gem5  v21.2.1.1
Classes | Public Member Functions | Private Member Functions | Private Attributes | Static Private Attributes | List of all members
gem5::branch_prediction::TournamentBP Class Reference

Implements a tournament branch predictor, hopefully identical to the one used in the 21264. More...

#include <tournament.hh>

Inheritance diagram for gem5::branch_prediction::TournamentBP:
gem5::branch_prediction::BPredUnit gem5::SimObject gem5::EventManager gem5::Serializable gem5::Drainable gem5::statistics::Group gem5::Named

Classes

struct  BPHistory
 The branch history information that is created upon predicting a branch. More...
 

Public Member Functions

 TournamentBP (const TournamentBPParams &params)
 Default branch predictor constructor. More...
 
bool lookup (ThreadID tid, Addr branch_addr, void *&bp_history)
 Looks up the given address in the branch predictor and returns a true/false value as to whether it is taken. More...
 
void uncondBranch (ThreadID tid, Addr pc, 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. More...
 
void btbUpdate (ThreadID tid, Addr branch_addr, void *&bp_history)
 Updates the branch predictor to Not Taken if a BTB entry is invalid or not found. More...
 
void update (ThreadID tid, Addr branch_addr, bool taken, void *bp_history, bool squashed, const StaticInstPtr &inst, Addr corrTarget)
 Updates the branch predictor with the actual result of a branch. More...
 
void squash (ThreadID tid, void *bp_history)
 Restores the global branch history on a squash. More...
 
- Public Member Functions inherited from gem5::branch_prediction::BPredUnit
 BPredUnit (const Params &p)
 
void regProbePoints () override
 Register probe points for this object. More...
 
void drainSanityCheck () const
 Perform sanity checks after a drain. More...
 
bool predict (const StaticInstPtr &inst, const InstSeqNum &seqNum, PCStateBase &pc, ThreadID tid)
 Predicts whether or not the instruction is a taken branch, and the target of the branch if it is taken. More...
 
void update (const InstSeqNum &done_sn, ThreadID tid)
 Tells the branch predictor to commit any updates until the given sequence number. More...
 
void squash (const InstSeqNum &squashed_sn, ThreadID tid)
 Squashes all outstanding updates until a given sequence number. More...
 
void squash (const InstSeqNum &squashed_sn, const PCStateBase &corr_target, bool actually_taken, ThreadID tid)
 Squashes all outstanding updates until a given sequence number, and corrects that sn's update with the proper address and taken/not taken. More...
 
bool BTBValid (Addr instPC)
 Looks up a given PC in the BTB to see if a matching entry exists. More...
 
const PCStateBaseBTBLookup (Addr inst_pc)
 Looks up a given PC in the BTB to get the predicted target. More...
 
void BTBUpdate (Addr instPC, const PCStateBase &target)
 Updates the BTB with the target of a branch. More...
 
void dump ()
 
- Public Member Functions inherited from gem5::SimObject
const Paramsparams () const
 
 SimObject (const Params &p)
 
virtual ~SimObject ()
 
virtual void init ()
 init() is called after all C++ SimObjects have been created and all ports are connected. More...
 
virtual void loadState (CheckpointIn &cp)
 loadState() is called on each SimObject when restoring from a checkpoint. More...
 
virtual void initState ()
 initState() is called on each SimObject when not restoring from a checkpoint. More...
 
virtual void regProbeListeners ()
 Register probe listeners for this object. More...
 
ProbeManagergetProbeManager ()
 Get the probe manager for this object. More...
 
virtual PortgetPort (const std::string &if_name, PortID idx=InvalidPortID)
 Get a port with a given name and index. More...
 
virtual void startup ()
 startup() is the final initialization call before simulation. More...
 
DrainState drain () override
 Provide a default implementation of the drain interface for objects that don't need draining. More...
 
virtual void memWriteback ()
 Write back dirty buffers to memory using functional writes. More...
 
virtual void memInvalidate ()
 Invalidate the contents of memory buffers. More...
 
void serialize (CheckpointOut &cp) const override
 Serialize an object. More...
 
void unserialize (CheckpointIn &cp) override
 Unserialize an object. More...
 
- Public Member Functions inherited from gem5::EventManager
EventQueueeventQueue () const
 
void schedule (Event &event, Tick when)
 
void deschedule (Event &event)
 
void reschedule (Event &event, Tick when, bool always=false)
 
void schedule (Event *event, Tick when)
 
void deschedule (Event *event)
 
void reschedule (Event *event, Tick when, bool always=false)
 
void wakeupEventQueue (Tick when=(Tick) -1)
 This function is not needed by the usual gem5 event loop but may be necessary in derived EventQueues which host gem5 on other schedulers. More...
 
void setCurTick (Tick newVal)
 
 EventManager (EventManager &em)
 Event manger manages events in the event queue. More...
 
