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

#include <tournament.hh>

Inheritance diagram for TournamentBP:

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 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, TheISA::PCState &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 TheISA::PCState &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...

TheISA::PCState	BTBLookup (Addr instPC)
	Looks up a given PC in the BTB to get the predicted target. More...

void	BTBUpdate (Addr instPC, const TheISA::PCState &target)
	Updates the BTB with the target of a branch. More...

void	dump ()

Public Member Functions inherited from SimObject
const Params *	params () const

	SimObject (const Params *_params)

virtual	~SimObject ()

virtual const std::string	name () const

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...

ProbeManager *	getProbeManager ()
	Get the probe manager for this object. More...

virtual Port &	getPort (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 EventManager
EventQueue *	eventQueue () 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 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 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 Stats::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 (Stats::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 Info *	resolveStat (std::string name) const
	Resolve a stat by its name within this group. More...

	Group ()=delete

	Group (const Group &)=delete

Group &	operator= (const Group &)=delete

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< SatCounter >	localCtrs
	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< SatCounter >	globalCtrs
	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< SatCounter >	choiceCtrs
	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 BPredUnit
typedef BranchPredictorParams	Params

Public Types inherited from SimObject
typedef SimObjectParams	Params

Static Public Member Functions inherited from SimObject
static void	serializeAll (CheckpointOut &cp)
	Serialize all SimObjects in the system. More...

static SimObject *	find (const char *name)
	Find the SimObject with the given name and return a pointer to it. More...

Static Public Member Functions inherited from Serializable
static const std::string &	currentSection ()
	Gets the fully-qualified name of the active section. More...

static void	serializeAll (const std::string &cpt_dir)
	Serializes all the SimObjects. More...

static void	unserializeGlobals (CheckpointIn &cp)

Protected Member Functions inherited from BPredUnit
ProbePoints::PMUUPtr	pmuProbePoint (const char *name)
	Helper method to instantiate probe points belonging to this object. More...

Protected Member Functions inherited from 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 BPredUnit
const unsigned	instShiftAmt
	Number of bits to shift instructions by for predictor addresses. More...

ProbePoints::PMUUPtr	ppBranches
	Branches seen by the branch predictor. More...

ProbePoints::PMUUPtr	ppMisses
	Miss-predicted branches. More...

Protected Attributes inherited from SimObject
const SimObjectParams *	_params
	Cached copy of the object parameters. More...

Protected Attributes inherited from EventManager
EventQueue *	eventq
	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 59 of file tournament.hh.

Constructor & Destructor Documentation

◆ TournamentBP()

TournamentBP::TournamentBP ( const TournamentBPParams * params )

Default branch predictor constructor.

Definition at line 46 of file tournament.cc.

References choiceCtrBits, choiceHistoryMask, choicePredictorSize, choiceThreshold, fatal, globalCtrBits, globalHistoryBits, globalHistoryMask, globalPredictorSize, globalThreshold, historyRegisterMask, ArmISA::i, inform, isPowerOf2(), localCtrBits, localHistoryBits, localHistoryTable, localHistoryTableSize, localPredictorMask, localPredictorSize, localThreshold, ArmISA::mask, and ULL.

Member Function Documentation

◆ btbUpdate()

void 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_addr	The address of the branch to look up.
bp_history	Pointer to any bp history state.

Returns: Whether or not the branch is taken.

Implements BPredUnit.

Definition at line 163 of file tournament.cc.

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

◆ calcLocHistIdx()

unsigned TournamentBP::calcLocHistIdx ( Addr & branch_addr )

inlineprivate

Returns the local history index, given a branch address.

Parameters

branch_addr The branch's PC address.

Definition at line 123 of file tournament.cc.

References BPredUnit::instShiftAmt, and localHistoryTableSize.

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

◆ getPrediction()

bool TournamentBP::getPrediction ( uint8_t & count )

inlineprivate

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

Parameters

count The counter value.

◆ lookup()

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

virtual

Looks up the given address in the branch predictor and returns 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.

Parameters

branch_addr	The address of the branch to look up.
bp_history	Pointer that will be set to the BPHistory object.

Returns: Whether or not the branch is taken.

Implements BPredUnit.

Definition at line 174 of file tournament.cc.

