[Simgrid-user] General queries regarding Simgrid

Frédéric Suter frederic.suter at cc.in2p3.fr
Thu Jan 21 18:54:00 CET 2010


> I am a new user of Simgrid. I installed Simgrid and ran master/slave 
> application. I have some general queries regarding SImgrid MSG.
> 1) How to implement task dependency ? ( Example: If there are 3 tasks 
> t1, t2 and t3 . t2 can start only after t1 completes execution, t3 can 
> start only after t2 completes execution).
What you describe looks like a DAG. If this is correct, you may look at 
another SimGrid API called SimDAG. You can find some examples in 
> 2) How to share data between tasks ? ( Example: t2 should use t1 
> calculated data )
If this means a communication between t1 and t2, you have to create a 
third task (called C for instance). This task corresponds to the data 
transfer. Then you have to add dependencies between t1 and C and between 
C and t2.
> 3) Can I dynamically change the link properties like bandwidth, 
> latency, etc... ? If so, how ?
The way to do that is to use a trace file to your simulation run. This 
file describes the dynamic availability of the resources (either CPU and 
network). You can have a look at /examples/msg/trace to see how it works.
> 4) Can I have different tasks with different task size, communication 
> size and computation size ? If so, how ?
Of course. In the SimDAG API it's up to you to create the task with the 
cost you want.
> 5) Can I dynamically change the scheduling of tasks on hosts. I mean 
> whenever a host is free, i should execute a task on that host. If so, 
> how to ?
SimDAG was designed for the scheduling of DAG. Consequently you have a 
SD_task_schedule function that maps a task on a resource (computation 
task on CPU, communication task on a link/route)
> Please answer my queries 
I hope it is what I just did :)
> and please let me know where can I find a simple example of dynamic 
> scheduler.
SimGrid is not a simulator, just a toolbox giving you the building 
bricks to code your own simulator. So you will not find such example in 
the simgrid distribution.

Best regards,

F. Suter

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