BranchPredictor.py revision 13957:25e9c77a8a99 
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 IndirectPredictor(SimObject):
35    type = 'IndirectPredictor'
36    cxx_class = 'IndirectPredictor'
37    cxx_header = "cpu/pred/indirect.hh"
38    abstract = True
39
40    numThreads = Param.Unsigned(Parent.numThreads, "Number of threads")
41
42class SimpleIndirectPredictor(IndirectPredictor):
43    type = 'SimpleIndirectPredictor'
44    cxx_class = 'SimpleIndirectPredictor'
45    cxx_header = "cpu/pred/simple_indirect.hh"
46
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    indirectGHRBits = Param.Unsigned(13, "Indirect GHR number of bits")
55    instShiftAmt = Param.Unsigned(2, "Number of bits to shift instructions by")
56
57class BranchPredictor(SimObject):
58    type = 'BranchPredictor'
59    cxx_class = 'BPredUnit'
60    cxx_header = "cpu/pred/bpred_unit.hh"
61    abstract = True
62
63    numThreads = Param.Unsigned(Parent.numThreads, "Number of threads")
64    BTBEntries = Param.Unsigned(4096, "Number of BTB entries")
65    BTBTagSize = Param.Unsigned(16, "Size of the BTB tags, in bits")
66    RASSize = Param.Unsigned(16, "RAS size")
67    instShiftAmt = Param.Unsigned(2, "Number of bits to shift instructions by")
68
69    indirectBranchPred = Param.IndirectPredictor(SimpleIndirectPredictor(),
70      "Indirect branch predictor, set to NULL to disable indirect predictions")
71
72class LocalBP(BranchPredictor):
73    type = 'LocalBP'
74    cxx_class = 'LocalBP'
75    cxx_header = "cpu/pred/2bit_local.hh"
76
77    localPredictorSize = Param.Unsigned(2048, "Size of local predictor")
78    localCtrBits = Param.Unsigned(2, "Bits per counter")
79
80
81class TournamentBP(BranchPredictor):
82    type = 'TournamentBP'
83    cxx_class = 'TournamentBP'
84    cxx_header = "cpu/pred/tournament.hh"
85
86    localPredictorSize = Param.Unsigned(2048, "Size of local predictor")
87    localCtrBits = Param.Unsigned(2, "Bits per counter")
88    localHistoryTableSize = Param.Unsigned(2048, "size of local history table")
89    globalPredictorSize = Param.Unsigned(8192, "Size of global predictor")
90    globalCtrBits = Param.Unsigned(2, "Bits per counter")
91    choicePredictorSize = Param.Unsigned(8192, "Size of choice predictor")
92    choiceCtrBits = Param.Unsigned(2, "Bits of choice counters")
93
94
95class BiModeBP(BranchPredictor):
96    type = 'BiModeBP'
97    cxx_class = 'BiModeBP'
98    cxx_header = "cpu/pred/bi_mode.hh"
99
100    globalPredictorSize = Param.Unsigned(8192, "Size of global predictor")
101    globalCtrBits = Param.Unsigned(2, "Bits per counter")
102    choicePredictorSize = Param.Unsigned(8192, "Size of choice predictor")
103    choiceCtrBits = Param.Unsigned(2, "Bits of choice counters")
104
105class TAGEBase(SimObject):
106    type = 'TAGEBase'
107    cxx_class = 'TAGEBase'
108    cxx_header = "cpu/pred/tage_base.hh"
109
110    numThreads = Param.Unsigned(Parent.numThreads, "Number of threads")
111    instShiftAmt = Param.Unsigned(Parent.instShiftAmt,
112        "Number of bits to shift instructions by")
113
114    nHistoryTables = Param.Unsigned(7, "Number of history tables")
115    minHist = Param.Unsigned(5, "Minimum history size of TAGE")
116    maxHist = Param.Unsigned(130, "Maximum history size of TAGE")
117
118    tagTableTagWidths = VectorParam.Unsigned(
119        [0, 9, 9, 10, 10, 11, 11, 12], "Tag size in TAGE tag tables")