 EventManager (EventManager *em)
 
 EventManager (EventQueue *eq)
 
- Public Member Functions inherited from gem5::Serializable
 Serializable ()
 
virtual ~Serializable ()
 
void serializeSection (CheckpointOut &cp, const char *name) const
 Serialize an object into a new section. More...
 
void serializeSection (CheckpointOut &cp, const std::string &name) const
 
void unserializeSection (CheckpointIn &cp, const char *name)
 Unserialize an a child object. More...
 
void unserializeSection (CheckpointIn &cp, const std::string &name)
 
- Public Member Functions inherited from gem5::Drainable
DrainState drainState () const
 Return the current drain state of an object. More...
 
virtual void notifyFork ()
 Notify a child process of a fork. More...
 
- Public Member Functions inherited from gem5::statistics::Group
 Group (Group *parent, const char *name=nullptr)
 Construct a new statistics group. More...
 
virtual ~Group ()
 
virtual void regStats ()
 Callback to set stat parameters. More...
 
virtual void resetStats ()
 Callback to reset stats. More...
 
virtual void preDumpStats ()
 Callback before stats are dumped. More...
 
void addStat (statistics::Info *info)
 Register a stat with this group. More...
 
const std::map< std::string, Group * > & getStatGroups () const
 Get all child groups associated with this object. More...
 
const std::vector< Info * > & getStats () const
 Get all stats associated with this object. More...
 
void addStatGroup (const char *name, Group *block)
 Add a stat block as a child of this block. More...
 
const InforesolveStat (std::string name) const
 Resolve a stat by its name within this group. More...
 
void mergeStatGroup (Group *block)
 Merge the contents (stats & children) of a block to this block. More...
 
 Group ()=delete
 
 Group (const Group &)=delete
 
Groupoperator= (const Group &)=delete
 
- Public Member Functions inherited from gem5::Named
 Named (const std::string &name_)
 
virtual ~Named ()=default
 
virtual std::string name () const
 

Private Member Functions

bool getPrediction (uint8_t &count)
 Returns if the branch should be taken or not, given a counter value. More...
 
unsigned calcLocHistIdx (Addr &branch_addr)
 Returns the local history index, given a branch address. More...
 
void updateGlobalHistTaken (ThreadID tid)
 Updates global history as taken. More...
 
void updateGlobalHistNotTaken (ThreadID tid)
 Updates global history as not taken. More...
 
void updateLocalHistTaken (unsigned local_history_idx)
 Updates local histories as taken. More...
 
void updateLocalHistNotTaken (unsigned local_history_idx)
 Updates local histories as not taken. More...
 

Private Attributes

unsigned localPredictorSize
 Number of counters in the local predictor. More...
 
unsigned localPredictorMask
 Mask to truncate values stored in the local history table. More...
 
unsigned localCtrBits
 Number of bits of the local predictor's counters. More...
 
std::vector< SatCounter8localCtrs
 Local counters. More...
 
std::vector< unsigned > localHistoryTable
 Array of local history table entries. More...
 
unsigned localHistoryTableSize
 Number of entries in the local history table. More...
 
unsigned localHistoryBits
 Number of bits for each entry of the local history table. More...
 
unsigned globalPredictorSize
 Number of entries in the global predictor. More...
 
unsigned globalCtrBits
 Number of bits of the global predictor's counters. More...
 
std::vector< SatCounter8globalCtrs
 Array of counters that make up the global predictor. More...
 
std::vector< unsigned > globalHistory
 Global history register. More...
 
unsigned globalHistoryBits
 Number of bits for the global history. More...
 
unsigned globalHistoryMask
 Mask to apply to globalHistory to access global history table. More...
 
unsigned choiceHistoryMask
 Mask to apply to globalHistory to access choice history table. More...
 
unsigned historyRegisterMask
 Mask to control how much history is stored. More...
 
unsigned choicePredictorSize
 Number of entries in the choice predictor. More...
 
unsigned choiceCtrBits
 Number of bits in the choice predictor's counters. More...
 
std::vector< SatCounter8choiceCtrs
 Array of counters that make up the choice predictor. More...
 
unsigned localThreshold
 Thresholds for the counter value; above the threshold is taken, equal to or below the threshold is not taken. More...
 
unsigned globalThreshold
 
unsigned choiceThreshold
 

Static Private Attributes

static const int invalidPredictorIndex = -1
 Flag for invalid predictor index. More...
 

