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51'3 Compact Thermal Modeling for TemperatureAware Design

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Title: 51'3 Compact Thermal Modeling for TemperatureAware Design

1
Session 51
Wei Huang

51.3 Compact Thermal Modeling for
Temperature-Aware Design

Thank you for silencing all cell phones and
pagers and participating in the DAC Attendee
Survey at the end of the Session
2
Compact Thermal Modeling for Temperature-Aware
Design

Wei Huang, Mircea R. Stan, Kevin Skadron, Karthik
Sankaranarayanan, Shougata Ghosh, and Sivakumar
Velusamy
HPLP and LAVA labs, Departments of ECE and CS
University of Virginia
June 10, 2004
http//www.ece.virginia.edu/hplp
http//lava.cs.virginia.edu

3
Outline

Thermal challenges to the CAD community
Introducing temperature-aware design flow
Introducing a compact thermal model for
temperature-aware design flow
Primary heat transfer path
Secondary Heat transfer path
Wire-length estimation
Wire Self-heating current
Equivalent thermal resistance of wires and vias
Example applications of the compact thermal model
Conclusions.

4
Thermal Challenges to CAD

Overall and local power density ? ?Thermal effect
more important
Hot die and local hot spots on the die
Many design aspects are strongly thermal-related
Power, performance, reliability, etc.
Placement/routing, packaging, process, cost, etc.
Crucial to consider thermal effects

5
Outline

Thermal challenges to the CAD community
Introducing temperature-aware design flow
Introducing a compact thermal model for
temperature-aware design flow
Primary heat transfer path
Secondary Heat transfer path
Wire-length estimation
Wire Self-heating current
Equivalent thermal resistance of wires and vias
Example applications of the compact thermal model
Conclusions.

6
Temperature-Aware Design Flow

Temperature-aware design -- temperature as a
guideline throughout the entire design flow.
Intrinsically thermally optimized and free from
thermal limitations.

7
The Role of a Thermal Model

Close the loop for accurate design estimations

8
Requirements for a Thermal Model

Thermal model for temperature-aware design
should
Provide temperatures at different granularities.
Provide temperature for different parts of the
design.
Be computationally efficient.
Be reasonably accurate.
Previous work about thermal modeling.
At least one of the above requirements are not
satisfied.
So, need a new thermal model.

9
Outline

Thermal challenges to the CAD community
Introducing temperature-aware design flow
Introducing a compact thermal model for
temperature-aware design flow
Primary heat transfer path
Secondary Heat transfer path
Wire-length estimation
Wire Self-heating current
Equivalent thermal resistance of wires and vias
Example applications of the compact thermal model
Conclusions.

10
A Compact Thermal Model

We propose a compact thermal
Models all parts along both primary and secondary
heat transfer paths
At arbitrary granularities
Fast and accurate

11
Electrical-Thermal Duality

V ? temp (T)
I ? power (P)
R ? thermal resistance (Rth)
C ? thermal capacitance (Cth)
RC ? time constant

12
Primary Heat Transfer Path

Essentially a lumped thermal R-C network.
Done in our previous work at ISCA 30 HotSpot

13
Outline

Thermal challenges to the CAD community
Introducing temperature-aware design flow
Introducing a compact thermal model for
temperature-aware design flow
Primary heat transfer path
Secondary Heat transfer path
Wire-length estimation
Wire Self-heating current
Equivalent thermal resistance of wires and vias
Example applications of the compact thermal model
Conclusions.

14
Secondary Heat Transfer Path

Consists of on-die interconnect, C4 I/O pads,
ceramic/plastic substrate, BGA solder balls, and
printed circuit board.
Non-negligible heat dissipation (can be up to 30
of total heat).
On-chip interconnect thermal model
Useful to electromigration and IR drop analysis
Treat the self heating of signal and power supply
wires (VDDGND) separately
Self-heating power of a single wire
Average length of wires
Average wire self-heating current
Equivalent thermal resistance of the wires and
vias

15
Signal Interconnect Length Distribution

Using Rents Rule-based wire-length model by
Davis et al. to derive interconnect density
function of signal wires. (45nm, high-performance
microprocessor design, ITRS 2003)

J. A. Davis et al, Electron Devices, IEEE
Transactions on, 45(3)580589, March 1998.
16
Result of Metal Layer Assignment
17
Metal Layer Assignment of Signal Wires

A methodology of assigning signal wire of
different lengths to different metal layers.
The idea is to fill the area of each metal layer
with signal wires

18
Power Grid Wire Lengths

A power wire is a power grid section between
two nodes in the power distribution network.

19
Self-heating current of interconnects

For signal wires, the average self-heating
current can be estimated by solving
For power grid wires, current can be estimated by
simply dividing the total delivered current by
the number of power grid sections.

20
Equivalent Thermal Resistance of Wire

Wires are approximated by cylinders.
Left Single wire with inter-layer dielectric
Right -- Multiple wires with interlayer dielectric

21
Equivalent Thermal Resistance of Vias

Thermal resistance of each via.
Number of vias per signal wiring net.
Number of vias per power grid intersection.

22
Outline

Thermal challenges to the CAD community
Introducing temperature-aware design flow
Introducing a compact thermal model for
temperature-aware design flow
Primary heat transfer path
Secondary Heat transfer path
Wire-length estimation
Wire Self-heating current
Equivalent thermal resistance of wires and vias
Example applications of the compact thermal model
Conclusions.

23
An Example of Using the Thermal Model (1)

Parameters of a microprocessor design at 45nm
(based on ITRS roadmap), together with parameters
of its Level-one data cache as an example of
on-die local hot spots.

24
An Example of Using the Thermal Model (2)

More accurate compared to estimates based on room
temperature and worst-case temperature
Leakage power consumption, performance and life
time estimates across the die are shown in this
table. (Results are normalized to the estimates
based on our model.)

25
An Example of Using the Thermal Model (3)

Granularity is an important issue.
Local hot spot such as the L1 D-cache can be
significantly hotter than the other parts
Granularity within the L1 D-cache
Users are advised to choose proper granularities
suitable for their corresponding design stages.

26
Conclusions

Thermal effects has become one of the major
challenges to the CAD.
Operating temperature needs to be carefully
estimated and considered during the entire design
flow
Temperature-aware design is proposed as a
solution to the thermal challenges faced by the
designers.
A compact thermal model that meets the
requirement of temperature-aware design is
proposed. Modeling details are presented in this
talk as well as in the paper and an online
tech-report.
Application examples of the thermal model are
also presented.

27
More Information

For further information about this paper, the
following tech report is available online at
http//www.cs.virginia.edu/techrep/index.html
Compact thermal modeling for temperature-aware
design. Tech Report CS-2004-13, Univ. of Virginia
Dept. of Computer Science, April. 2004.
More information about temperature-related topics
about our research can be found at
http//www.ece.virginia.edu/hplp
http//lava.cs.virginia.edu