+ */
+class LocalBP
{
public:
/**
* @param localCtrBits Number of bits per counter.
* @param instShiftAmt Offset amount for instructions to ignore alignment.
*/
- DefaultBP(unsigned localPredictorSize, unsigned localCtrBits,
- unsigned instShiftAmt);
+ LocalBP(unsigned localPredictorSize, unsigned localCtrBits,
+ unsigned instShiftAmt);
/**
* Looks up the given address in the branch predictor and returns
* a true/false value as to whether it is taken.
* @param branch_addr The address of the branch to look up.
+ * @param bp_history Pointer to any bp history state.
* @return Whether or not the branch is taken.
*/
- bool lookup(Addr &branch_addr);
+ bool lookup(Addr &branch_addr, void * &bp_history);
/**
* Updates the branch predictor with the actual result of a branch.
* @param branch_addr The address of the branch to update.
* @param taken Whether or not the branch was taken.
*/
- void update(Addr &branch_addr, bool taken);
+ void update(Addr &branch_addr, bool taken, void *bp_history);
+
+ void squash(void *bp_history)
+ { assert(bp_history == NULL); }
void reset();
private:
-
/**
* Returns the taken/not taken prediction given the value of the
* counter.
Param<Tick> trapLatency;
Param<Tick> fetchTrapLatency;
+Param<std::string> predType;
Param<unsigned> localPredictorSize;
Param<unsigned> localCtrBits;
Param<unsigned> localHistoryTableSize;
INIT_PARAM_DFLT(trapLatency, "Number of cycles before the trap is handled", 6),
INIT_PARAM_DFLT(fetchTrapLatency, "Number of cycles before the fetch trap is handled", 12),
+ INIT_PARAM(predType, "Type of branch predictor ('local', 'tournament')"),
INIT_PARAM(localPredictorSize, "Size of local predictor"),
INIT_PARAM(localCtrBits, "Bits per counter"),
INIT_PARAM(localHistoryTableSize, "Size of local history table"),
params->trapLatency = trapLatency;
params->fetchTrapLatency = fetchTrapLatency;
+ params->predType = predType;
params->localPredictorSize = localPredictorSize;
params->localCtrBits = localCtrBits;
params->localHistoryTableSize = localHistoryTableSize;
//
// Branch predictor (BP & BTB)
//
+ std::string predType;
unsigned localPredictorSize;
unsigned localCtrBits;
unsigned localHistoryTableSize;
#include "cpu/ozone/ozone_impl.hh"
#include "cpu/ozone/simple_impl.hh"
-template class
TwobitBPredUnit<AlphaSimpleImpl>;
-template class TwobitBPredUnit<OzoneImpl>;
-template class TwobitBPredUnit<SimpleImpl>;
+template class BPredUnit<AlphaSimpleImpl>;
+template class BPredUnit<OzoneImpl>;
+template class BPredUnit<SimpleImpl>;
* and the BTB.
*/
template<class Impl>
-class TwobitBPredUnit
+class BPredUnit
{
- public:
+ private:
typedef typename Impl::Params Params;
typedef typename Impl::DynInstPtr DynInstPtr;
+ enum PredType {
+ Local,
+ Tournament
+ };
+
+ PredType predictor;
+
+ public:
+
/**
* @param params The params object, that has the size of the BP and BTB.
*/
- TwobitBPredUnit(Params *params);
+ BPredUnit(Params *params);
/**
* Registers statistics.
*/
bool predict(DynInstPtr &inst, Addr &PC, unsigned tid);
+ // @todo: Rename this function.
+ void BPUncond(void * &bp_history);
+
/**
* Tells the branch predictor to commit any updates until the given
* sequence number.
void squash(const InstSeqNum &squashed_sn, const Addr &corr_target,
bool actually_taken, unsigned tid);
+ /**
+ * @param bp_history Pointer to the history object. The predictor
+ * will need to update any state and delete the object.
+ */
+ void BPSquash(void *bp_history);
+
/**
* Looks up a given PC in the BP to see if it is taken or not taken.
* @param inst_PC The PC to look up.
+ * @param bp_history Pointer that will be set to an object that
+ * has the branch predictor state associated with the lookup.
* @return Whether the branch is taken or not taken.
*/
- bool BPLookup(Addr &inst_PC)
- { return BP.lookup(inst_PC); }
+ bool BPLookup(Addr &inst_PC, void * &bp_history);
/**
* Looks up a given PC in the BTB to see if a matching entry exists.
