BranchPredictor.py revision 13685:bb3377c81303 
1# Copyright (c) 2012 Mark D. Hill and David A. Wood
2# Copyright (c) 2015 The University of Wisconsin
3# All rights reserved.
4#
5# Redistribution and use in source and binary forms, with or without
6# modification, are permitted provided that the following conditions are
7# met: redistributions of source code must retain the above copyright
8# notice, this list of conditions and the following disclaimer;
9# redistributions in binary form must reproduce the above copyright
10# notice, this list of conditions and the following disclaimer in the
11# documentation and/or other materials provided with the distribution;
12# neither the name of the copyright holders nor the names of its
13# contributors may be used to endorse or promote products derived from
14# this software without specific prior written permission.
15#
16# THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
17# "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
18# LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
19# A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
20# OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
21# SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
22# LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
23# DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
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25# (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
26# OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
27#
28# Authors: Nilay Vaish and Dibakar Gope
29
30from m5.SimObject import SimObject
31from m5.params import *
32from m5.proxy import *
33
34class BranchPredictor(SimObject):
35    type = 'BranchPredictor'
36    cxx_class = 'BPredUnit'
37    cxx_header = "cpu/pred/bpred_unit.hh"
38    abstract = True
39
40    numThreads = Param.Unsigned(Parent.numThreads, "Number of threads")
41    BTBEntries = Param.Unsigned(4096, "Number of BTB entries")
42    BTBTagSize = Param.Unsigned(16, "Size of the BTB tags, in bits")
43    RASSize = Param.Unsigned(16, "RAS size")
44    instShiftAmt = Param.Unsigned(2, "Number of bits to shift instructions by")
45
46    useIndirect = Param.Bool(True, "Use indirect branch predictor")
47    indirectHashGHR = Param.Bool(True, "Hash branch predictor GHR")
48    indirectHashTargets = Param.Bool(True, "Hash path history targets")
49    indirectSets = Param.Unsigned(256, "Cache sets for indirect predictor")
50    indirectWays = Param.Unsigned(2, "Ways for indirect predictor")
51    indirectTagSize = Param.Unsigned(16, "Indirect target cache tag bits")
52    indirectPathLength = Param.Unsigned(3,
53        "Previous indirect targets to use for path history")
54
55
56
57class LocalBP(BranchPredictor):
58    type = 'LocalBP'
59    cxx_class = 'LocalBP'
60    cxx_header = "cpu/pred/2bit_local.hh"
61
62    localPredictorSize = Param.Unsigned(2048, "Size of local predictor")
63    localCtrBits = Param.Unsigned(2, "Bits per counter")
64
65
66class TournamentBP(BranchPredictor):
67    type = 'TournamentBP'
68    cxx_class = 'TournamentBP'
69    cxx_header = "cpu/pred/tournament.hh"
70
71    localPredictorSize = Param.Unsigned(2048, "Size of local predictor")
72    localCtrBits = Param.Unsigned(2, "Bits per counter")
73    localHistoryTableSize = Param.Unsigned(2048, "size of local history table")
74    globalPredictorSize = Param.Unsigned(8192, "Size of global predictor")
75    globalCtrBits = Param.Unsigned(2, "Bits per counter")
76    choicePredictorSize = Param.Unsigned(8192, "Size of choice predictor")
77    choiceCtrBits = Param.Unsigned(2, "Bits of choice counters")
78
79
80class BiModeBP(BranchPredictor):
