Transcript Improving Min-cut Placement for VLSI using Analytical

Benchmarking
for [Physical] Synthesis
Igor Markov and Prabhakar Kudva
The Univ. of Michigan / IBM
In This Talk …
Benchmarking vs benchmarks
 Benchmarking exposes new research Qs
 Why industry should care about
benchmarking
 What is (and is not) being done
to improve benchmarking infrastructure
 Not in this talk, but in a focus group
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Incentives for verifying published work
 How to accelerate a culture change
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Benchmarking
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Design benchmarks
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Objectives (QOR metrics) and constraints
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Algorithms, methodologies; Implementations
Solvers: ditto
Empirical and theoretical analyses, e.g.,
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Data model / representation; Instances
Hard vs easy benchmarks (regardless of size)
Correlation between different objectives
Upper / lower bounds for QOR, statistical behavior, etc
Dualism between benchmarks and solvers
For more details, see http://gigascale.org/bookshelf
Industrial Benchmarking
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Growing size & complexity of VLSI chips
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Design objectives
 Area
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/ power / yield / etc
Design constraints
 Timing
/ FP + fixed-die partitions / fixed IPs /
routability / pin access / signal integrity…
Can the same algo excel in all contexts?
 Sophistication of layout and logic motivate
open benchmarking for Synthesis and P&R
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Design Types
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ASICs
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SoCs
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Lots of fixed I/Os, few macros, millions of standard cells
Design densities : 40-80% (IBM)
Flat and hierarchical designs
Many more macro blocks, cores
Datapaths + control logic
Can have very low design densities : < 20%
Micro-Processor (P) Random Logic Macros(RLM)
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Hierarchical partitions are LS+P&R instances (5-30K)
High placement densities : 80%-98% (low whitespace)
Many fixed I/Os, relatively few standard cells
Note: “Partitioning w Terminals” DAC`99, ISPD `99, ASPDAC`00
Why Invest in Benchmarking
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Academia
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Industry
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Benchmarks can identify / capture
new research problems
Empirical validation of novel research
Open-source tools/BMs can be analyzed and tweaked
Evaluation and transfer of academic research
Support for executive decisions
(which tools are relatively week & must be improved)
Open-source tools/BMs can be analyzed and tweaked
When is an EDA problem (not) solved?
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Are there good solver implementations?
Can they “solve” existing benchmarks?
Participation / Leadership Necessary
Activity 1: Benchmarking platform / flows
 Activity 2: Establishing common evaluators
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Static timing analysis
 Congestion / yield prediction
 Power estimation
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Activity 3: Standard-cell libraries
 Activity 4: Large designs w bells & whistles
 Activity 5: Automation of benchmarking
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Activity 1: Benchmarking Platform
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Benchmarking “platform”: a reasonable subset of
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data model
specific data representations (e.g., file formats)
access mechanisms (e.g., APIs)
reference implementation (e.g., a design database)
design examples in compatible formats
Base platforms available (next slide)
More participation necessary
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regular discussions
additional tasks / features outlined
Common Methodology Platform
Synthesis
(SIS, MVSIS…)
Blif  Bookshelf format
Common Model
(Open Access?)
Placement
(Capo, Dragon,
Feng Shui, mPl,…)
Blue Flow exists, Common model hooks: To be Done
Placement Utilities
http://vlsicad.eecs.umich.edu/BK/PlaceUtils/
 Accept input in the GSRC Bookshelf format
 Format converters
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LEF/DEF  Bookshelf
Bookshelf  Kraftwerk (DAC98 BP, E&J)
BLIF(SIS)  Bookshelf
Evaluators, checkers,
postprocessors and plotters
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Contributions in these categories are welcome
Placement Utilities (cont’d)
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Wirelength Calculator (HPWL)
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Independent evaluation of placement results
Placement Plotter
Saves gnuplot scripts ( .eps, .gif, …)
 Multiple views (cells only, cells+nets, rows,…)
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Probabilistic Congestion Maps (Lou et al.)