Additional Inherited Members

- Public Types inherited from gem5::branch_prediction::BPredUnit
typedef BranchPredictorParams Params
 
- Public Types inherited from gem5::SimObject
typedef SimObjectParams Params
 
- Static Public Member Functions inherited from gem5::SimObject
static void serializeAll (const std::string &cpt_dir)
 Create a checkpoint by serializing all SimObjects in the system. More...
 
static SimObjectfind (const char *name)
 Find the SimObject with the given name and return a pointer to it. More...
 
static void setSimObjectResolver (SimObjectResolver *resolver)
 There is a single object name resolver, and it is only set when simulation is restoring from checkpoints. More...
 
static SimObjectResolvergetSimObjectResolver ()
 There is a single object name resolver, and it is only set when simulation is restoring from checkpoints. More...
 
- Static Public Member Functions inherited from gem5::Serializable
static const std::string & currentSection ()
 Gets the fully-qualified name of the active section. More...
 
static void generateCheckpointOut (const std::string &cpt_dir, std::ofstream &outstream)
 Generate a checkpoint file so that the serialization can be routed to it. More...
 
- Protected Member Functions inherited from gem5::branch_prediction::BPredUnit
probing::PMUUPtr pmuProbePoint (const char *name)
 Helper method to instantiate probe points belonging to this object. More...
 
- Protected Member Functions inherited from gem5::Drainable
 Drainable ()
 
virtual ~Drainable ()
 
virtual void drainResume ()
 Resume execution after a successful drain. More...
 
void signalDrainDone () const
 Signal that an object is drained. More...
 
- Protected Attributes inherited from gem5::branch_prediction::BPredUnit
const unsigned instShiftAmt
 Number of bits to shift instructions by for predictor addresses. More...
 
probing::PMUUPtr ppBranches
 Branches seen by the branch predictor. More...
 
probing::PMUUPtr ppMisses
 Miss-predicted branches. More...
 
- Protected Attributes inherited from gem5::SimObject
const SimObjectParams & _params
 Cached copy of the object parameters. More...
 
- Protected Attributes inherited from gem5::EventManager
EventQueueeventq
 A pointer to this object's event queue. More...
 

Detailed Description

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. Both the global history register and the selected local history are speculatively updated.

Definition at line 65 of file tournament.hh.

Constructor & Destructor Documentation

◆ TournamentBP()

gem5::branch_prediction::TournamentBP::TournamentBP ( const TournamentBPParams &  params)

Member Function Documentation

◆ btbUpdate()

void gem5::branch_prediction::TournamentBP::btbUpdate ( ThreadID  tid,
Addr  branch_addr,
void *&  bp_history 
)
virtual

Updates the branch predictor to Not Taken if a BTB entry is invalid or not found.

Parameters
branch_addrThe address of the branch to look up.
bp_historyPointer to any bp history state.
Returns
Whether or not the branch is taken.

Implements gem5::branch_prediction::BPredUnit.

Definition at line 169 of file tournament.cc.

References calcLocHistIdx(), globalHistory, historyRegisterMask, localHistoryTable, and localPredictorMask.

◆ calcLocHistIdx()

unsigned gem5::branch_prediction::TournamentBP::calcLocHistIdx ( Addr branch_addr)
inlineprivate

Returns the local history index, given a branch address.

Parameters
branch_addrThe branch's PC address.

Definition at line 129 of file tournament.cc.

References gem5::branch_prediction::BPredUnit::instShiftAmt, and localHistoryTableSize.

Referenced by btbUpdate(), lookup(), and update().

◆ getPrediction()

bool gem5::branch_prediction::TournamentBP::getPrediction ( uint8_t &  count)
inlineprivate

Returns if the branch should be taken or not, given a counter value.

Parameters
countThe counter value.

◆ lookup()

bool gem5::branch_prediction::TournamentBP::lookup ( ThreadID  tid,
Addr  branch_addr,
void *&  bp_history 
)
virtual

◆ squash()

void gem5::branch_prediction::TournamentBP::squash ( ThreadID  tid,
void *  bp_history 
)
virtual

Restores the global branch history on a squash.

Parameters
bp_historyPointer to the BPHistory object that has the previous global branch history in it.

Implements gem5::branch_prediction::BPredUnit.

Definition at line 336 of file tournament.cc.

