Recursive Bisection Placement*: feng shui 5.0

Ameya R. Agnihotri Satoshi Ono Patrick H. MaddenSUNY 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.

* We abandoned recursive bisection about 6 months ago…

Where is Kitakyushu?

feng shui versionshttp://vlsicad.cs.binghamton.edu

1.0: basic bisection engine [ISPD99,GLSVLSI01] iterative deletion, cycling, terminal propagation work.

1.5: cut sequence optimization [DAC01] paper with Rent’s rule.

2.0: Fractional cut [ICCAD03] results close to annealing; possible to place very very dense.

2.4, 2.6: Mixed size placement paper [ISPD04] results improved by 26% on average over the closest competing tool.

3.0: Structural (beacon) placer [ASPDAC05] new method designed to have fun with the PEKO benchmarks; currently within 22% of

optimal. 5.0: Integration of tools

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 CutMin cut (hMetis)

Area X

Area Y

Area Y

Area X

IBM01 before legalization

Placement Legalization

Standard cells: Dynamic programming approaches [ICCAD03], and

an unpublished method. Moving macro blocks:

[ISPD04] Extension of the tetris method by Hill. Fixed macro blocks:

Fractured row legalization [Khatkhate MS thesis].

ISPD04 Experimental ResultsCapo 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…

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 contestresult

The rightanswer

Example

How Much White Space Do You Really Need?

If you had 100X more space, would you really want to stretch that far?

Why do the industry guys do this? 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. We’ve integrated our global router and sizing tools

with the placer to avoid needing to insert excess space.

Placement Contest, Round 2

We’re going to lose round 1; that’s for sure. Apples vs. oranges problem; some of the apple placement methods are

going to look very bad… Who’s up for another round?

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)

Start with a “reference placement” 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 Keep the cell colors from the reference

Fun with the PEKOsIf 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 5.0Suboptimality Rogues Gallery

mPL Dragon Capo

Prof. Jason Cong

Prof. Majid Sarrafzadeh

Prof. Igor Markov

Prof. Patrick H. Madden

feng shui

Satoshi Ono

Beacon

26% HPWL improvement on mixed size, fractional cut, non-Manhattan, and what do people ask about?

The funny pictures from the GUI…