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27B elementRayleigh-Taylor Instability(MIRANDA, BG/L)

VisIt: a visualization tool for large turbulence simulations

Large data requires special techniques. This image was made by using a distributed

memory parallel program that partitioned the data over the processors, performing I/O,

processing, and rendering in parallel.

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VisIt calculated connected components on a 4K^3 turbulence data in parallel using TACC's Longhorn machine. 2 million components were initially identified and then the map expression was used to select only the components that had total volume greater than 15. Data courtesy of P.K. Yeung & and Diego Donzis

Visualizing and Analyzing Large-Scale Turbulent Flow

Detect, track, classify, and visualize features in large-scale turbulent flow.

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Flow analysis for 217 pin simulation / 1 billion grid points

217 pin reactorcooling simulation.Run on ¼ of Argonne BG/P.

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Flow analysis for 217 pin simulation / 1 billion grid points

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Tracing particles through the channels

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Tracing particles through the channels

Place 1000 particles in one channel

Observe which channels the particles come out

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This analysis depended on improvements in parallel particle advection

Two extremes:• Partition data over processors

and pass particles amongst processors Parallel inefficiency!

• Partition seed points over processors and process necessary data for advection Redundant I/O!

Notional streamlineexample

Notional streamlineexample

P0 P0 P0 P0 P0

P1 P1 P1 P1 P1

P2 P2 P2 P2 P2

P3 P3 P3 P3 P3

P4 P4 P4 P4 P4

P0

P1

P2

P3

P4

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Hybrid solution:• Master-slave approach that

adapts between parallel inefficiencies and redundant I/O

P0P0

P1

P1

P2

P2P3

P4

Iteration Action

0 P0 reads B0,P3 reads B1

1 P1 passes points to P0,P4 passes points to P3,P2 reads B0

0: Read

0: Read

Notional streamlineexample

Notional streamlineexample

1: Pass

1: Pass

1: Read

- Decision of when to pass or read is simplified here and based on load of

processors owning data. - Heuristic weights against I/O, but allows

for redundant I/O- All coordination done by slave masters.

This analysis depended on improvements in parallel particle advection

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VisIt is a richly featured, turnkey application

• VisIt is an open source, end user visualization and analysis tool for simulated and experimental data

– Used by: physicists, engineers, code developers, vis experts

– >100K downloads on web

• R&D 100 award in 2005• Used “heavily to exclusively” on 8

of world’s top 12 supercomputers

217 pin reactor coolingsimulation. Run on ¼ of Argonne BG/P.

1 billion grid points

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Terribly Named!! Intended for more than just visualization!

Data Exploration

VisualDebugging Quantitative Analysis

Presentations

=?

Comparative Analysis

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VisIt has a rich feature set that can impact many science areas.

Meshes: rectilinear, curvilinear, unstructured, point, AMR Data: scalar, vector, tensor, material, species Dimension: 1D, 2D, 3D, time varying Rendering (~15): pseudocolor, volume rendering,

hedgehogs, glyphs, mesh lines, etc… Data manipulation (~40): slicing, contouring, clipping,

thresholding, restrict to box, reflect, project, revolve, … File formats (~85) Derived quantities: >100 interoperable building blocks

+,-,*,/, gradient, mesh quality, if-then-else, and, or, not Many general features: position lights, make movie, etc Queries (~50): ways to pull out quantitative information,

debugging, comparative analysis

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VisIt employs a parallelized client-server architecture.

Client-server observations:• Good for remote

visualization• Leverages available

resources• Scales well• No need to move data

Additional design considerations:• Plugins• Multiple UIs: GUI (Qt), CLI

(Python), more…

remote machine

Parallel vis resources

Userdata

localhost – Linux, Windows, Mac

Graphics Hardware

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The VisIt team focuses on making a robust, usable product for end users.

Manuals• 300 page user manual• 200 page command line interface manual• “Getting your data into VisIt” manual

Wiki for users (and developers) Revision control, nightly regression testing, etc Executables for all major platforms Day long class, complete with exercises

Slides from the VisIt class

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VisIt is a vibrant project with many participants.

Over 50 person-years of effort Over one million lines of code Partnership between: Department of Energy’s Office of Nuclear

Energy, Office of Science, and National Nuclear Security Agency, and among others

2004-6

User communitygrows, includingAWE & ASC Alliance schools

Fall ‘06

VACET is funded

Spring ‘08

AWE enters repo

2003

LLNL user communitytransitioned to VisIt

2005

2005 R&D100

2007

SciDAC Outreach Center enablesPublic SW repo

2007

Saudi Aramcofunds LLNL to support VisIt

Spring ‘07

GNEP funds LLNL to support GNEP codes at Argonne

Summer‘07

Developers from LLNL, LBL, & ORNLStart dev in repo

‘07-’08

UC Davis & UUtah research done in VisIt repo

2000

Project started

‘07-’08

Partnership withCEA is developed

2008

Institutional supportleverages effort from many labs

Spring ‘09

More developersEntering repo allthe time

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● Weak scaling study: ~62.5M cells/core

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#coresProblem Size

ModelMachine

8K0.5TIBM P5Purple

16K1TSunRanger

16K1TX86_64Juno

32K2TCray XT5JaguarPF

64K4TBG/PDawn

16K, 32K1T, 2TCray XT4Franklin

VisIt was recently demonstrated to show good performance at unprecedented scales.

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Three Ways To Get Data Into VisIt

(1) Write to a known output format (2) Write a plugin file format reader (3) Integrate VisIt “in situ”

• “lib-VisIt” is linked into simulation code (Note: Memory footprint issues with

implementation!)• Use model:

simulation code advances at some time interval (e.g. end of cycle), hands

control to lib-VisIt. lib-VisIt performs vis & analysis tasks, then hands

control back to simulation code repeat 16

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VisIt: What’s the Big Deal?

What’s the big deal?• Everything works at scale• Robust, usable tool• Vis to code development to scientific insight

Learn more:• Google: “visit visualization”• http://www.llnl.gov/visit / http://www.visitusers.org• visitusers@ornl.gov

Live & online tutorials• Publicly available SVN• Hank Childs,

hchilds@lbl.gov17