References gem5::branch_prediction::TournamentBP::BPHistory::globalHistory, globalHistory, invalidPredictorIndex, gem5::branch_prediction::TournamentBP::BPHistory::localHistory, gem5::branch_prediction::TournamentBP::BPHistory::localHistoryIdx, and localHistoryTable.

◆ uncondBranch()

void gem5::branch_prediction::TournamentBP::uncondBranch ( ThreadID  tid,
Addr  pc,
void *&  bp_history 
)
virtual

◆ update()

void gem5::branch_prediction::TournamentBP::update ( ThreadID  tid,
Addr  branch_addr,
bool  taken,
void *  bp_history,
bool  squashed,
const StaticInstPtr inst,
Addr  corrTarget 
)
virtual

Updates the branch predictor with the actual result of a branch.

Parameters
branch_addrThe address of the branch to update.
takenWhether or not the branch was taken.
bp_historyPointer to the BPHistory object that was created when the branch was predicted.
squashedis set when this function is called during a squash operation.
instStatic instruction information
corrTargetResolved target of the branch (only needed if squashed)

Implements gem5::branch_prediction::BPredUnit.

Definition at line 257 of file tournament.cc.

References calcLocHistIdx(), choiceCtrs, choiceHistoryMask, globalCtrs, gem5::branch_prediction::TournamentBP::BPHistory::globalHistory, globalHistory, globalHistoryMask, gem5::branch_prediction::TournamentBP::BPHistory::globalPredTaken, historyRegisterMask, invalidPredictorIndex, localCtrs, gem5::branch_prediction::TournamentBP::BPHistory::localHistory, localHistoryTable, localHistoryTableSize, localPredictorMask, localPredictorSize, and gem5::branch_prediction::TournamentBP::BPHistory::localPredTaken.

◆ updateGlobalHistNotTaken()

void gem5::branch_prediction::TournamentBP::updateGlobalHistNotTaken ( ThreadID  tid)
inlineprivate

Updates global history as not taken.

Definition at line 145 of file tournament.cc.

References globalHistory, and historyRegisterMask.

Referenced by lookup().

◆ updateGlobalHistTaken()

void gem5::branch_prediction::TournamentBP::updateGlobalHistTaken ( ThreadID  tid)
inlineprivate

Updates global history as taken.

Definition at line 137 of file tournament.cc.

References globalHistory, and historyRegisterMask.

Referenced by lookup(), and uncondBranch().

◆ updateLocalHistNotTaken()

void gem5::branch_prediction::TournamentBP::updateLocalHistNotTaken ( unsigned  local_history_idx)
inlineprivate

Updates local histories as not taken.

Parameters
local_history_idxThe local history table entry that will be updated.

Definition at line 161 of file tournament.cc.

References localHistoryTable.

Referenced by lookup().

◆ updateLocalHistTaken()

void gem5::branch_prediction::TournamentBP::updateLocalHistTaken ( unsigned  local_history_idx)
inlineprivate

Updates local histories as taken.

Parameters
local_history_idxThe local history table entry that will be updated.

Definition at line 153 of file tournament.cc.

References localHistoryTable.

Referenced by lookup().

Member Data Documentation

◆ choiceCtrBits

unsigned gem5::branch_prediction::TournamentBP::choiceCtrBits
private

Number of bits in the choice predictor's counters.

Definition at line 235 of file tournament.hh.

Referenced by TournamentBP().

◆ choiceCtrs

std::vector<SatCounter8> gem5::branch_prediction::TournamentBP::choiceCtrs
private

Array of counters that make up the choice predictor.

Definition at line 238 of file tournament.hh.

Referenced by lookup(), and update().

◆ choiceHistoryMask

unsigned gem5::branch_prediction::TournamentBP::choiceHistoryMask
private

Mask to apply to globalHistory to access choice history table.

Based on choicePredictorSize.

Definition at line 225 of file tournament.hh.

Referenced by lookup(), TournamentBP(), and update().

◆ choicePredictorSize

unsigned gem5::branch_prediction::TournamentBP::choicePredictorSize
private

Number of entries in the choice predictor.

Definition at line 232 of file tournament.hh.

Referenced by TournamentBP().

◆ choiceThreshold

unsigned gem5::branch_prediction::TournamentBP::choiceThreshold
private

Definition at line 245 of file tournament.hh.

Referenced by lookup(), and TournamentBP().

◆ globalCtrBits

unsigned gem5::branch_prediction::TournamentBP::globalCtrBits
private

Number of bits of the global predictor's counters.

Definition at line 205 of file tournament.hh.

