51'3 Compact Thermal Modeling for TemperatureAware Design

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Session 51
Wei Huang

• 51.3 Compact Thermal Modeling for
  Temperature-Aware Design

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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

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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.

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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

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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.

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Temperature-Aware Design Flow

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

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The Role of a Thermal Model

• Close the loop for accurate design estimations

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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.

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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.

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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

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Electrical-Thermal Duality

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

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Primary Heat Transfer Path

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

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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.

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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

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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.
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Result of Metal Layer Assignment
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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

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Power Grid Wire Lengths

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

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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.

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Equivalent Thermal Resistance of Wire

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

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Equivalent Thermal Resistance of Vias

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

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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.

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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.

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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.)

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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.

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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.

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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