120    logTagTableSizes = VectorParam.Int(
121        [13, 9, 9, 9, 9, 9, 9, 9], "Log2 of TAGE table sizes")
122    logRatioBiModalHystEntries = Param.Unsigned(2,
123        "Log num of prediction entries for a shared hysteresis bit " \
124        "for the Bimodal")
125
126    tagTableCounterBits = Param.Unsigned(3, "Number of tag table counter bits")
127    tagTableUBits = Param.Unsigned(2, "Number of tag table u bits")
128
129    histBufferSize = Param.Unsigned(2097152,
130            "A large number to track all branch histories(2MEntries default)")
131
132    pathHistBits = Param.Unsigned(16, "Path history size")
133    logUResetPeriod = Param.Unsigned(18,
134        "Log period in number of branches to reset TAGE useful counters")
135    numUseAltOnNa = Param.Unsigned(1, "Number of USE_ALT_ON_NA counters")
136    useAltOnNaBits = Param.Unsigned(4, "Size of the USE_ALT_ON_NA counter(s)")
137
138    maxNumAlloc = Param.Unsigned(1,
139        "Max number of TAGE entries allocted on mispredict")
140
141    # List of enabled TAGE tables. If empty, all are enabled
142    noSkip = VectorParam.Bool([], "Vector of enabled TAGE tables")
143
144    speculativeHistUpdate = Param.Bool(True,
145        "Use speculative update for histories")
146
147# TAGE branch predictor as described in https://www.jilp.org/vol8/v8paper1.pdf
148# The default sizes below are for the 8C-TAGE configuration (63.5 Kbits)
149class TAGE(BranchPredictor):
150    type = 'TAGE'
151    cxx_class = 'TAGE'
152    cxx_header = "cpu/pred/tage.hh"
153    tage = Param.TAGEBase(TAGEBase(), "Tage object")
154
155class LTAGE_TAGE(TAGEBase):
156    nHistoryTables = 12
157    minHist = 4
158    maxHist = 640
159    tagTableTagWidths = [0, 7, 7, 8, 8, 9, 10, 11, 12, 12, 13, 14, 15]
160    logTagTableSizes = [14, 10, 10, 11, 11, 11, 11, 10, 10, 10, 10, 9, 9]
161    logUResetPeriod = 19
162
163class LoopPredictor(SimObject):
164    type = 'LoopPredictor'
165    cxx_class = 'LoopPredictor'
166    cxx_header = 'cpu/pred/loop_predictor.hh'
167
168    logSizeLoopPred = Param.Unsigned(8, "Log size of the loop predictor")
169    withLoopBits = Param.Unsigned(7, "Size of the WITHLOOP counter")
170    loopTableAgeBits = Param.Unsigned(8, "Number of age bits per loop entry")
171    loopTableConfidenceBits = Param.Unsigned(2,
172            "Number of confidence bits per loop entry")
173    loopTableTagBits = Param.Unsigned(14, "Number of tag bits per loop entry")
174    loopTableIterBits = Param.Unsigned(14, "Nuber of iteration bits per loop")
175    logLoopTableAssoc = Param.Unsigned(2, "Log loop predictor associativity")
176
177    # Parameters for enabling modifications to the loop predictor
178    # They have been copied from TAGE-GSC-IMLI
179    # (http://www.irisa.fr/alf/downloads/seznec/TAGE-GSC-IMLI.tar)
180    #
181    # All of them should be disabled to match the original LTAGE implementation
182    # (http://hpca23.cse.tamu.edu/taco/camino/cbp2/cbp-src/realistic-seznec.h)
183
184    # Add speculation
185    useSpeculation = Param.Bool(False, "Use speculation")
186
187    # Add hashing for calculating the loop table index
188    useHashing = Param.Bool(False, "Use hashing")
189
190    # Add a direction bit to the loop table entries
191    useDirectionBit = Param.Bool(False, "Use direction info")
192
193    # If true, use random to decide whether to allocate or not, and only try