Gnuplot scripts
 Matlab scripts
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 better
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graphics, including 3-d fly-by views
.xpm files ( .gif, .jpg, .eps, …)
Placement Utilities (cont’d)
Legality checker
 Simple legalizer
 Layout Generator
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Given a netlist, creates a row structure
 Tunable %whitespace, aspect ratio, etc
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All available in binaries/PERL at
http://vlsicad.eecs.umich.edu/BK/PlaceUtils/
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Most source codes are shipped w Capo
Activity 2: Creating Evaluators
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Contribute measures/analysis tools for:
Timing Analysis
 Congestion/Yield
 Power
 Area
 Noise….
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Benchmarking Needs for Timing Opt.
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A common, reusable STA methodology
High-quality, open-source infrastructure
 False paths; realistic gate/delay models
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Metrics validated against phys. synthesis
The simpler the better,
but must be good predictors
 Buffer insertion profoundly impacts layout
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 The
use of linear wirelength in timing-driven layout
assumes buffers insertion (min-cut vs quadratic)
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Apparently, synthesis is affected too
Vertical Benchmarks
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“Tool flow”
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Vertical benchmarks
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Two or more EDA tools, chained sequentially
(potentially, part of a complete design cycle)
Sample contexts: physical synthesis, place & route,
retiming followed by sequential verification
Multiple, redundant snapshots of a tool flow
sufficient info for detailed analysis of tool performance
Herman Schmit @CMU is maintaining
a resp. slot in the VLSI CAD Bookshelf
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See http://gigascale.org/bookself
Include flat gate-level netlists
Library information ( < 250nm)
Realistic timing & fixed-die constraints
Infrastructure Needs
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Need common evaluators of delay / power
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To avoid inconsistent / outdated results
Relevant initiatives from Si2
OLA (Open Library Architecture)
 OpenAccess
 For more info, see http://www.si2.org
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Still: no reliable public STA tool
 Sought: OA-based utilities for timing/layout
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Activity 3: Standard-cell Libraries
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Libraries carry technology information
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Some benchmarks in the Bookshelf
use 0.25m and 0.35m libraries
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Impact of wirelength delays
increases in recent technology generations
Cell characteristics must be compatible
Geometry info is there, + timing (in some cases)
Cadence test library?
Artisan libraries?
Use commercial tools to create libraries
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Prolific, Cadabra,…
Activity 4: Need New Benchmarks
To Confirm / Defeat Tool Tuning
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Data on tuning from the ISPD03 paper
“Benchmarking for Placement”, Adya et al.
Observe that
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Capo does well on Cadence-Capo, grid-like circuits
Dragon does well on IBM-Place (IBM-Dragon)
FengShui does well on MCNC benchmarks
mPL does well on PEKO
This is hardly a coincidence
Motivation for more / better benchmarks
P.S. Most differences above have been explained,
all placers above have been improved
Activity 4: Large Benchmark Creation
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www.opencores.org has large designs
May be a good starting point –
use vendor tools to create blif files
(+post results)
 Note: there may be different ways to convert
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A group of design houses
(IBM, Intel, LSI, HP)
is planning a release of new large
gate-level benchmarks for layout
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Probably no logic information
Activity 5: Benchmarking Automation
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Rigorous benchmarking is laborious. Risk of errors is high
How do we keep things simple / accessible?
Encapsulate software management in an ASP
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Web uploads for binaries and source in tar.gz w Makefiles
Web uploads for benchmarks
GUI interface for NxM simulations; tables created automatically
GUI interface for composing tool-flows; flows can be saved/reused
Distributed back-end includes job scheduling
Email notification of job completion
All files created are available on the Web (permissions & policies)
Anyone can re-run / study your experiment or interface with it
Follow-on Action Plan
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Looking for volunteers to -test Bookshelf.exe
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Create a joint benchmarking group
from industry and academia
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Particularly, in the context of synthesis & verification
Contact: Igor [email protected]
Contact: Prabhakar [email protected]
Regular discussions
Development based
on common infrastructure