Origin: Kirkpatrick et al', "Optimization by Simulated Annealing", Science, 1983

1
Introduction

• Origin Kirkpatrick et al., "Optimization by
  Simulated Annealing", Science, 1983
• Idea
• Apply any combinatorial optimization problem
• TSP
• VLSI CAD

2
Algorithm
init
perturb
evaluate
decide
cool down
update
end?
result

• Generate a random configuration
• while stop_criterion(i, T) false
• for j ? 0 to N do
• new_config ? perturb(config)
• ?C ? eval(new_config, config)
• if ?C lt 0 or accept(?C, T)
• then config ? new_config
• T ? schedule(i, T)
• i ? i 1

3
In Actual Problem

• Settings
• Annealing schedule
• Acceptance rate
• Perturb method
• Inner loop times
• Evaluation method
• Tuning
• Important
• Differ from problem to problem
• Mostly empirical

4
Apply to Cell Placement

• Most well-developed method
• Very time consuming
• Though polynomial time but
• Much greater than O(nlogn)
• Excellent results

5
Implementations

• TimberWolf
• Developed by Carl Sechen and Sangiovanni-Vincentel
  li
• www.twolf.com/
• TimberWolf 7 ? iTools 1.4.0
• Alliance
• www-asim.lip6.fr/alliance/
• Ocean
• cas.et.tudelft.nl/software/ocean/
• Electric
• www.gnu.org/software/electric/electric.html

6
Parallelization

• Serial in nature?
• Almost
• Move acceleration
• Pipelining indeed
• Shared memory architecture only
• Limited parallelism
• Parallel moves
• Moves may interact to each other

7
Parallel Approaches

• Evaluate non-interacting moves in parallel
• Preserves the convergence
• Difficult to identity
• Evaluate all moves in parallel
• Maximum scope for parallelism
• Loss of quality
• Multiple Markov chains
• Near linear speed-up
• Local minimum trap
• Speculative computation
• Not feasible for cell placement

8
References

• 1 K. Shahookar and P. Mazumder, VLSI Cell
  Placement Techniques, ACM Computing Surveys,
  Volume 23, Issue 2, Pages 143-220, June 1991
• 2 J. A. Chandy and P. Banerjee, Parallel
  Simulated Annealing Strategies for VLSI Cell
  Placement, Proceedings of the 9th International
  Conference on VLSI Design VLSI in Mobile
  Communication, Page 37, 1996