* Updates the BP with taken/not taken information.
* @param inst_PC The branch's PC that will be updated.
* @param taken Whether the branch was taken or not taken.
+ * @param bp_history Pointer to the branch predictor state that is
+ * associated with the branch lookup that is being updated.
* @todo Make this update flexible enough to handle a global predictor.
*/
- void BPUpdate(Addr &inst_PC, bool taken)
- { BP.update(inst_PC, taken); }
+ void BPUpdate(Addr &inst_PC, bool taken, void *bp_history);
/**
* Updates the BTB with the target of a branch.
void BTBUpdate(Addr &inst_PC, Addr &target_PC)
{ BTB.update(inst_PC, target_PC,0); }
+ void dump();
+
private:
struct PredictorHistory {
/**
- * Makes a predictor history struct that contains a sequence number,
- * the PC of its instruction, and whether or not it was predicted
- * taken.
+ * Makes a predictor history struct that contains any
+ * information needed to update the predictor, BTB, and RAS.
*/
PredictorHistory(const InstSeqNum &seq_num, const Addr &inst_PC,
- const bool pred_taken, const unsigned _tid)
- : seqNum(seq_num), PC(inst_PC), RASTarget(0), globalHistory(0),
+ const bool pred_taken, void *bp_history,
+ const unsigned _tid)
+ : seqNum(seq_num), PC(inst_PC), RASTarget(0),
RASIndex(0), tid(_tid), predTaken(pred_taken), usedRAS(0),
- wasCall(0)
+ wasCall(0), bpHistory(bp_history)
{ }
/** The sequence number for the predictor history entry. */
/** The RAS target (only valid if a return). */
Addr RASTarget;
- /** The global history at the time this entry was created. */
- unsigned globalHistory;
-
/** The RAS index of the instruction (only valid if a call). */
unsigned RASIndex;
/** Whether or not the instruction was a call. */
bool wasCall;
+
+ /** Pointer to the history object passed back from the branch
+ * predictor. It is used to update or restore state of the
+ * branch predictor.
+ */
+ void *bpHistory;
};
typedef std::list<PredictorHistory> History;
*/
History predHist[Impl::MaxThreads];
- /** The branch predictor. */
- DefaultBP BP;
+ /** The local branch predictor. */
+ LocalBP *localBP;
+
+ /** The tournament branch predictor. */
+ TournamentBP *tournamentBP;
/** The BTB. */
DefaultBTB BTB;
using namespace std;
template<class Impl>
-TwobitBPredUnit<Impl>::TwobitBPredUnit(Params *params)
- : BP(params->localPredictorSize,
- params->localCtrBits,
- params->instShiftAmt),
- BTB(params->BTBEntries,
+BPredUnit<Impl>::BPredUnit(Params *params)
+ : BTB(params->BTBEntries,
params->BTBTagSize,
params->instShiftAmt)
{
+ // Setup the selected predictor.
+ if (params->predType == "local") {
+ localBP = new LocalBP(params->localPredictorSize,
+ params->localCtrBits,
+ params->instShiftAmt);
+ predictor = Local;
+ } else if (params->predType == "tournament") {
+ tournamentBP = new TournamentBP(params->localPredictorSize,
+ params->localCtrBits,
+ params->localHistoryTableSize,
+ params->localHistoryBits,
+ params->globalPredictorSize,
+ params->globalHistoryBits,
+ params->globalCtrBits,
+ params->choicePredictorSize,
+ params->choiceCtrBits,
+ params->instShiftAmt);
+ predictor = Tournament;
+ } else {
+ fatal("Invalid BP selected!");
+ }
+
for (int i=0; i < Impl::MaxThreads; i++)
RAS[i].init(params->RASSize);
}
template <class Impl>
void
-TwobitBPredUnit<Impl>::regStats()
+BPredUnit<Impl>::regStats()
{
lookups
.name(name() + ".BPredUnit.lookups")
template <class Impl>
void
-TwobitBPredUnit<Impl>::switchOut()
+BPredUnit<Impl>::switchOut()
{
+ // Clear any state upon switch out.
for (int i = 0; i < Impl::MaxThreads; ++i) {
- predHist[i].clear();
+ squash(0, i);
}
}
template <class Impl>
void
-TwobitBPredUnit<Impl>::takeOverFrom()
+BPredUnit<Impl>::takeOverFrom()
{
+ // Can reset all predictor state, but it's not necessarily better
+ // than leaving it be.
