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Branch Predictor Tweaks #316

Merged

abejgonzalez merged 37 commits into master from bpd-tweaks-2

Jul 12, 2019

Contributor

bkorpan commented Jul 5, 2019

Type of change: bug fix | other enhancement

Impact: rtl refactoring

Development Phase: implementation

Release Notes
A collection of tweaks to make BOOM's branch predictor perform at a reasonable level.

bkorpan added enhancement performance bug labels

bkorpan force-pushed the bpd-tweaks-2 branch 4 times, most recently from 8273d52 to 84ceb44 Compare

July 6, 2019 17:04

abejgonzalez reviewed

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src/main/scala/bpu/bpd/gshare/gshare.scala Show resolved Hide resolved

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bkorpan added 12 commits

July 9, 2019 17:40


          [gshare] Only update counter table on mispredicts.


          [gshare] Use a counter update function which uses all 4 states while …

3c7f608

…only updating upon mispredicts.


          [config] Fixed SmallBoomConfig FTQ sizing.

56fe9bc


          [config] Specify a btb for SmallBoomConfig.

f10d590


          [microop] Added cfi_idx field to MicroOp.

16b07e7


          [exu] Replaced pc_lob field and getCfiIdx function with cfi_idx field…

ad399a1

… in BrResolutionInfo.


          [ifu] Don't perform an F3 (F4) btb update unless F4 is valid.

55f9318


          [gshare] Do indexing on the granularity of ICache banks.

492cc69


          [bpu] Reenabled RAS. Only pushes calls onto the stack in F3 for now.

ee1dc83


          [branch-checker] Fixed return address calculation.

4bd5dc4


          [btb] Remember if a branch was compressed.

2fd232c


          [bpu] Let the BTB push calls onto the RAS.

f897ca3

bkorpan force-pushed the bpd-tweaks-2 branch 2 times, most recently from b618454 to 642bc2b Compare

July 10, 2019 18:23

bkorpan added 4 commits

July 11, 2019 14:56


          [ifu] Only perform an F3 BTB update when an earlier jr has not been s…

f9196fe

…een.


          [btb] Have the BTB track whether its CFI was an edge instruction.

08fc91e


          [ifu] Make sure BTB updates done by the BPD indicate if the CFI was c…

7ab520c

…ompressed or straddling the fetch bundle edge.


          [gshare] Added GShareEntry bundle.

83ac2fe

bkorpan added 19 commits

July 11, 2019 14:56


          [gshare] Added getUpdated function to GShareEntry.

dccab6b


          [gshare] Added getTakens function to GShareEntry.

00af199


          [gshare] Updated logic from old row system to new entry system.

148f8a0


          [gshare] Updated index hash.

d735888


          [gshare] Reenabled counter strengthening updates.

893dca9


          [bpu] Tweaked path history function.

593dca3


          [bpu] Fixed history update.

13c2c1b


          [gshare] Improved index hash.

4d7b12e


          [gshare] Don't hash the PC low order bits into the high order bits of…

96a3c41

… the index, as this tends to be a source of 'unfortunate coincidences' w.r.t. hashing collisions when training a loop.


          [ras] Prevent the ras from performing an update while the backing pre…

96b7418

…dictor is redirecting. This seems fairly common.


          [ras] Also prevent btb-based updates when the backing predictor is pl…

5c4700e

…anning to redirect the next cycle.


          [fetchmonitor] Fixed assert typo.

41d5b88


          [btb-sa] Modified index hash to improve utilization.

c264bbd


          [bpd] Remove bankBytes parameter from bpd/gshare as it is no longer n…

493bac7

…ecessary.


          [bim] Pass bankBytes into the bimodal table and use it to choose an i…

da1fa6e

…ndex.


          [gshare] Clarified behavior of getUpdatedEntry.

ed92b35


          [bpu] Style tweaks.

08a770e


          [gshare] Tweaked getUpdated logic.

65e457c


          [tage] Tweaked TAGE index hash.

68eff02

bkorpan force-pushed the bpd-tweaks-2 branch 2 times, most recently from a830caa to 673c2b3 Compare

July 12, 2019 00:35

bkorpan added 2 commits

July 11, 2019 17:49


          [ifu] Simplified f3_bundle_mask generation.

65c4b7d


          [ifu] Only do a BTB update if r_f4_req is valid.

6b398f0

bkorpan force-pushed the bpd-tweaks-2 branch 2 times, most recently from a9543e6 to 6b398f0 Compare

July 12, 2019 00:52

abejgonzalez approved these changes

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Contributor

abejgonzalez left a comment

LGTM.

abejgonzalez merged commit f2ab3e3 into master

bkorpan deleted the bpd-tweaks-2 branch

February 6, 2020 17:24

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