References calcLocHistIdx(), choiceCtrs, choiceHistoryMask, choiceThreshold, globalCtrs, TournamentBP::BPHistory::globalHistory, globalHistory, globalHistoryMask, TournamentBP::BPHistory::globalPredTaken, globalThreshold, TournamentBP::BPHistory::globalUsed, localCtrs, TournamentBP::BPHistory::localHistory, TournamentBP::BPHistory::localHistoryIdx, localHistoryTable, localHistoryTableSize, localPredictorMask, TournamentBP::BPHistory::localPredTaken, localThreshold, updateGlobalHistNotTaken(), updateGlobalHistTaken(), updateLocalHistNotTaken(), and updateLocalHistTaken().

◆ squash()

void TournamentBP::squash	(	ThreadID	tid,
		void *	bp_history
	)

virtual

Restores the global branch history on a squash.

Parameters

bp_history Pointer to the BPHistory object that has the previous global branch history in it.

Implements BPredUnit.

Definition at line 330 of file tournament.cc.

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

◆ uncondBranch()

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

virtual

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.

Parameters

bp_history Pointer that will be set to the BPHistory object.

Implements BPredUnit.

Definition at line 235 of file tournament.cc.

References TournamentBP::BPHistory::globalHistory, globalHistory, TournamentBP::BPHistory::globalPredTaken, TournamentBP::BPHistory::globalUsed, invalidPredictorIndex, TournamentBP::BPHistory::localHistory, TournamentBP::BPHistory::localHistoryIdx, TournamentBP::BPHistory::localPredTaken, and updateGlobalHistTaken().

◆ update()

void 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_addr	The address of the branch to update.
taken	Whether or not the branch was taken.
bp_history	Pointer to the BPHistory object that was created when the branch was predicted.
squashed	is set when this function is called during a squash operation.
inst	Static instruction information
corrTarget	Resolved target of the branch (only needed if squashed)

Implements BPredUnit.

Definition at line 251 of file tournament.cc.

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

◆ updateGlobalHistNotTaken()

void TournamentBP::updateGlobalHistNotTaken ( ThreadID tid )

inlineprivate

Updates global history as not taken.

Definition at line 139 of file tournament.cc.

References globalHistory, and historyRegisterMask.

Referenced by lookup().

◆ updateGlobalHistTaken()

void TournamentBP::updateGlobalHistTaken ( ThreadID tid )

inlineprivate

Updates global history as taken.

Definition at line 131 of file tournament.cc.

References globalHistory, and historyRegisterMask.

Referenced by lookup(), and uncondBranch().

◆ updateLocalHistNotTaken()

void TournamentBP::updateLocalHistNotTaken ( unsigned local_history_idx )

inlineprivate

Updates local histories as not taken.

Parameters

local_history_idx The local history table entry that will be updated.

Definition at line 155 of file tournament.cc.

References localHistoryTable.

Referenced by lookup().

◆ updateLocalHistTaken()

void TournamentBP::updateLocalHistTaken ( unsigned local_history_idx )

inlineprivate

Updates local histories as taken.

Parameters

local_history_idx The local history table entry that will be updated.

Definition at line 147 of file tournament.cc.

References localHistoryTable.

Referenced by lookup().

Member Data Documentation

◆ choiceCtrBits

unsigned TournamentBP::choiceCtrBits

private

Number of bits in the choice predictor's counters.

Definition at line 228 of file tournament.hh.

Referenced by TournamentBP().

◆ choiceCtrs

std::vector<SatCounter> TournamentBP::choiceCtrs

private

Array of counters that make up the choice predictor.

Definition at line 231 of file tournament.hh.

Referenced by lookup(), and update().

◆ choiceHistoryMask

unsigned TournamentBP::choiceHistoryMask

private

Mask to apply to globalHistory to access choice history table.

Based on choicePredictorSize.

Definition at line 218 of file tournament.hh.

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

◆ choicePredictorSize

unsigned TournamentBP::choicePredictorSize

private

Number of entries in the choice predictor.

Definition at line 225 of file tournament.hh.

Referenced by TournamentBP().

◆ choiceThreshold

unsigned TournamentBP::choiceThreshold

private

Definition at line 238 of file tournament.hh.

Referenced by lookup(), and TournamentBP().