/*
for (int i = 0; i < Impl::MaxThreads; ++i)
RAS[i].reset();
template <class Impl>
bool
-TwobitBPredUnit<Impl>::predict(DynInstPtr &inst, Addr &PC, unsigned tid)
+BPredUnit<Impl>::predict(DynInstPtr &inst, Addr &PC, unsigned tid)
{
// See if branch predictor predicts taken.
// If so, get its target addr either from the BTB or the RAS.
- // Once that's done, speculatively update the predictor?
// Save off record of branch stuff so the RAS can be fixed
// up once it's done.
++lookups;
+ void *bp_history = NULL;
+
if (inst->isUncondCtrl()) {
DPRINTF(Fetch, "BranchPred: [tid:%i] Unconditional control.\n", tid);
pred_taken = true;
+ // Tell the BP there was an unconditional branch.
+ BPUncond(bp_history);
} else {
++condPredicted;
- pred_taken = BPLookup(PC);
+ pred_taken = BPLookup(PC, bp_history);
DPRINTF(Fetch, "BranchPred: [tid:%i]: Branch predictor predicted %i "
"for PC %#x\n",
tid, pred_taken, inst->readPC());
}
- PredictorHistory predict_record(inst->seqNum, PC, pred_taken, tid);
+ PredictorHistory predict_record(inst->seqNum, PC, pred_taken,
+ bp_history, tid);
// Now lookup in the BTB or RAS.
if (pred_taken) {
if (BTB.valid(PC, tid)) {
++BTBHits;
- //If it's anything else, use the BTB to get the target addr.
+ // If it's not a return, use the BTB to get the target addr.
target = BTB.lookup(PC, tid);
DPRINTF(Fetch, "BranchPred: [tid:%i]: Instruction %#x predicted"
template <class Impl>
void
-TwobitBPredUnit<Impl>::update(const InstSeqNum &done_sn, unsigned tid)
+BPredUnit<Impl>::update(const InstSeqNum &done_sn, unsigned tid)
{
DPRINTF(Fetch, "BranchPred: [tid:%i]: Commiting branches until sequence"
"number %lli.\n", tid, done_sn);
while (!predHist[tid].empty() &&
predHist[tid].back().seqNum <= done_sn) {
// Update the branch predictor with the correct results.
- BP.update(predHist[tid].back().PC,
- predHist[tid].back().predTaken);
+ BPUpdate(predHist[tid].back().PC,
+ predHist[tid].back().predTaken,
+ predHist[tid].back().bpHistory);
predHist[tid].pop_back();
}
template <class Impl>
void
-TwobitBPredUnit<Impl>::squash(const InstSeqNum &squashed_sn, unsigned tid)
+BPredUnit<Impl>::squash(const InstSeqNum &squashed_sn, unsigned tid)
{
History &pred_hist = predHist[tid];
while (!pred_hist.empty() &&
pred_hist.front().seqNum > squashed_sn) {
- if (pred_hist.front().usedRAS) {
+ if (pred_hist.front().usedRAS) {
DPRINTF(Fetch, "BranchPred: [tid:%i]: Restoring top of RAS to: %i,"
" target: %#x.\n",
tid,
pred_hist.front().RASTarget);
} else if (pred_hist.front().wasCall) {
- DPRINTF(Fetch, "BranchPred: [tid:%i]: Removing speculative entry added "
- "to the RAS.\n",tid);
+ DPRINTF(Fetch, "BranchPred: [tid:%i]: Removing speculative entry "
+ "added to the RAS.\n",tid);
RAS[tid].pop();
}
+ // This call should delete the bpHistory.
