Cactus in GrADS HFA

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Cactus in GrADS (HFA)

• Ian Foster
• Dave Angulo, Matei Ripeanu, Michael Russell

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Presentation Outline

• Introduction to Cactus
• Cactus Applications
• Cactus Architecture
• Cactus Worm Thorn
• Tequila Thorn (Cactus in GrADs)
• Tequila Architectur
• Issues

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What is Cactus?

• Cactus is a freely available, modular, portable
  and manageable environment for collaboratively
  developing parallel, high-performance
  multidimensional simulations

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Example Cactus Output
Example output from Numerical Relativity
Simulations
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Cactus Applications

• Application Thorns are Astrophysics applications
• Calculate Schwartzchild Event Horizons for
  colliding black holes

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Cactus Applications (cont.)

• Candidate apps are Elliptical Solver or BenchADM
• Abstract Topologies are simple 3D Grid

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Cactus Applications (cont.)

• Applications can easily be linked in with the
  other thorns used as tools.
• Application Thorns are just selected and run with
  the other selected thorns

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Cactus Architecture
Cactus
Thorns
Computational Toolkit
Toolkit
Toolkit
Flesh
Make
Configure
CST
Operating Systems
SuperUX
Irix
Linux
Unicos
HP-UX
Solaris
OSF
NT
AIX
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Cactus Model (cont.)
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Running Cactus
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Cactus model

• This is the currently working Cactus application
  framework that we will modify

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Worm Thorn Functions

• Initiates moving to new resource when scheduled
  time is exhausted
• Contacts IS to get a new node to run on
• Checkpoints application
• Restarts application on the new node
• Runs on single node only

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GrADS Cactus Model

• We will start with Worm thorn code to make new
  Tequila thorn (Apotheosized Cactus Worm).

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Tequila thorn functions

• Receives event (generated by user) to initiate
  adapting resources.
• Contacts ResourceSelector to get new bag of
  resources
• Checkpoints application
• Restarts application on the new resources

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Events

• Events that cause the user to want to adapt
  resources
• User changes parameters during runtime that
  requires additional resources
• Example starting an analysis routine
• Example running an event horizon finder
• User specifies that performance is not meeting
  expectations

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Future Events

• Possible Future Plans for automatic resource
  adapting
• User changes parameters during runtime that
  requires additional resources
• Contract violations fire similar events
• we were wrong first time
• resources get overloaded
• more (or fewer) (or different) processors appear
• distribution changed
• resolution changed

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Tequila thorn contacts ResourceSelector

• ResourceSelector must be set up as service
• Tequila thorn sends request for new bag of
  resources
• ResourceSelector responds with the new bag

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Request and Response

• The Request to the ResourceSelector will be
  stored in the InformationService
• Only the pointer to the data in the IS will be
  passed to the ResourceSelector
• The Response from the ResourceSelector will also
  be stored in the IS
• Only the pointer to the data in the IS will be
  passed back.

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Tequila communication overview
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Cactus Architecture in GrADS
Cactus
Thorns
Computational Toolkit
Toolkit
Flesh
Make
Configure
CST
Operating Systems
SuperUX
Irix
Linux
Unicos
HP-UX
Solaris
OSF
NT
AIX
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Open Issues

• How does Contract Monitor fit into architecture?
• How does PPS fit into architecture?
• How does COP and Aplication Launcher fit into
  architecture (Cactus has its own launcher and
  compiles its own code)?
• How does Pablo fit into architecture (Which
  thorns are monitored, is flesh monitored)?

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End of Presentation
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Communication Details step 1

• Event sent to Tequila thorn requesting restart

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Communication Details step 2

• Tequila store AART in IS

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Communication Details step 3

• Tequila sends request to ResourceSelector passing
  pointer to data in IS

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Communication Details step 4

• ResourceSelector retrieves AART from IS

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Communication Details step 5

• ResourceSelector stores bag of resources (in
  AART) in IS

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Communication Details step 6

• ResourceSelector responds to Tequila passing
  pointer to data in IS

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Communication Details step 7

• Tequila retrieves AART with new bag of resources
  from IS

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Requirements

• Using the IS for communication adds overhead.
• Why do this?
• GrADS requirement 1 do some things (e.g.
  compile) at one time and have the results stored
  in a persistent storage area. Pick these stored
  results up later and complete other phases.

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Requirements (cont.)

• GrADS requirement 2 Application people want to
  be able to allow users to manually interact in
  any of the "module interfaces." Tequila allows
  this to be done with a web client.

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Parallelism in Cactus

• Cactus is designed around a distributed memory
  model. Each thorn is passed a section of the
  global grid.
• The actual parallel driver (implemented in a
  thorn) can use whatever method it likes to
  decompose the grid across processors and exchange
  ghost zone information - each thorn is presented
  with a standard interface, independent of the
  driver.

• Standard driver distributed with Cactus (PUGH) is
  for a parallel unigrid and uses MPI for the
  communication layer
• PUGH can do custom processor decomposition and
  static load balancing

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Sample Tequila Scenario

• User asks to run an ADM simulation 400x400x400
  for 1000 timesteps in 10s.
• Resource selector contacted to obtain virtual
  machines
• Best virtual machine selected based on
  performance model.
• AM starts Cactus on that virtual machine (and
  monitors execution Contracts?)
• User (or application manager) decides that
  computation advances too slow and decides to
  search for a better virtual machine
• AM finds a better machine, commands the Cactus
  run to Checkpoint, transfers files and restart
  Cactus