194    # with one entry
195    restrictAllocation = Param.Bool(False,
196        "Restrict the allocation conditions")
197
198    initialLoopIter = Param.Unsigned(1, "Initial iteration number")
199    initialLoopAge = Param.Unsigned(255, "Initial age value")
200    optionalAgeReset = Param.Bool(True,
201        "Reset age bits optionally in some cases")
202
203class TAGE_SC_L_TAGE(TAGEBase):
204    type = 'TAGE_SC_L_TAGE'
205    cxx_class = 'TAGE_SC_L_TAGE'
206    cxx_header = "cpu/pred/tage_sc_l.hh"
207    abstract = True
208    tagTableTagWidths = [0]
209    numUseAltOnNa = 16
210    pathHistBits = 27
211    maxNumAlloc = 2
212    logUResetPeriod = 10
213    useAltOnNaBits = 5
214    # TODO No speculation implemented as of now
215    speculativeHistUpdate = False
216
217    # This size does not set the final sizes of the tables (it is just used
218    # for some calculations)
219    # Instead, the number of TAGE entries comes from shortTagsTageEntries and
220    # longTagsTageEntries
221    logTagTableSize = Param.Unsigned("Log size of each tag table")
222
223    shortTagsTageFactor = Param.Unsigned(
224        "Factor for calculating the total number of short tags TAGE entries")
225
226    longTagsTageFactor = Param.Unsigned(
227        "Factor for calculating the total number of long tags TAGE entries")
228
229    shortTagsSize = Param.Unsigned(8, "Size of the short tags")
230
231    longTagsSize = Param.Unsigned("Size of the long tags")
232
233    firstLongTagTable = Param.Unsigned("First table with long tags")
234
235    truncatePathHist = Param.Bool(True,
236        "Truncate the path history to its configured size")
237
238
239class TAGE_SC_L_TAGE_64KB(TAGE_SC_L_TAGE):
240    type = 'TAGE_SC_L_TAGE_64KB'
241    cxx_class = 'TAGE_SC_L_TAGE_64KB'
242    cxx_header = "cpu/pred/tage_sc_l_64KB.hh"
243    nHistoryTables = 36
244
245    minHist = 6
246    maxHist = 3000
247
248    tagTableUBits = 1
249
250    logTagTableSizes = [13]
251
252    # This is used to handle the 2-way associativity
253    # (all odd entries are set to one, and if the corresponding even entry
254    # is set to one, then there is a 2-way associativity for this pair)
255    # Entry 0 is for the bimodal and it is ignored
256    # Note: For this implementation, some odd entries are also set to 0 to save
257    # some bits
258    noSkip = [0,0,1,0,0,0,1,0,0,1,1,1,1,1,1,1,1,1,1,
259                1,1,1,1,0,1,0,1,0,1,0,0,0,1,0,0,0,1]
260
261    logTagTableSize = 10
262    shortTagsTageFactor = 10
263    longTagsTageFactor = 20
264
265    longTagsSize = 12
266
267    firstLongTagTable = 13
268
269class TAGE_SC_L_TAGE_8KB(TAGE_SC_L_TAGE):
270    type = 'TAGE_SC_L_TAGE_8KB'
271    cxx_class = 'TAGE_SC_L_TAGE_8KB'
272    cxx_header = "cpu/pred/tage_sc_l_8KB.hh"
273
274    nHistoryTables = 30
275
276    minHist = 4
277    maxHist = 1000
278
279    logTagTableSize = 7
280    shortTagsTageFactor = 9
281    longTagsTageFactor = 17
282    longTagsSize = 12
283
284    logTagTableSizes = [12]
285
286    firstLongTagTable = 11
287
288    truncatePathHist = False
289
290    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]
291
292    tagTableUBits = 2
293
294# LTAGE branch predictor as described in
295# https://www.irisa.fr/caps/people/seznec/L-TAGE.pdf
296# It is basically a TAGE predictor plus a loop predictor
297# The differnt TAGE sizes are updated according to the paper values (256 Kbits)
