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Some Limits of Power Delivery in the Multicore Era

Runjie Zhang, Brett H. Meyer, Wei Huang, Kevin Skadron and Mircea R. Stan

University of Virginia, McGill University,

IBM Austin Research Lab.

ITRS Projection on Transistor Density (2011 Edition)

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2011 2012 2013 2014 2015 2016 2017 2018 2019 2020 2021 2022 2023 2024 2025 20260

10000

20000

30000

40000

50000

60000

70000

80000

Year

Mtr

an

sist

ors

/cm

2

Source: ITRS 2011

Power Density and Current Density

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45nm 32nm 22nm 16nm0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

Power Density Current Density

Tech Node

W/m

m2

A/m

m2

Current = Power / Supply Voltage

The Chip - Package

4 Source: pcgameshardware.com

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The Chip – Inside the Package

Source: ITRS 2009Edition,

The Chip – C4 Bumps

Source: flipchips.com,Source: Wikipedia

What are the problems?

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2011

2013

2015

2017

2019

2021

2023

2025

2500

3000

3500

Year

Tota

l Pa

d C

ount

Source: ITRS 2011Edition,

3.7% 5.6% 7.4% 11.1%0%

50%

100%

150%

200%

250%

300%

IR drop

Maxim

um

Dela

y I

ncre

ase

Source: Shao et al. IEEE Computer Society Annual Symposium on VLSI, 2005

Source: Ye et al. Applied Physics letters, 2003

Electromigration

Architecture Level PDN Model

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• Input:– PDN physical parameters. E.g. metal width– Processor floorplan and powermap.– Pad configuration

• Output:– Voltage pad– Pad current

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Architecture Level PDN Model

Validation

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• IBM Power Grid analysis benchmarks– Steady-State– SPICE format– Provides details about metal layer and Pad

locations

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Power Map

VDD Pad Distribution

IBM_PG6

Validation Results

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Pad Current Comparison

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Multicore Scaling

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Baseline: 3.7GHz, Duo Core, Intel Penryn 4-way OoO Processor

Private L2 cache, 3MB per core

Mesh-Based NoC

  45nm 32nm 22nm 16nm# of Cores 2 4 8 16Area(mm2) 116.4 124.8 131.5 149.3

Supply Voltage 1 0.9 0.8 0.7Peak Total Power (W) 74.62 100.5 116.8 148.5

Peak Total Current(A) 74.6 111.6 145.9 212.1

Flooplan

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Power Delivery Noise Scaling Trend

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Pad Optimization

17

18

Sorted Pad Current After Optimization

Sorted Pad Current Before Optimization

I/O vs. Power Supply

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Const core-to-MC ratio

80 pads per MC

5% IR drop target

Thermal vs. Power Delivery

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Conclusions

• Power delivery is becoming a limiting factor in near future;

• IR drop poses a bigger challenge than ElectroMigration;

• Memory bandwidth will be affected’• With liquid cooling, scaling hit power

delivery wall before thermal wall.

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Questions?

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Thanks!

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Temerature Map vs. Voltage Map

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Voltage (V) Temperature(o C)

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Volta

ge (V

)Te

mpera

ture

(oC

)