81    type = 'BiModeBP'
82    cxx_class = 'BiModeBP'
83    cxx_header = "cpu/pred/bi_mode.hh"
84
85    globalPredictorSize = Param.Unsigned(8192, "Size of global predictor")
86    globalCtrBits = Param.Unsigned(2, "Bits per counter")
87    choicePredictorSize = Param.Unsigned(8192, "Size of choice predictor")
88    choiceCtrBits = Param.Unsigned(2, "Bits of choice counters")
89
90class TAGEBase(SimObject):
91    type = 'TAGEBase'
92    cxx_class = 'TAGEBase'
93    cxx_header = "cpu/pred/tage_base.hh"
94
95    numThreads = Param.Unsigned(Parent.numThreads, "Number of threads")
96    instShiftAmt = Param.Unsigned(Parent.instShiftAmt,
97        "Number of bits to shift instructions by")
98
99    nHistoryTables = Param.Unsigned(7, "Number of history tables")
100    minHist = Param.Unsigned(5, "Minimum history size of TAGE")
101    maxHist = Param.Unsigned(130, "Maximum history size of TAGE")
102
103    tagTableTagWidths = VectorParam.Unsigned(
104        [0, 9, 9, 10, 10, 11, 11, 12], "Tag size in TAGE tag tables")
105    logTagTableSizes = VectorParam.Int(
106        [13, 9, 9, 9, 9, 9, 9, 9], "Log2 of TAGE table sizes")
107    logRatioBiModalHystEntries = Param.Unsigned(2,
108        "Log num of prediction entries for a shared hysteresis bit " \
109        "for the Bimodal")
110
111    tagTableCounterBits = Param.Unsigned(3, "Number of tag table counter bits")
112    tagTableUBits = Param.Unsigned(2, "Number of tag table u bits")
113
114    histBufferSize = Param.Unsigned(2097152,
115            "A large number to track all branch histories(2MEntries default)")
116
117    pathHistBits = Param.Unsigned(16, "Path history size")
118    logUResetPeriod = Param.Unsigned(18,
119        "Log period in number of branches to reset TAGE useful counters")
120    numUseAltOnNa = Param.Unsigned(1, "Number of USE_ALT_ON_NA counters")
121    useAltOnNaBits = Param.Unsigned(4, "Size of the USE_ALT_ON_NA counter(s)")
122
123    maxNumAlloc = Param.Unsigned(1,
124        "Max number of TAGE entries allocted on mispredict")
125
126    # List of enabled TAGE tables. If empty, all are enabled
127    noSkip = VectorParam.Bool([], "Vector of enabled TAGE tables")
128
129    speculativeHistUpdate = Param.Bool(True,
130        "Use speculative update for histories")
131
132# TAGE branch predictor as described in https://www.jilp.org/vol8/v8paper1.pdf
133# The default sizes below are for the 8C-TAGE configuration (63.5 Kbits)
134class TAGE(BranchPredictor):
135    type = 'TAGE'
136    cxx_class = 'TAGE'
137    cxx_header = "cpu/pred/tage.hh"
138    tage = Param.TAGEBase(TAGEBase(), "Tage object")
139
140class LTAGE_TAGE(TAGEBase):
141    nHistoryTables = 12
142    minHist = 4
143    maxHist = 640
144    tagTableTagWidths = [0, 7, 7, 8, 8, 9, 10, 11, 12, 12, 13, 14, 15]
145    logTagTableSizes = [14, 10, 10, 11, 11, 11, 11, 10, 10, 10, 10, 9, 9]
146    logUResetPeriod = 19
147
148class LoopPredictor(SimObject):
149    type = 'LoopPredictor'
150    cxx_class = 'LoopPredictor'
151    cxx_header = 'cpu/pred/loop_predictor.hh'
152
153    logSizeLoopPred = Param.Unsigned(8, "Log size of the loop predictor")
154    withLoopBits = Param.Unsigned(7, "Size of the WITHLOOP counter")
155    loopTableAgeBits = Param.Unsigned(8, "Number of age bits per loop entry")
156    loopTableConfidenceBits = Param.Unsigned(2,
157            "Number of confidence bits per loop entry")
158    loopTableTagBits = Param.Unsigned(14, "Number of tag bits per loop entry")
159    loopTableIterBits = Param.Unsigned(14, "Nuber of iteration bits per loop")
160    logLoopTableAssoc = Param.Unsigned(2, "Log loop predictor associativity")
161