298class LTAGE(TAGE):
299    type = 'LTAGE'
300    cxx_class = 'LTAGE'
301    cxx_header = "cpu/pred/ltage.hh"
302
303    tage = LTAGE_TAGE()
304
305    loop_predictor = Param.LoopPredictor(LoopPredictor(), "Loop predictor")
306
307class TAGE_SC_L_LoopPredictor(LoopPredictor):
308    type = 'TAGE_SC_L_LoopPredictor'
309    cxx_class  = 'TAGE_SC_L_LoopPredictor'
310    cxx_header = "cpu/pred/tage_sc_l.hh"
311    loopTableAgeBits = 4
312    loopTableConfidenceBits = 4
313    loopTableTagBits = 10
314    loopTableIterBits = 10
315    useSpeculation = False
316    useHashing = True
317    useDirectionBit = True
318    restrictAllocation = True
319    initialLoopIter = 0
320    initialLoopAge = 7
321    optionalAgeReset = False
322
323class StatisticalCorrector(SimObject):
324    type = 'StatisticalCorrector'
325    cxx_class  = 'StatisticalCorrector'
326    cxx_header = "cpu/pred/statistical_corrector.hh"
327    abstract = True
328
329    # Statistical corrector parameters
330
331    numEntriesFirstLocalHistories = Param.Unsigned(
332        "Number of entries for first local histories")
333
334    bwnb = Param.Unsigned("Num global backward branch GEHL lengths")
335    bwm = VectorParam.Int("Global backward branch GEHL lengths")
336    logBwnb = Param.Unsigned("Log num of global backward branch GEHL entries")
337
338    lnb = Param.Unsigned("Num first local history GEHL lenghts")
339    lm = VectorParam.Int("First local history GEHL lengths")
340    logLnb = Param.Unsigned("Log number of first local history GEHL entries")
341
342    inb = Param.Unsigned(1, "Num IMLI GEHL lenghts")
343    im = VectorParam.Int([8], "IMLI history GEHL lengths")
344    logInb = Param.Unsigned("Log number of IMLI GEHL entries")
345
346    logBias = Param.Unsigned("Log size of Bias tables")
347
348    logSizeUp = Param.Unsigned(6,
349        "Log size of update threshold counters tables")
350
351    chooserConfWidth = Param.Unsigned(7,
352        "Number of bits for the chooser counters")
353
354    updateThresholdWidth = Param.Unsigned(12,
355        "Number of bits for the update threshold counter")
356
357    pUpdateThresholdWidth = Param.Unsigned(8,
358        "Number of bits for the pUpdate threshold counters")
359
360    extraWeightsWidth = Param.Unsigned(6,
361        "Number of bits for the extra weights")
362
363    scCountersWidth = Param.Unsigned(6, "Statistical corrector counters width")
364
365# TAGE-SC-L branch predictor as desribed in
366# https://www.jilp.org/cbp2016/paper/AndreSeznecLimited.pdf
367# It is a modified LTAGE predictor plus a statistical corrector predictor
368# The TAGE modifications include bank interleaving and partial associativity
369# Two different sizes are proposed in the paper:
370# 8KB => See TAGE_SC_L_8KB below
371# 64KB => See TAGE_SC_L_64KB below
372# The TAGE_SC_L_8KB and TAGE_SC_L_64KB classes differ not only on the values
373# of some parameters, but also in some implementation details
374# Given this, the TAGE_SC_L class is left abstract
375# Note that as it is now, this branch predictor does not handle any type
376# of speculation: All the structures/histories are updated at commit time
377class TAGE_SC_L(LTAGE):
378    type = 'TAGE_SC_L'
379    cxx_class = 'TAGE_SC_L'
380    cxx_header = "cpu/pred/tage_sc_l.hh"
381    abstract = True
382
383    statistical_corrector = Param.StatisticalCorrector(