Referenced by TournamentBP().

◆ globalCtrs

std::vector<SatCounter8> gem5::branch_prediction::TournamentBP::globalCtrs
private

Array of counters that make up the global predictor.

Definition at line 208 of file tournament.hh.

Referenced by lookup(), and update().

◆ globalHistory

std::vector<unsigned> gem5::branch_prediction::TournamentBP::globalHistory
private

Global history register.

Contains as much history as specified by globalHistoryBits. Actual number of bits used is determined by globalHistoryMask and choiceHistoryMask.

Definition at line 213 of file tournament.hh.

Referenced by btbUpdate(), lookup(), squash(), uncondBranch(), update(), updateGlobalHistNotTaken(), and updateGlobalHistTaken().

◆ globalHistoryBits

unsigned gem5::branch_prediction::TournamentBP::globalHistoryBits
private

Number of bits for the global history.

Determines maximum number of entries in global and choice predictor tables.

Definition at line 217 of file tournament.hh.

Referenced by TournamentBP().

◆ globalHistoryMask

unsigned gem5::branch_prediction::TournamentBP::globalHistoryMask
private

Mask to apply to globalHistory to access global history table.

Based on globalPredictorSize.

Definition at line 221 of file tournament.hh.

Referenced by lookup(), TournamentBP(), and update().

◆ globalPredictorSize

unsigned gem5::branch_prediction::TournamentBP::globalPredictorSize
private

Number of entries in the global predictor.

Definition at line 202 of file tournament.hh.

Referenced by TournamentBP().

◆ globalThreshold

unsigned gem5::branch_prediction::TournamentBP::globalThreshold
private

Definition at line 244 of file tournament.hh.

Referenced by lookup(), and TournamentBP().

◆ historyRegisterMask

unsigned gem5::branch_prediction::TournamentBP::historyRegisterMask
private

Mask to control how much history is stored.

All of it might not be used.

Definition at line 229 of file tournament.hh.

Referenced by btbUpdate(), TournamentBP(), update(), updateGlobalHistNotTaken(), and updateGlobalHistTaken().

◆ invalidPredictorIndex

const int gem5::branch_prediction::TournamentBP::invalidPredictorIndex = -1
staticprivate

Flag for invalid predictor index.

Definition at line 179 of file tournament.hh.

Referenced by squash(), uncondBranch(), and update().

◆ localCtrBits

unsigned gem5::branch_prediction::TournamentBP::localCtrBits
private

Number of bits of the local predictor's counters.

Definition at line 187 of file tournament.hh.

Referenced by TournamentBP().

◆ localCtrs

std::vector<SatCounter8> gem5::branch_prediction::TournamentBP::localCtrs
private

Local counters.

Definition at line 190 of file tournament.hh.

Referenced by lookup(), and update().

◆ localHistoryBits

unsigned gem5::branch_prediction::TournamentBP::localHistoryBits
private

Number of bits for each entry of the local history table.

Definition at line 199 of file tournament.hh.

Referenced by TournamentBP().

◆ localHistoryTable

std::vector<unsigned> gem5::branch_prediction::TournamentBP::localHistoryTable
private

Array of local history table entries.

Definition at line 193 of file tournament.hh.

Referenced by btbUpdate(), lookup(), squash(), TournamentBP(), update(), updateLocalHistNotTaken(), and updateLocalHistTaken().

◆ localHistoryTableSize

unsigned gem5::branch_prediction::TournamentBP::localHistoryTableSize
private

Number of entries in the local history table.

Definition at line 196 of file tournament.hh.

Referenced by calcLocHistIdx(), lookup(), TournamentBP(), and update().

◆ localPredictorMask

unsigned gem5::branch_prediction::TournamentBP::localPredictorMask
private

Mask to truncate values stored in the local history table.

Definition at line 184 of file tournament.hh.

Referenced by btbUpdate(), lookup(), TournamentBP(), and update().

◆ localPredictorSize

unsigned gem5::branch_prediction::TournamentBP::localPredictorSize
private

Number of counters in the local predictor.

Definition at line 181 of file tournament.hh.

Referenced by TournamentBP(), and update().

◆ localThreshold

unsigned gem5::branch_prediction::TournamentBP::localThreshold
private

Thresholds for the counter value; above the threshold is taken, equal to or below the threshold is not taken.

Definition at line 243 of file tournament.hh.

Referenced by lookup(), and TournamentBP().


The documentation for this class was generated from the following files:

Generated on Wed May 4 2022 12:15:02 for gem5 by doxygen 1.8.17