162    # Parameters for enabling modifications to the loop predictor
163    # They have been copied from TAGE-GSC-IMLI
164    # (http://www.irisa.fr/alf/downloads/seznec/TAGE-GSC-IMLI.tar)
165    #
166    # All of them should be disabled to match the original LTAGE implementation
167    # (http://hpca23.cse.tamu.edu/taco/camino/cbp2/cbp-src/realistic-seznec.h)
168
169    # Add speculation
170    useSpeculation = Param.Bool(False, "Use speculation")
171
172    # Add hashing for calculating the loop table index
173    useHashing = Param.Bool(False, "Use hashing")
174
175    # Add a direction bit to the loop table entries
176    useDirectionBit = Param.Bool(False, "Use direction info")
177
178    # If true, use random to decide whether to allocate or not, and only try
179    # with one entry
180    restrictAllocation = Param.Bool(False,
181        "Restrict the allocation conditions")
182
183    initialLoopIter = Param.Unsigned(1, "Initial iteration number")
184    initialLoopAge = Param.Unsigned(255, "Initial age value")
185    optionalAgeReset = Param.Bool(True,
186        "Reset age bits optionally in some cases")
187
188class TAGE_SC_L_TAGE(TAGEBase):
189    type = 'TAGE_SC_L_TAGE'
190    cxx_class = 'TAGE_SC_L_TAGE'
191    cxx_header = "cpu/pred/tage_sc_l.hh"
192    abstract = True
193    tagTableTagWidths = [0]
194    numUseAltOnNa = 16
195    pathHistBits = 27
196    maxNumAlloc = 2
197    logUResetPeriod = 10
198    useAltOnNaBits = 5
199    # TODO No speculation implemented as of now
200    speculativeHistUpdate = False
201
202    # This size does not set the final sizes of the tables (it is just used
203    # for some calculations)
204    # Instead, the number of TAGE entries comes from shortTagsTageEntries and
205    # longTagsTageEntries
206    logTagTableSize = Param.Unsigned("Log size of each tag table")
207
208    shortTagsTageFactor = Param.Unsigned(
209        "Factor for calculating the total number of short tags TAGE entries")
210
211    longTagsTageFactor = Param.Unsigned(
212        "Factor for calculating the total number of long tags TAGE entries")
213
214    shortTagsSize = Param.Unsigned(8, "Size of the short tags")
215
216    longTagsSize = Param.Unsigned("Size of the long tags")
217
218    firstLongTagTable = Param.Unsigned("First table with long tags")
219
220    truncatePathHist = Param.Bool(True,
221        "Truncate the path history to its configured size")
222
223
224class TAGE_SC_L_TAGE_64KB(TAGE_SC_L_TAGE):
225    type = 'TAGE_SC_L_TAGE_64KB'
226    cxx_class = 'TAGE_SC_L_TAGE_64KB'
227    cxx_header = "cpu/pred/tage_sc_l_64KB.hh"
228    nHistoryTables = 36
229
230    minHist = 6
231    maxHist = 3000
232
233    tagTableUBits = 1
234
235    logTagTableSizes = [13]
236
237    # This is used to handle the 2-way associativity
238    # (all odd entries are set to one, and if the corresponding even entry
239    # is set to one, then there is a 2-way associativity for this pair)
240    # Entry 0 is for the bimodal and it is ignored
241    # Note: For this implementation, some odd entries are also set to 0 to save
242    # some bits
243    noSkip = [0,0,1,0,0,0,1,0,0,1,1,1,1,1,1,1,1,1,1,
244                1,1,1,1,0,1,0,1,0,1,0,0,0,1,0,0,0,1]
245
246    logTagTableSize = 10
247    shortTagsTageFactor = 10
248    longTagsTageFactor = 20
249
250    longTagsSize = 12
251
252    firstLongTagTable = 13
253
254class TAGE_SC_L_TAGE_8KB(TAGE_SC_L_TAGE):
255    type = 'TAGE_SC_L_TAGE_8KB'
256    cxx_class = 'TAGE_SC_L_TAGE_8KB'
257    cxx_header = "cpu/pred/tage_sc_l_8KB.hh"
258
259    nHistoryTables = 30
260
261    minHist = 4
262    maxHist = 1000
263
264    logTagTableSize = 7