384        "Statistical Corrector")
385
386class TAGE_SC_L_64KB_LoopPredictor(TAGE_SC_L_LoopPredictor):
387    logSizeLoopPred = 5
388
389class TAGE_SC_L_8KB_LoopPredictor(TAGE_SC_L_LoopPredictor):
390    logSizeLoopPred = 3
391
392class TAGE_SC_L_64KB_StatisticalCorrector(StatisticalCorrector):
393    type = 'TAGE_SC_L_64KB_StatisticalCorrector'
394    cxx_class  = 'TAGE_SC_L_64KB_StatisticalCorrector'
395    cxx_header = "cpu/pred/tage_sc_l_64KB.hh"
396
397    pnb = Param.Unsigned(3, "Num variation global branch GEHL lengths")
398    pm = VectorParam.Int([25, 16, 9], "Variation global branch GEHL lengths")
399    logPnb = Param.Unsigned(9,
400        "Log number of variation global branch GEHL entries")
401
402    snb = Param.Unsigned(3, "Num second local history GEHL lenghts")
403    sm = VectorParam.Int([16, 11, 6], "Second local history GEHL lengths")
404    logSnb = Param.Unsigned(9,
405        "Log number of second local history GEHL entries")
406
407    tnb = Param.Unsigned(2, "Num third local history GEHL lenghts")
408    tm = VectorParam.Int([9, 4], "Third local history GEHL lengths")
409    logTnb = Param.Unsigned(10,
410        "Log number of third local history GEHL entries")
411
412    imnb = Param.Unsigned(2, "Num second IMLI GEHL lenghts")
413    imm = VectorParam.Int([10, 4], "Second IMLI history GEHL lengths")
414    logImnb = Param.Unsigned(9, "Log number of second IMLI GEHL entries")
415
416    numEntriesSecondLocalHistories = Param.Unsigned(16,
417        "Number of entries for second local histories")
418    numEntriesThirdLocalHistories = Param.Unsigned(16,
419        "Number of entries for second local histories")
420
421    numEntriesFirstLocalHistories = 256
422
423    logBias = 8
424
425    bwnb = 3
426    bwm = [40, 24, 10]
427    logBwnb = 10
428
429    lnb = 3
430    lm = [11, 6, 3]
431    logLnb = 10
432
433    logInb = 8
434
435class TAGE_SC_L_8KB_StatisticalCorrector(StatisticalCorrector):
436    type = 'TAGE_SC_L_8KB_StatisticalCorrector'
437    cxx_class  = 'TAGE_SC_L_8KB_StatisticalCorrector'
438    cxx_header = "cpu/pred/tage_sc_l_8KB.hh"
439    gnb = Param.Unsigned(2, "Num global branch GEHL lengths")
440    gm = VectorParam.Int([6, 3], "Global branch GEHL lengths")
441    logGnb = Param.Unsigned(7, "Log number of global branch GEHL entries")
442
443    numEntriesFirstLocalHistories = 64
444
445    logBias = 7
446
447    bwnb = 2
448    logBwnb = 7
449    bwm = [16, 8]
450
451    lnb = 2
452    logLnb = 7
453    lm = [6, 3]
454
455    logInb = 7
456
457# 64KB TAGE-SC-L branch predictor as described in
458# http://www.jilp.org/cbp2016/paper/AndreSeznecLimited.pdf
459class TAGE_SC_L_64KB(TAGE_SC_L):
460    type = 'TAGE_SC_L_64KB'
461    cxx_class = 'TAGE_SC_L_64KB'
462    cxx_header = "cpu/pred/tage_sc_l_64KB.hh"
463
464    tage = TAGE_SC_L_TAGE_64KB()
465    loop_predictor = TAGE_SC_L_64KB_LoopPredictor()
466    statistical_corrector = TAGE_SC_L_64KB_StatisticalCorrector()
467
468# 8KB TAGE-SC-L branch predictor as described in
469# http://www.jilp.org/cbp2016/paper/AndreSeznecLimited.pdf
470class TAGE_SC_L_8KB(TAGE_SC_L):
471    type = 'TAGE_SC_L_8KB'
472    cxx_class = 'TAGE_SC_L_8KB'
473    cxx_header = "cpu/pred/tage_sc_l_8KB.hh"
474
475    tage = TAGE_SC_L_TAGE_8KB()
476    loop_predictor = TAGE_SC_L_8KB_LoopPredictor()
477    statistical_corrector = TAGE_SC_L_8KB_StatisticalCorrector()
478