+ BPSquash(pred_hist.front().bpHistory);
+
pred_hist.pop_front();
}
template <class Impl>
void
-TwobitBPredUnit<Impl>::squash(const InstSeqNum &squashed_sn,
- const Addr &corr_target,
- const bool actually_taken,
- unsigned tid)
+BPredUnit<Impl>::squash(const InstSeqNum &squashed_sn,
+ const Addr &corr_target,
+ const bool actually_taken,
+ unsigned tid)
{
// Now that we know that a branch was mispredicted, we need to undo
// all the branches that have been seen up until this branch and
"setting target to %#x.\n",
tid, squashed_sn, corr_target);
- while (!pred_hist.empty() &&
- pred_hist.front().seqNum > squashed_sn) {
- if (pred_hist.front().usedRAS) {
- DPRINTF(Fetch, "BranchPred: [tid:%i]: Restoring top of RAS to: %i, "
- "target: %#x.\n",
- tid,
- pred_hist.front().RASIndex,
- pred_hist.front().RASTarget);
-
- RAS[tid].restore(pred_hist.front().RASIndex,
- pred_hist.front().RASTarget);
- } else if (pred_hist.front().wasCall) {
- DPRINTF(Fetch, "BranchPred: [tid:%i]: Removing speculative entry"
- " added to the RAS.\n", tid);
-
- RAS[tid].pop();
- }
-
- pred_hist.pop_front();
- }
+ squash(squashed_sn, tid);
// If there's a squash due to a syscall, there may not be an entry
// corresponding to the squash. In that case, don't bother trying to
// fix up the entry.
if (!pred_hist.empty()) {
- pred_hist.front().predTaken = actually_taken;
-
+ assert(pred_hist.front().seqNum == squashed_sn);
if (pred_hist.front().usedRAS) {
++RASIncorrect;
}
- BP.update(pred_hist.front().PC, actually_taken);
+ BPUpdate(pred_hist.front().PC, actually_taken,
+ pred_hist.front().bpHistory);
BTB.update(pred_hist.front().PC, corr_target, tid);
pred_hist.pop_front();
}
}
+
+template <class Impl>
+void
+BPredUnit<Impl>::BPUncond(void * &bp_history)
+{
+ // Only the tournament predictor cares about unconditional branches.
+ if (predictor == Tournament) {
+ tournamentBP->uncondBr(bp_history);
+ }
+}
+
+template <class Impl>
+void
+BPredUnit<Impl>::BPSquash(void *bp_history)
+{
+ if (predictor == Local) {
+ localBP->squash(bp_history);
+ } else if (predictor == Tournament) {
+ tournamentBP->squash(bp_history);
+ } else {
+ panic("Predictor type is unexpected value!");
+ }
+}
+
+template <class Impl>
+bool
+BPredUnit<Impl>::BPLookup(Addr &inst_PC, void * &bp_history)
+{
+ if (predictor == Local) {
+ return localBP->lookup(inst_PC, bp_history);
+ } else if (predictor == Tournament) {
+ return tournamentBP->lookup(inst_PC, bp_history);
+ } else {
+ panic("Predictor type is unexpected value!");
+ }
+}
+
+template <class Impl>
+void
+BPredUnit<Impl>::BPUpdate(Addr &inst_PC, bool taken, void *bp_history)
+{
+ if (predictor == Local) {
+ localBP->update(inst_PC, taken, bp_history);
+ } else if (predictor == Tournament) {
+ tournamentBP->update(inst_PC, taken, bp_history);
+ } else {
+ panic("Predictor type is unexpected value!");
+ }
+}
+
+template <class Impl>
+void
+BPredUnit<Impl>::dump()
+{
+ typename History::iterator pred_hist_it;
+
+ for (int i = 0; i < Impl::MaxThreads; ++i) {
+ if (!predHist[i].empty()) {
+ pred_hist_it = predHist[i].begin();
+
+ cprintf("predHist[%i].size(): %i\n", i, predHist[i].size());
+
+ while (pred_hist_it != predHist[i].end()) {
+ cprintf("[sn:%lli], PC:%#x, tid:%i, predTaken:%i, "
+ "bpHistory:%#x\n",
+ (*pred_hist_it).seqNum, (*pred_hist_it).PC,
+ (*pred_hist_it).tid, (*pred_hist_it).predTaken,
+ (*pred_hist_it).bpHistory);
+ pred_hist_it++;
+ }
+
+ cprintf("\n");
+ }
+ }
+}
template<class Impl>
struct SimpleCPUPolicy
{
- typedef TwobitBPredUnit<Impl> BPredUnit;
+ typedef BPredUnit<Impl> BPredUnit;
typedef PhysRegFile<Impl> RegFile;
typedef SimpleFreeList FreeList;
typedef SimpleRenameMap RenameMap;
// Might want to set some sort of boolean and just do
// a check at the end
squash(inst, inst->threadNumber);
+ inst->setPredTarg(inst->branchTarget());
break;
}
/*