265    shortTagsTageFactor = 9
266    longTagsTageFactor = 17
267    longTagsSize = 12
268
269    logTagTableSizes = [12]
270
271    firstLongTagTable = 11
272
273    truncatePathHist = False
274
275    noSkip = [0,0,1,0,1,0,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,0,1,0,1,0,1,0,1,0,1]
276
277    tagTableUBits = 2
278
279# LTAGE branch predictor as described in
280# https://www.irisa.fr/caps/people/seznec/L-TAGE.pdf
281# It is basically a TAGE predictor plus a loop predictor
282# The differnt TAGE sizes are updated according to the paper values (256 Kbits)
283class LTAGE(TAGE):
284    type = 'LTAGE'
285    cxx_class = 'LTAGE'
286    cxx_header = "cpu/pred/ltage.hh"
287
288    tage = LTAGE_TAGE()
289
290    loop_predictor = Param.LoopPredictor(LoopPredictor(), "Loop predictor")
291
292class TAGE_SC_L_LoopPredictor(LoopPredictor):
293    type = 'TAGE_SC_L_LoopPredictor'
294    cxx_class  = 'TAGE_SC_L_LoopPredictor'
295    cxx_header = "cpu/pred/tage_sc_l.hh"
296    loopTableAgeBits = 4
297    loopTableConfidenceBits = 4
298    loopTableTagBits = 10
299    loopTableIterBits = 10
300    useSpeculation = False
301    useHashing = True
302    useDirectionBit = True
303    restrictAllocation = True
304    initialLoopIter = 0
305    initialLoopAge = 7
306    optionalAgeReset = False
307
308class StatisticalCorrector(SimObject):
309    type = 'StatisticalCorrector'
310    cxx_class  = 'StatisticalCorrector'
311    cxx_header = "cpu/pred/statistical_corrector.hh"
312    abstract = True
313
314    # Statistical corrector parameters
315
316    numEntriesFirstLocalHistories = Param.Unsigned(
317        "Number of entries for first local histories")
318
319    bwnb = Param.Unsigned("Num global backward branch GEHL lengths")
320    bwm = VectorParam.Int("Global backward branch GEHL lengths")
321    logBwnb = Param.Unsigned("Log num of global backward branch GEHL entries")
322
323    lnb = Param.Unsigned("Num first local history GEHL lenghts")
324    lm = VectorParam.Int("First local history GEHL lengths")
325    logLnb = Param.Unsigned("Log number of first local history GEHL entries")
326
327    inb = Param.Unsigned(1, "Num IMLI GEHL lenghts")
328    im = VectorParam.Int([8], "IMLI history GEHL lengths")
329    logInb = Param.Unsigned("Log number of IMLI GEHL entries")
330
331    logBias = Param.Unsigned("Log size of Bias tables")
332
333    logSizeUp = Param.Unsigned(6,
334        "Log size of update threshold counters tables")
335
336    chooserConfWidth = Param.Unsigned(7,
337        "Number of bits for the chooser counters")
338
339    updateThresholdWidth = Param.Unsigned(12,
340        "Number of bits for the update threshold counter")
341
342    pUpdateThresholdWidth = Param.Unsigned(8,
343        "Number of bits for the pUpdate threshold counters")
344
345    extraWeightsWidth = Param.Unsigned(6,
346        "Number of bits for the extra weights")
347
348    scCountersWidth = Param.Unsigned(6, "Statistical corrector counters width")
349
350# TAGE-SC-L branch predictor as desribed in
351# https://www.jilp.org/cbp2016/paper/AndreSeznecLimited.pdf
352# It is a modified LTAGE predictor plus a statistical corrector predictor
353# The TAGE modifications include bank interleaving and partial associativity
354# Two different sizes are proposed in the paper:
355# 8KB => See TAGE_SC_L_8KB below
356# 64KB => See TAGE_SC_L_64KB below
357# The TAGE_SC_L_8KB and TAGE_SC_L_64KB classes differ not only on the values
358# of some parameters, but also in some implementation details
359# Given this, the TAGE_SC_L class is left abstract
360# Note that as it is now, this branch predictor does not handle any type
