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Exploring Design Space for 3D Clustered Architectures

Manu Awasthi, Rajeev BalasubramonianUniversity of Utah

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Device Layer 2Vertical Interconnect

Silicon

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• Multiple layers of active devices• Vertical interconnects between layers

Device Layer

Silicon

1

Courtesy: K.Bernstein, IBM

2D Chip

3D Chip

Layer 1

Layer 2

3D TechnologiesVerySmall

~ 10µm

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Benefits of 3D • Reduction of global interconnect

L

L

• Delay/Power reduction• Bandwidth• Mix-technology integration

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Previous Proposals

• Previously in 3D…– Break and stack (Folding) [Puttaswamy et

al]• Vertical stacking of active devices

RegFile

Break and Stack

All are active

HEAT!!!

Reduced Intra-block

latency

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An alternative approach?

2D Chip

3D Chip

Die 1

Die 0

Prudent Stacking Can:

• Improve Performance

• Result in better thermal profile

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Wire Delays and Performance

Impact of wire delays

0

5

10

15

20

25

30

35

40

45

50

0 2 4 6 8

Extra delay (in clock cycles)

Per

cent s

low

dow

n

DCACHE-INTALU

IQ-INTALU

RENAME-IQ

L1D-L2

BPRED-ICACHE

ICACHE-DECODE

DECODE-RENAME

DCACHE-FPALU

FPALU-INTALU

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Clustered Architectures

• Centralized front-end– I-Cache & D-Cache– LSQ, Rename, Decode– Branch Predictor

• Clustered back-end– Issue Queue– Regfile, FUs

L1 DCache

Cluster

Crossbar/Router

Front-End

Higher clock Frequency, High ILP!!

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Decentralized Cache Banks

L1 DCache

L1 DCache

L1 DCache

Possibly better performance

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Decentralized Cache Banks

L1 DCache

Replicated Cache Banks

L1 DCache

L1 DCache

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Decentralized Cache Banks

L1 DCache

Word Interleaved Cache Banks

L1 DCache

Odd Words Even Words

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Outline

• Introduction– Motivation– 3D Architectures– Clustered Architectures

• Proposals• Results • Conclusions

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Architecture 1

Cache-on-cluster

Die 1

Die 0

Cache Bank

Cluster

Inter Die Interconnect

Intra Die Interconnect

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Architecture 2

Cluster-on-cluster

Die 1

Die 0

Cache Bank

Cluster

Inter Die Interconnect

Intra Die Interconnect

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Architecture 3

Staggered

Die 1

Die 0

Cache Bank

Cluster

Inter Die Interconnect

Intra Die Interconnect

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Outline

• Introduction– Motivation– 3D Architectures– Clustered Architectures

• Proposals• Results • Conclusions

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Experimental Setup

• Framework– Simplescalar, Wattch and Hotspot 3.0– Wire model : 8x global metal plane

• Benchmarks– SPEC 2K, single threaded

• Processor Configuration– 8 Clusters– 64 kB L1 I/D Caches, 2 way set-assoc

• L1 Data cache Word-Interleaved or Replicated

• 2D Centralized Cache – Base Case

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Base Case PerformancesPerformance Improvement wrt 2D Centralized Cache

0.01.02.03.04.05.06.07.08.09.0

Replicated WI

Cache Bank Type

Per

form

ance

Impr

ovem

ent Best Case 2D Config

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The 3D EffectAverage Performance Improvement

0

2

4

6

8

10

12

14

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Arch 1 Arch 2 Arch 3

Perc

enta

ge Im

prov

emen

t ove

r 2D

Cent

raliz

ed

3D Replicated vs 2D Centralized

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The 3D EffectAverage performance Improvement

0

5

10

15

20

25

Arch 1 Arch 2 Arch 3Perc

enta

ge Im

pro

vem

ent over

Centr

alized

3D WI vs 2D Centralized

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Comparisons

Average Performance Improvement wrt 2D Centralized

0

5

10

15

20

25

Arch 1 Arch 2 Arch 3

IPC

Impr

ovem

ent

Average performance Improvement wrt 2D Centralized

0

5

10

15

20

25

Arch 1 Arch 2 Arch 3IP

C Im

prov

emen

t

3D Replicated 3D WI

Best Case 3D - Rep Best Case 3D - WI

12% Improvement for best case 3D vs best case 2D

Best Case 2D

2D Case

Base Case Performance Comparisons

0

5

10

15

20

25

Replicated WI

IPC

Impr

ovem

ent

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Thermal Analysis

• Wattch for power numbers• HotSpot 3.0 for thermal model (grid)

– 500x500 grid resolution

• Interconnect power modeling– Attributed to functional units– 8X plane wires– Router + Crossbar modeled as separate

entity

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Thermal Profiles

0

20

40

60

80

100

120

Base Arch 1 Arch 2 Arch 3

Pea

k Tem

p - H

ottes

t U

nit (C

)

Peak Temperature : Hottest on-chip Unit (Celsius)

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Outline

• Introduction– Motivation– 3D Architectures– Clustered Architectures

• Proposals• Results • Conclusions

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Conclusions

• Wire delays are critical to performance– Some are more important than others.

• Prudent block stacking– Performance improvement upto 12% over

2D• WI banks + Arch 3 (3D)

– Better thermal profiles compared to folding

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Backup Slides

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Cluster

(a) Arch-1 (cache-on-cluster) (b) Arch-2 (cluster on cluster) (c) Arch-3 (staggered)

Cache bank Intra-die horizontal wire Inter-die vertical wire

Die 1

Die 0

4 Cluster Arrangements