- * Copyright (c) 2004-2005 The Regents of The University of Michigan
+ * 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
* OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/
+#include "base/intmath.hh"
#include "cpu/o3/tournament_pred.hh"
TournamentBP::TournamentBP(unsigned _localPredictorSize,
choiceCtrBits(_choiceCtrBits),
instShiftAmt(_instShiftAmt)
{
- //Should do checks here to make sure sizes are correct (powers of 2)
+ if (!isPowerOf2(localPredictorSize)) {
+ fatal("Invalid local predictor size!\n");
+ }
//Setup the array of counters for the local predictor
localCtrs.resize(localPredictorSize);
for (int i = 0; i < localPredictorSize; ++i)
localCtrs[i].setBits(localCtrBits);
+ if (!isPowerOf2(localHistoryTableSize)) {
+ fatal("Invalid local history table size!\n");
+ }
+
//Setup the history table for the local table
localHistoryTable.resize(localHistoryTableSize);
// Setup the local history mask
localHistoryMask = (1 << localHistoryBits) - 1;
+ if (!isPowerOf2(globalPredictorSize)) {
+ fatal("Invalid global predictor size!\n");
+ }
+
//Setup the array of counters for the global predictor
globalCtrs.resize(globalPredictorSize);
// Setup the global history mask
globalHistoryMask = (1 << globalHistoryBits) - 1;
+ if (!isPowerOf2(choicePredictorSize)) {
+ fatal("Invalid choice predictor size!\n");
+ }
+
//Setup the array of counters for the choice predictor
choiceCtrs.resize(choicePredictorSize);
for (int i = 0; i < choicePredictorSize; ++i)
choiceCtrs[i].setBits(choiceCtrBits);
+ // @todo: Allow for different thresholds between the predictors.
threshold = (1 << (localCtrBits - 1)) - 1;
threshold = threshold / 2;
}
unsigned
TournamentBP::calcLocHistIdx(Addr &branch_addr)
{
+ // Get low order bits after removing instruction offset.
return (branch_addr >> instShiftAmt) & (localHistoryTableSize - 1);
}
inline
void
-TournamentBP::updateHistoriesTaken(unsigned local_history_idx)
+TournamentBP::updateGlobalHistTaken()
{
globalHistory = (globalHistory << 1) | 1;
globalHistory = globalHistory & globalHistoryMask;
-
- localHistoryTable[local_history_idx] =
- (localHistoryTable[local_history_idx] << 1) | 1;
}
inline
void
-TournamentBP::updateHistoriesNotTaken(unsigned local_history_idx)
+TournamentBP::updateGlobalHistNotTaken()
{
globalHistory = (globalHistory << 1);
globalHistory = globalHistory & globalHistoryMask;
+}
+inline
+void
+TournamentBP::updateLocalHistTaken(unsigned local_history_idx)
+{
+ localHistoryTable[local_history_idx] =
+ (localHistoryTable[local_history_idx] << 1) | 1;
+}
+
+inline
+void
+TournamentBP::updateLocalHistNotTaken(unsigned local_history_idx)
+{
localHistoryTable[local_history_idx] =
(localHistoryTable[local_history_idx] << 1);
}
bool
-TournamentBP::lookup(Addr &branch_addr)
+TournamentBP::lookup(Addr &branch_addr, void * &bp_history)
{
- uint8_t local_prediction;
+ bool local_prediction;
unsigned local_history_idx;
unsigned local_predictor_idx;
- uint8_t global_prediction;
- uint8_t choice_prediction;
+ bool global_prediction;
+ bool choice_prediction;
//Lookup in the local predictor to get its branch prediction
local_history_idx = calcLocHistIdx(branch_addr);
local_predictor_idx = localHistoryTable[local_history_idx]
& localHistoryMask;
- local_prediction = localCtrs[local_predictor_idx].read();
+ local_prediction = localCtrs[local_predictor_idx].read() > threshold;
//Lookup in the global predictor to get its branch prediction
- global_prediction = globalCtrs[globalHistory].read();
+ global_prediction = globalCtrs[globalHistory].read() > threshold;
//Lookup in the choice predictor to see which one to use
- choice_prediction = choiceCtrs[globalHistory].read();
-
- //@todo Put a threshold value in for the three predictors that can
- // be set through the constructor (so this isn't hard coded).
- //Also should put some of this code into functions.