361# of speculation: All the structures/histories are updated at commit time
362class TAGE_SC_L(LTAGE):
363    type = 'TAGE_SC_L'
364    cxx_class = 'TAGE_SC_L'
365    cxx_header = "cpu/pred/tage_sc_l.hh"
366    abstract = True
367
368    statistical_corrector = Param.StatisticalCorrector(
369        "Statistical Corrector")
370
371class TAGE_SC_L_64KB_LoopPredictor(TAGE_SC_L_LoopPredictor):
372    logSizeLoopPred = 5
373
374class TAGE_SC_L_8KB_LoopPredictor(TAGE_SC_L_LoopPredictor):
375    logSizeLoopPred = 3
376
377class TAGE_SC_L_64KB_StatisticalCorrector(StatisticalCorrector):
378    type = 'TAGE_SC_L_64KB_StatisticalCorrector'
379    cxx_class  = 'TAGE_SC_L_64KB_StatisticalCorrector'
380    cxx_header = "cpu/pred/tage_sc_l_64KB.hh"
381
382    pnb = Param.Unsigned(3, "Num variation global branch GEHL lengths")
383    pm = VectorParam.Int([25, 16, 9], "Variation global branch GEHL lengths")
384    logPnb = Param.Unsigned(9,
385        "Log number of variation global branch GEHL entries")
386
387    snb = Param.Unsigned(3, "Num second local history GEHL lenghts")
388    sm = VectorParam.Int([16, 11, 6], "Second local history GEHL lengths")
389    logSnb = Param.Unsigned(9,
390        "Log number of second local history GEHL entries")
391
392    tnb = Param.Unsigned(2, "Num third local history GEHL lenghts")
393    tm = VectorParam.Int([9, 4], "Third local history GEHL lengths")
394    logTnb = Param.Unsigned(10,
395        "Log number of third local history GEHL entries")
396
397    imnb = Param.Unsigned(2, "Num second IMLI GEHL lenghts")
398    imm = VectorParam.Int([10, 4], "Second IMLI history GEHL lengths")
399    logImnb = Param.Unsigned(9, "Log number of second IMLI GEHL entries")
400
401    numEntriesSecondLocalHistories = Param.Unsigned(16,
402        "Number of entries for second local histories")
403    numEntriesThirdLocalHistories = Param.Unsigned(16,
404        "Number of entries for second local histories")
405
406    numEntriesFirstLocalHistories = 256
407
408    logBias = 8
409
410    bwnb = 3
411    bwm = [40, 24, 10]
412    logBwnb = 10
413
414    lnb = 3
415    lm = [11, 6, 3]
416    logLnb = 10
417
418    logInb = 8
419
420class TAGE_SC_L_8KB_StatisticalCorrector(StatisticalCorrector):
421    type = 'TAGE_SC_L_8KB_StatisticalCorrector'
422    cxx_class  = 'TAGE_SC_L_8KB_StatisticalCorrector'
423    cxx_header = "cpu/pred/tage_sc_l_8KB.hh"
424    gnb = Param.Unsigned(2, "Num global branch GEHL lengths")
425    gm = VectorParam.Int([6, 3], "Global branch GEHL lengths")
426    logGnb = Param.Unsigned(7, "Log number of global branch GEHL entries")
427
428    numEntriesFirstLocalHistories = 64
429
430    logBias = 7
431
432    bwnb = 2
433    logBwnb = 7
434    bwm = [16, 8]
435
436    lnb = 2
437    logLnb = 7
438    lm = [6, 3]
439
440    logInb = 7
441
442# 64KB TAGE-SC-L branch predictor as described in
443# http://www.jilp.org/cbp2016/paper/AndreSeznecLimited.pdf
444class TAGE_SC_L_64KB(TAGE_SC_L):
445    type = 'TAGE_SC_L_64KB'
446    cxx_class = 'TAGE_SC_L_64KB'
447    cxx_header = "cpu/pred/tage_sc_l_64KB.hh"
448
449    tage = TAGE_SC_L_TAGE_64KB()
450    loop_predictor = TAGE_SC_L_64KB_LoopPredictor()
451    statistical_corrector = TAGE_SC_L_64KB_StatisticalCorrector()
452
453# 8KB TAGE-SC-L branch predictor as described in
454# http://www.jilp.org/cbp2016/paper/AndreSeznecLimited.pdf
455class TAGE_SC_L_8KB(TAGE_SC_L):
456    type = 'TAGE_SC_L_8KB'
457    cxx_class = 'TAGE_SC_L_8KB'
458    cxx_header = "cpu/pred/tage_sc_l_8KB.hh"
459
460    tage = TAGE_SC_L_TAGE_8KB()
461    loop_predictor = TAGE_SC_L_8KB_LoopPredictor()
462    statistical_corrector = TAGE_SC_L_8KB_StatisticalCorrector()
463