gem5/cpu/o3/tournament_pred.cc
Kevin Lim 248bd2bb62 Various branch predictor fixes/cleanup. It works more correctly now and supports both local and tournament predictors.
cpu/o3/2bit_local_pred.cc:
    Branch predictor cleanup/fixup.  Rename this to LocalBP.
cpu/o3/2bit_local_pred.hh:
    Rename to LocalBP, update to support changes to BPredUnit, include comments.
cpu/o3/alpha_cpu_builder.cc:
    Support extra parameters to the branch predictor.  Now it takes in a parameter to tell it which branch predictor it is using, the local or the tournament predictor.
cpu/o3/alpha_params.hh:
    Add in extra parameter for the branch predictor type.
cpu/o3/bpred_unit.cc:
    Branch predictor fixup/cleanup.  Rename it to BPredUnit.
cpu/o3/bpred_unit.hh:
    Branch predictor fixup/cleanup.  Now supports both the local and tournament predictors, and stores the branch predictor update state.
cpu/o3/bpred_unit_impl.hh:
    Branch predictor overhaul.  Now supports both the local and tournament predictors.
cpu/o3/cpu_policy.hh:
cpu/ozone/ozone_impl.hh:
cpu/ozone/simple_impl.hh:
    Reflect the class name change.
cpu/o3/decode_impl.hh:
    Be sure to set the predicted target as well so we don't squash twice.
cpu/o3/tournament_pred.cc:
cpu/o3/tournament_pred.hh:
    Fixes to the tournament predictor.
cpu/ozone/simple_params.hh:
    Include parameter for the branch predictor type.
python/m5/objects/AlphaFullCPU.py:
python/m5/objects/OzoneCPU.py:
    Include the parameter for the branch predictor type.

--HG--
extra : convert_revision : 34afebb3b40b47accb12558e439ee4cb03df5e64
2006-05-25 17:01:48 -04:00

291 lines
9.8 KiB
C++

/*
* Copyright (c) 2004-2006 The Regents of The University of Michigan
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions are
* met: redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer;
* redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution;
* neither the name of the copyright holders nor the names of its
* contributors may be used to endorse or promote products derived from
* this software without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
* A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
* OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
* SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
* LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
* DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
* THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
* OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/
#include "base/intmath.hh"
#include "cpu/o3/tournament_pred.hh"
TournamentBP::TournamentBP(unsigned _localPredictorSize,
unsigned _localCtrBits,
unsigned _localHistoryTableSize,
unsigned _localHistoryBits,
unsigned _globalPredictorSize,
unsigned _globalCtrBits,
unsigned _globalHistoryBits,
unsigned _choicePredictorSize,
unsigned _choiceCtrBits,
unsigned _instShiftAmt)
: localPredictorSize(_localPredictorSize),
localCtrBits(_localCtrBits),
localHistoryTableSize(_localHistoryTableSize),
localHistoryBits(_localHistoryBits),
globalPredictorSize(_globalPredictorSize),
globalCtrBits(_globalCtrBits),
globalHistoryBits(_globalHistoryBits),
choicePredictorSize(_globalPredictorSize),
choiceCtrBits(_choiceCtrBits),
instShiftAmt(_instShiftAmt)
{
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);
for (int i = 0; i < localHistoryTableSize; ++i)
localHistoryTable[i] = 0;
// 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);
for (int i = 0; i < globalPredictorSize; ++i)
globalCtrs[i].setBits(globalCtrBits);
//Clear the global history
globalHistory = 0;
// 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;
}
inline
unsigned
TournamentBP::calcLocHistIdx(Addr &branch_addr)
{
// Get low order bits after removing instruction offset.
return (branch_addr >> instShiftAmt) & (localHistoryTableSize - 1);
}
inline
void
TournamentBP::updateGlobalHistTaken()
{
globalHistory = (globalHistory << 1) | 1;
globalHistory = globalHistory & globalHistoryMask;
}
inline
void
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, void * &bp_history)
{
bool local_prediction;
unsigned local_history_idx;
unsigned local_predictor_idx;
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() > threshold;
//Lookup in the global predictor to get its branch prediction
global_prediction = globalCtrs[globalHistory].read() > threshold;
//Lookup in the choice predictor to see which one to use
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);
// globalCtrs[globalHistory].decrement();
// localCtrs[local_history_idx].decrement();
updateGlobalHistNotTaken();
return false;
}
} else {
if (local_prediction) {
// updateHistoriesTaken(local_history_idx);
// globalCtrs[globalHistory].increment();
// localCtrs[local_history_idx].increment();
updateGlobalHistTaken();
return true;
} else {
// updateHistoriesNotTaken(local_history_idx);
// globalCtrs[globalHistory].decrement();
// localCtrs[local_history_idx].decrement();
updateGlobalHistNotTaken();
return false;
}
}
}
void
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();
}
void
TournamentBP::update(Addr &branch_addr, bool taken, void *bp_history)
{
unsigned local_history_idx;
unsigned local_predictor_idx;
unsigned local_predictor_hist;
// Get the local predictor's current prediction
local_history_idx = calcLocHistIdx(branch_addr);
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;
}
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();
updateLocalHistTaken(local_history_idx);
} else {
localCtrs[local_predictor_idx].decrement();
globalCtrs[globalHistory].decrement();
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