- if (choice_prediction > threshold) {
- if (global_prediction > threshold) {
- updateHistoriesTaken(local_history_idx);
-
- assert(globalHistory < globalPredictorSize &&
- local_history_idx < localPredictorSize);
-
- globalCtrs[globalHistory].increment();
- localCtrs[local_history_idx].increment();
-
+ choice_prediction = choiceCtrs[globalHistory].read() > threshold;
+
+ // Create BPHistory and pass it back to be recorded.
+ BPHistory *history = new BPHistory;
+ history->globalHistory = globalHistory;
+ history->localPredTaken = local_prediction;
+ history->globalPredTaken = global_prediction;
+ history->globalUsed = choice_prediction;
+ bp_history = (void *)history;
+
+ assert(globalHistory < globalPredictorSize &&
+ local_history_idx < localPredictorSize);
+
+ // Commented code is for doing speculative update of counters and
+ // all histories.
+ if (choice_prediction) {
+ if (global_prediction) {
+// updateHistoriesTaken(local_history_idx);
+// globalCtrs[globalHistory].increment();
+// localCtrs[local_history_idx].increment();
+ updateGlobalHistTaken();
return true;
} else {
- updateHistoriesNotTaken(local_history_idx);
-
- assert(globalHistory < globalPredictorSize &&
- local_history_idx < localPredictorSize);
-
- globalCtrs[globalHistory].decrement();
- localCtrs[local_history_idx].decrement();
-
+// updateHistoriesNotTaken(local_history_idx);
+// globalCtrs[globalHistory].decrement();
+// localCtrs[local_history_idx].decrement();
+ updateGlobalHistNotTaken();
return false;
}
} else {
- if (local_prediction > threshold) {
- updateHistoriesTaken(local_history_idx);
-
- assert(globalHistory < globalPredictorSize &&
- local_history_idx < localPredictorSize);
-
- globalCtrs[globalHistory].increment();
- localCtrs[local_history_idx].increment();
-
+ if (local_prediction) {
+// updateHistoriesTaken(local_history_idx);
+// globalCtrs[globalHistory].increment();
+// localCtrs[local_history_idx].increment();
+ updateGlobalHistTaken();
return true;
} else {
- updateHistoriesNotTaken(local_history_idx);
-
- assert(globalHistory < globalPredictorSize &&
- local_history_idx < localPredictorSize);
-
- globalCtrs[globalHistory].decrement();
- localCtrs[local_history_idx].decrement();
-
+// updateHistoriesNotTaken(local_history_idx);
+// globalCtrs[globalHistory].decrement();
+// localCtrs[local_history_idx].decrement();
+ updateGlobalHistNotTaken();
return false;
}
}
}
-// Update the branch predictor if it predicted a branch wrong.
void
-TournamentBP::update(Addr &branch_addr, unsigned correct_gh, bool taken)
+TournamentBP::uncondBr(void * &bp_history)
{
+ // Create BPHistory and pass it back to be recorded.
+ BPHistory *history = new BPHistory;
+ history->globalHistory = globalHistory;
+ history->localPredTaken = true;
+ history->globalPredTaken = true;
+ bp_history = static_cast<void *>(history);
+
+ updateGlobalHistTaken();
+}
- uint8_t local_prediction;
+void
+TournamentBP::update(Addr &branch_addr, bool taken, void *bp_history)
+{
unsigned local_history_idx;
unsigned local_predictor_idx;
- bool local_pred_taken;
+ unsigned local_predictor_hist;
- uint8_t global_prediction;
- bool global_pred_taken;
-
- // Load the correct global history into the register.
- globalHistory = correct_gh;
-
- // Get the local predictor's current prediction, remove the incorrect
- // update, and update the local predictor
+ // Get the local predictor's current prediction
local_history_idx = calcLocHistIdx(branch_addr);
- local_predictor_idx = localHistoryTable[local_history_idx];
- local_predictor_idx = (local_predictor_idx >> 1) & localHistoryMask;
-
- local_prediction = localCtrs[local_predictor_idx].read();
- local_pred_taken = local_prediction > threshold;
-
- //Get the global predictor's current prediction, and update the
- //global predictor
- global_prediction = globalCtrs[globalHistory].read();
- global_pred_taken = global_prediction > threshold;
-
- //Update the choice predictor to tell it which one was correct
- if (local_pred_taken != global_pred_taken) {
- //If the local prediction matches the actual outcome, decerement
- //the counter. Otherwise increment the counter.
