Recursive Bisection
Placement*: feng shui 5.0
* We abandoned recursive bisection about 6 months ago…
Ameya R. Agnihotri Satoshi Ono Patrick H. Madden
SUNY Binghamton CSD, FAIS, University of Kitakyushu
(with code by Mehmet Can Yildiz and Ateen Khatkhate, and with help from
Purdue’s Cheng-Kok Koh and Chen Li)
This work was supported by an IBM Faculty Partnership Award, SRC Project
947.1, an equipment grant from Intel, NYSTAR MDC, and by funds from the
Japanese Ministry of ECSST via Kitakyushu and Fukuoka knowledge-based
cluster project.
Where is Kitakyushu?
feng shui versions
http://vlsicad.cs.binghamton.edu
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1.0: basic bisection engine
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1.5: cut sequence optimization
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[ISPD04] results improved by 26% on average over the closest
competing tool.
3.0: Structural (beacon) placer
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[ICCAD03] results close to annealing; possible to place very very dense.
2.4, 2.6: Mixed size placement paper
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[DAC01] paper with Rent’s rule.
2.0: Fractional cut
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[ISPD99,GLSVLSI01] iterative deletion, cycling, terminal propagation work.
[ASPDAC05] new method designed to have fun with the PEKO benchmarks; currently within
22% of optimal.
5.0: Integration of tools
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GUI front end, [GLSVSLI00] non-Manhattan global router, [DAC03] global router, [ISCAS05]
delay analysis, PowerARC delay library, support for LEF/DEF, gate sizing tool… Versions of
the stand-alone placer are available in both hMetis and MLPart flavors.
5% or so improvements on mixed size placement (with minor tuning).
The bisection based placement engine is now in maintainence mode; we’ll fix minor
problems, but it’s not our main focus.
Bisection Based Placement
Logic elements
Semiconductor chip
Fractional Cut Bisection
Mixed Size Fractional Cut
Area Y
Min cut
(hMetis)
Area Y
Area X
Area X
IBM01 before legalization
Placement Legalization
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Standard cells:
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Moving macro blocks:
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Dynamic programming approaches [ICCAD03], and
an unpublished method.
[ISPD04] Extension of the tetris method by Hill.
Fixed macro blocks:

Fractured row legalization [Khatkhate MS thesis].
ISPD04 Experimental Results
Capo 1
ISPD02
Capo 2
ICCAD03
Capo 3
ICCAD03
mPG-ms
ASPDAC03
Feng Shui 2.4
ISPD04
Ibm01
3.96
3.36
3.05
3.01
2.41
Ibm02
8.37
8.23
6.83
7.42
5.34
Ibm03
12.16
11.53
10.38
11.20
7.51
Ibm04
13.48
11.93
10.11
10.50
7.96
Ibm05
11.51
11.20
11.10
10.90
10.10
Ibm06
10.25
9.63
9.94
9.21
6.82
Ibm07
15.75
15.80
15.25
13.70
11.71
…
Average
1.29
1.26
1
As much as 51% better on some benchmarks. Closest
is around 8%, for the design that doesn’t have macro
blocks.
Now about the contest…
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The designs have very large amounts of internal
white space (apples vs. oranges)
Space MUST be distributed internally to have
any chance of a good result (due to fixed
locations of the macro blocks)
We have no support at all for internal white
space distribution

Or, to be more precise… The correct location for
white space is usually outside of the core.
Example
IBM
Our contest
result
The right
answer
Example
How Much White Space Do You
Really Need?
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If you had 100X more space, would you
really want to stretch that far?
Why do the industry guys do this?
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Put space in early for sizing and routability
Or even better, use something like….
[ICCAD04] cut line shifting for routability.
 [ASPDAC05], same idea for gate sizing and buffer
insertion.
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We’ve integrated our global router and sizing
tools with the placer to avoid needing to insert
excess space.
Placement Contest, Round 2
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We’re going to lose round 1; that’s for sure.
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Who’s up for another round?
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Apples vs. oranges problem; some of the apple placement
methods are going to look very bad…
Moving macro blocks?
Rotation of blocks?
Mirroring cells?
Or round 1 again, but give me some time to finish the move
away from recursive bisection!
Routing benchmark announcement

Patrick Groeneveld, Jurjen Westra, and myself, have been
working on global routing benchmarking. We’ll talk about this at
EDP. WANTED: more research groups in routing!
Better Visualization (feng shui 5.0
GUI version)
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Start with a “reference placement”
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For the PEKOs, this is the known optimal
Map pixel colors from an image onto cells
in the reference placement
Rearrange the cells to match a placement
under study
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Keep the cell colors from the reference
Fun with the PEKOs
If the placement is optimal, the mapped image should be
identical to the reference image.
Source Image
(Prof. Jason
Cong)
Optimal placement for PEKO01
in the feng shui 5.0 GUI
Image mapped onto the cells
And then rearranged to match
the placement of mPL
feng shui 5.0
Suboptimality Rogues Gallery
mPL
Prof. Jason Cong
Prof. Majid Sarrafzadeh
Prof. Igor Markov
Prof. Patrick H. Madden
Satoshi Ono
Dragon
Capo
feng shui Beacon
26% HPWL
improvement on
mixed size,
fractional cut,
non-Manhattan,
and what do
people ask
about?
The funny
pictures from the
GUI…