gem5
v22.1.0.0
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Implements a tournament branch predictor, hopefully identical to the one used in the 21264. More...
#include <tournament.hh>
Classes | |
struct | BPHistory |
The branch history information that is created upon predicting a branch. More... | |
Public Member Functions | |
TournamentBP (const TournamentBPParams ¶ms) | |
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... | |
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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 PCStateBase * | BTBLookup (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 () |
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const Params & | params () 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... | |
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... | |
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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) | |
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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) |
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DrainState | drainState () const |
Return the current drain state of an object. More... | |
virtual void | notifyFork () |
Notify a child process of a fork. More... | |
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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 Info * | resolveStat (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 | |
Group & | operator= (const Group &)=delete |
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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< SatCounter8 > | 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< SatCounter8 > | 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< SatCounter8 > | 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 | |
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typedef BranchPredictorParams | Params |
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typedef SimObjectParams | Params |
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static void | serializeAll (const std::string &cpt_dir) |
Create a checkpoint by serializing 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 void | setSimObjectResolver (SimObjectResolver *resolver) |
There is a single object name resolver, and it is only set when simulation is restoring from checkpoints. More... | |
static SimObjectResolver * | getSimObjectResolver () |
There is a single object name resolver, and it is only set when simulation is restoring from checkpoints. More... | |
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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... | |
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probing::PMUUPtr | pmuProbePoint (const char *name) |
Helper method to instantiate probe points belonging to this object. More... | |
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Drainable () | |
virtual | ~Drainable () |
virtual void | drainResume () |
Resume execution after a successful drain. More... | |
void | signalDrainDone () const |
Signal that an object is drained. More... | |
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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... | |
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const SimObjectParams & | _params |
Cached copy of the object parameters. More... | |
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EventQueue * | eventq |
A pointer to this object's event queue. More... | |
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.
gem5::branch_prediction::TournamentBP::TournamentBP | ( | const TournamentBPParams & | params | ) |
Default branch predictor constructor.
Definition at line 52 of file tournament.cc.
References choiceCtrBits, choiceHistoryMask, choicePredictorSize, choiceThreshold, fatal, globalCtrBits, globalHistoryBits, globalHistoryMask, globalPredictorSize, globalThreshold, historyRegisterMask, gem5::ArmISA::i, inform, gem5::isPowerOf2(), localCtrBits, localHistoryBits, localHistoryTable, localHistoryTableSize, localPredictorMask, localPredictorSize, localThreshold, and gem5::mask().
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Updates the branch predictor to Not Taken if a BTB entry is invalid or not found.
branch_addr | The address of the branch to look up. |
bp_history | Pointer to any bp history state. |
Implements gem5::branch_prediction::BPredUnit.
Definition at line 169 of file tournament.cc.
References calcLocHistIdx(), globalHistory, historyRegisterMask, localHistoryTable, and localPredictorMask.
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inlineprivate |
Returns the local history index, given a branch address.
branch_addr | The 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().
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Returns if the branch should be taken or not, given a counter value.
count | The counter value. |
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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.
branch_addr | The address of the branch to look up. |
bp_history | Pointer that will be set to the BPHistory object. |
Implements gem5::branch_prediction::BPredUnit.
Definition at line 180 of file tournament.cc.
References calcLocHistIdx(), choiceCtrs, choiceHistoryMask, choiceThreshold, globalCtrs, gem5::branch_prediction::TournamentBP::BPHistory::globalHistory, globalHistory, globalHistoryMask, gem5::branch_prediction::TournamentBP::BPHistory::globalPredTaken, globalThreshold, gem5::branch_prediction::TournamentBP::BPHistory::globalUsed, localCtrs, gem5::branch_prediction::TournamentBP::BPHistory::localHistory, gem5::branch_prediction::TournamentBP::BPHistory::localHistoryIdx, localHistoryTable, localHistoryTableSize, localPredictorMask, gem5::branch_prediction::TournamentBP::BPHistory::localPredTaken, localThreshold, updateGlobalHistNotTaken(), updateGlobalHistTaken(), updateLocalHistNotTaken(), and updateLocalHistTaken().
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Restores the global branch history on a squash.
bp_history | Pointer 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.
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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.
bp_history | Pointer that will be set to the BPHistory object. |
Implements gem5::branch_prediction::BPredUnit.
Definition at line 241 of file tournament.cc.
References gem5::branch_prediction::TournamentBP::BPHistory::globalHistory, globalHistory, gem5::branch_prediction::TournamentBP::BPHistory::globalPredTaken, gem5::branch_prediction::TournamentBP::BPHistory::globalUsed, invalidPredictorIndex, gem5::branch_prediction::TournamentBP::BPHistory::localHistory, gem5::branch_prediction::TournamentBP::BPHistory::localHistoryIdx, gem5::branch_prediction::TournamentBP::BPHistory::localPredTaken, and updateGlobalHistTaken().
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virtual |
Updates the branch predictor with the actual result of a branch.
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 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.
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Updates global history as not taken.
Definition at line 145 of file tournament.cc.
References globalHistory, and historyRegisterMask.
Referenced by lookup().
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inlineprivate |
Updates global history as taken.
Definition at line 137 of file tournament.cc.
References globalHistory, and historyRegisterMask.
Referenced by lookup(), and uncondBranch().
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Updates local histories as not taken.
local_history_idx | The local history table entry that will be updated. |
Definition at line 161 of file tournament.cc.
References localHistoryTable.
Referenced by lookup().
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inlineprivate |
Updates local histories as taken.
local_history_idx | The local history table entry that will be updated. |
Definition at line 153 of file tournament.cc.
References localHistoryTable.
Referenced by lookup().
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Number of bits in the choice predictor's counters.
Definition at line 235 of file tournament.hh.
Referenced by TournamentBP().
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Array of counters that make up the choice predictor.
Definition at line 238 of file tournament.hh.
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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().
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Number of entries in the choice predictor.
Definition at line 232 of file tournament.hh.
Referenced by TournamentBP().
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Definition at line 245 of file tournament.hh.
Referenced by lookup(), and TournamentBP().
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Number of bits of the global predictor's counters.
Definition at line 205 of file tournament.hh.
Referenced by TournamentBP().
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Array of counters that make up the global predictor.
Definition at line 208 of file tournament.hh.
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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().
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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().
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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().
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Number of entries in the global predictor.
Definition at line 202 of file tournament.hh.
Referenced by TournamentBP().
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Definition at line 244 of file tournament.hh.
Referenced by lookup(), and TournamentBP().
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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().
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Flag for invalid predictor index.
Definition at line 179 of file tournament.hh.
Referenced by squash(), uncondBranch(), and update().
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Number of bits of the local predictor's counters.
Definition at line 187 of file tournament.hh.
Referenced by TournamentBP().
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Number of bits for each entry of the local history table.
Definition at line 199 of file tournament.hh.
Referenced by TournamentBP().
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Array of local history table entries.
Definition at line 193 of file tournament.hh.
Referenced by btbUpdate(), lookup(), squash(), TournamentBP(), update(), updateLocalHistNotTaken(), and updateLocalHistTaken().
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Number of entries in the local history table.
Definition at line 196 of file tournament.hh.
Referenced by calcLocHistIdx(), lookup(), TournamentBP(), and update().
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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().
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Number of counters in the local predictor.
Definition at line 181 of file tournament.hh.
Referenced by TournamentBP(), and update().
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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().