- if (local_pred_taken == taken) {
- choiceCtrs[globalHistory].decrement();
- } else {
- choiceCtrs[globalHistory].increment();
+ local_predictor_hist = localHistoryTable[local_history_idx];
+ local_predictor_idx = local_predictor_hist & localHistoryMask;
+
+ // Update the choice predictor to tell it which one was correct if
+ // there was a prediction.
+ if (bp_history) {
+ BPHistory *history = static_cast<BPHistory *>(bp_history);
+ if (history->localPredTaken != history->globalPredTaken) {
+ // If the local prediction matches the actual outcome,
+ // decerement the counter. Otherwise increment the
+ // counter.
+ if (history->localPredTaken == taken) {
+ choiceCtrs[globalHistory].decrement();
+ } else if (history->globalPredTaken == taken){
+ choiceCtrs[globalHistory].increment();
+ }
}
+
+ // We're done with this history, now delete it.
+ delete history;
}
- if (taken) {
- assert(globalHistory < globalPredictorSize &&
- local_predictor_idx < localPredictorSize);
+ assert(globalHistory < globalPredictorSize &&
+ local_predictor_idx < localPredictorSize);
+ // Update the counters and local history with the proper
+ // resolution of the branch. Global history is updated
+ // speculatively and restored upon squash() calls, so it does not
+ // need to be updated.
+ if (taken) {
localCtrs[local_predictor_idx].increment();
globalCtrs[globalHistory].increment();
- globalHistory = (globalHistory << 1) | 1;
- globalHistory = globalHistory & globalHistoryMask;
-
- localHistoryTable[local_history_idx] |= 1;
+ updateLocalHistTaken(local_history_idx);
} else {
- assert(globalHistory < globalPredictorSize &&
- local_predictor_idx < localPredictorSize);
-
localCtrs[local_predictor_idx].decrement();
globalCtrs[globalHistory].decrement();
- globalHistory = (globalHistory << 1);
- globalHistory = globalHistory & globalHistoryMask;
-
- localHistoryTable[local_history_idx] &= ~1;
+ updateLocalHistNotTaken(local_history_idx);
}
}
+
+void
+TournamentBP::squash(void *bp_history)
+{
+ BPHistory *history = static_cast<BPHistory *>(bp_history);
+
+ // Restore global history to state prior to this branch.
+ globalHistory = history->globalHistory;
+
+ // Delete this BPHistory now that we're done with it.
+ delete history;
+}
+
+#ifdef DEBUG
+int
+TournamentBP::BPHistory::newCount = 0;
+#endif
/*
- * Copyright (c) 2004-2005 The Regents of The University of Michigan
+ * 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
#include "cpu/o3/sat_counter.hh"
#include <vector>
+/**
+ * Implements a tournament branch predictor, hopefully identical to the one
+ * used in the 21264. It has a local predictor, which uses a local history
+ * table to index into a table of counters, and a global predictor, which
+ * uses a global history to index into a table of counters. A choice
+ * predictor chooses between the two. Only the global history register
+ * is speculatively updated, the rest are updated upon branches committing
+ * or misspeculating.
+ */
class TournamentBP
{
public:
/**
* Looks up the given address in the branch predictor and returns
- * a true/false value as to whether it is taken.
+ * a true/false value as to whether it is taken. Also creates a
+ * BPHistory object to store any state it will need on squash/update.
* @param branch_addr The address of the branch to look up.
+ * @param bp_history Pointer that will be set to the BPHistory object.
* @return Whether or not the branch is taken.
*/
- bool lookup(Addr &branch_addr);
+ bool lookup(Addr &branch_addr, void * &bp_history);
+
+ /**
+ * Records that there was an unconditional branch, and modifies
+ * the bp history to point to an object that has the previous
+ * global history stored in it.
+ * @param bp_history Pointer that will be set to the BPHistory object.
+ */
+ void uncondBr(void * &bp_history);
/**
* Updates the branch predictor with the actual result of a branch.
* @param branch_addr The address of the branch to update.
* @param taken Whether or not the branch was taken.
+ * @param bp_history Pointer to the BPHistory object that was created
+ * when the branch was predicted.
+ */
+ void update(Addr &branch_addr, bool taken, void *bp_history);
+
+ /**
+ * Restores the global branch history on a squash.
+ * @param bp_history Pointer to the BPHistory object that has the
+ * previous global branch history in it.