◆ globalCtrBits

unsigned TournamentBP::globalCtrBits

private

Number of bits of the global predictor's counters.

Definition at line 198 of file tournament.hh.

Referenced by TournamentBP().

◆ globalCtrs

std::vector<SatCounter> TournamentBP::globalCtrs

private

Array of counters that make up the global predictor.

Definition at line 201 of file tournament.hh.

Referenced by lookup(), and update().

◆ globalHistory

std::vector<unsigned> 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 206 of file tournament.hh.

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

◆ globalHistoryBits

unsigned TournamentBP::globalHistoryBits

private

Number of bits for the global history.

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

Definition at line 210 of file tournament.hh.

Referenced by TournamentBP().

◆ globalHistoryMask

unsigned TournamentBP::globalHistoryMask

private

Mask to apply to globalHistory to access global history table.

Based on globalPredictorSize.

Definition at line 214 of file tournament.hh.

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

◆ globalPredictorSize

unsigned TournamentBP::globalPredictorSize

private

Number of entries in the global predictor.

Definition at line 195 of file tournament.hh.

Referenced by TournamentBP().

◆ globalThreshold

unsigned TournamentBP::globalThreshold

private

Definition at line 237 of file tournament.hh.

Referenced by lookup(), and TournamentBP().

◆ historyRegisterMask

unsigned TournamentBP::historyRegisterMask

private

Mask to control how much history is stored.

All of it might not be used.

Definition at line 222 of file tournament.hh.

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

◆ invalidPredictorIndex

const int TournamentBP::invalidPredictorIndex = -1

staticprivate

Flag for invalid predictor index.

Definition at line 172 of file tournament.hh.

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

◆ localCtrBits

unsigned TournamentBP::localCtrBits

private

Number of bits of the local predictor's counters.

Definition at line 180 of file tournament.hh.

Referenced by TournamentBP().

◆ localCtrs

std::vector<SatCounter> TournamentBP::localCtrs

private

Local counters.

Definition at line 183 of file tournament.hh.

Referenced by lookup(), and update().

◆ localHistoryBits

unsigned TournamentBP::localHistoryBits

private

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

Definition at line 192 of file tournament.hh.

Referenced by TournamentBP().

◆ localHistoryTable

std::vector<unsigned> TournamentBP::localHistoryTable

private

Array of local history table entries.

Definition at line 186 of file tournament.hh.

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

◆ localHistoryTableSize

unsigned TournamentBP::localHistoryTableSize

private

Number of entries in the local history table.

Definition at line 189 of file tournament.hh.

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

◆ localPredictorMask

unsigned TournamentBP::localPredictorMask

private

Mask to truncate values stored in the local history table.

Definition at line 177 of file tournament.hh.

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

◆ localPredictorSize

unsigned TournamentBP::localPredictorSize

private

Number of counters in the local predictor.

Definition at line 174 of file tournament.hh.

Referenced by TournamentBP(), and update().

◆ localThreshold

unsigned 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 236 of file tournament.hh.

Referenced by lookup(), and TournamentBP().

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

cpu/pred/tournament.hh
cpu/pred/tournament.cc

Classes

Public Member Functions

Private Member Functions

Private Attributes

Static Private Attributes

Additional Inherited Members

Detailed Description

Constructor & Destructor Documentation

◆ TournamentBP()

Member Function Documentation

◆ btbUpdate()

◆ calcLocHistIdx()

◆ getPrediction()

◆ lookup()

◆ squash()

◆ uncondBranch()

◆ update()

◆ updateGlobalHistNotTaken()

◆ updateGlobalHistTaken()

◆ updateLocalHistNotTaken()

◆ updateLocalHistTaken()

Member Data Documentation

◆ choiceCtrBits

◆ choiceCtrs

◆ choiceHistoryMask

◆ choicePredictorSize

◆ choiceThreshold

◆ globalCtrBits

◆ globalCtrs

◆ globalHistory

◆ globalHistoryBits

◆ globalHistoryMask

◆ globalPredictorSize

◆ globalThreshold

◆ historyRegisterMask

◆ invalidPredictorIndex

◆ localCtrBits

◆ localCtrs

◆ localHistoryBits

◆ localHistoryTable

◆ localHistoryTableSize

◆ localPredictorMask

◆ localPredictorSize

◆ localThreshold