*/
- void update(Addr &branch_addr, unsigned global_history, bool taken);
+ void squash(void *bp_history);
+ /** Returns the global history. */
inline unsigned readGlobalHist() { return globalHistory; }
private:
-
+ /**
+ * Returns if the branch should be taken or not, given a counter
+ * value.
+ * @param count The counter value.
+ */
inline bool getPrediction(uint8_t &count);
+ /**
+ * Returns the local history index, given a branch address.
+ * @param branch_addr The branch's PC address.
+ */
inline unsigned calcLocHistIdx(Addr &branch_addr);
- inline void updateHistoriesTaken(unsigned local_history_idx);
+ /** Updates global history as taken. */
+ inline void updateGlobalHistTaken();
- inline void updateHistoriesNotTaken(unsigned local_history_idx);
+ /** Updates global history as not taken. */
+ inline void updateGlobalHistNotTaken();
+
+ /**
+ * Updates local histories as taken.
+ * @param local_history_idx The local history table entry that
+ * will be updated.
+ */
+ inline void updateLocalHistTaken(unsigned local_history_idx);
+
+ /**
+ * Updates local histories as not taken.
+ * @param local_history_idx The local history table entry that
+ * will be updated.
+ */
+ inline void updateLocalHistNotTaken(unsigned local_history_idx);
+
+ /**
+ * The branch history information that is created upon predicting
+ * a branch. It will be passed back upon updating and squashing,
+ * when the BP can use this information to update/restore its
+ * state properly.
+ */
+ struct BPHistory {
+#ifdef DEBUG
+ BPHistory()
+ { newCount++; }
+ ~BPHistory()
+ { newCount--; }
+
+ static int newCount;
+#endif
+ unsigned globalHistory;
+ bool localPredTaken;
+ bool globalPredTaken;
+ bool globalUsed;
+ };
/** Local counters. */
std::vector<SatCounter> localCtrs;
/** Mask to get the proper local history. */
unsigned localHistoryMask;
-
/** Array of counters that make up the global predictor. */
std::vector<SatCounter> globalCtrs;
/** Mask to get the proper global history. */
unsigned globalHistoryMask;
-
/** Array of counters that make up the choice predictor. */
std::vector<SatCounter> choiceCtrs;
// Would like to put these into their own area.
// typedef NullPredictor BranchPred;
- typedef TwobitBPredUnit<OzoneImpl> BranchPred;
+ typedef BPredUnit<OzoneImpl> BranchPred;
typedef FrontEnd<OzoneImpl> FrontEnd;
// Will need IQ, LSQ eventually
typedef LWBackEnd<OzoneImpl> BackEnd;
// Would like to put these into their own area.
// typedef NullPredictor BranchPred;
- typedef TwobitBPredUnit<SimpleImpl> BranchPred;
+ typedef BPredUnit<SimpleImpl> BranchPred;
typedef FrontEnd<SimpleImpl> FrontEnd;
// Will need IQ, LSQ eventually
typedef InorderBackEnd<SimpleImpl> BackEnd;
-
+/*
+ * Copyright (c) 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.
+ */
#ifndef __CPU_OZONE_SIMPLE_PARAMS_HH__
#define __CPU_OZONE_SIMPLE_PARAMS_HH__
AlphaITB *itb; AlphaDTB *dtb;
#else
std::vector<Process *> workload;
-// Process *process;
#endif // FULL_SYSTEM
//Page Table
//
// Branch predictor (BP & BTB)
//
+ std::string predType;
unsigned localPredictorSize;
unsigned localCtrBits;
unsigned localHistoryTableSize;
trapLatency = Param.Tick("Trap latency")
fetchTrapLatency = Param.Tick("Fetch trap latency")
+ predType = Param.String("Branch predictor type ('local', 'tournament')")
localPredictorSize = Param.Unsigned("Size of local predictor")
localCtrBits = Param.Unsigned("Bits per counter")
localHistoryTableSize = Param.Unsigned("Size of local history table")
commitWidth = Param.Unsigned("Commit width")
squashWidth = Param.Unsigned("Squash width")
+ predType = Param.String("Type of branch predictor ('local', 'tournament')")
localPredictorSize = Param.Unsigned("Size of local predictor")
localCtrBits = Param.Unsigned("Bits per counter")
localHistoryTableSize = Param.Unsigned("Size of local history table")
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