[Simgrid-user] problems with SimDag

Arnaud Legrand Arnaud.Legrand at imag.fr
Thu Sep 13 17:03:35 CEST 2007


Today othmane nour wrote:

> I have two questions about SimDag:
>   - First question: I want to know if it is possible to stop a task on a
> machine M1 and to continue its execution on M2?

Err... no. And honnestly, implementing it in surf would require ...
erm! I don't know exactly what it would require but clearly a lots of
changes. However, it should be possible to kill a task and to start a
new one whose remaining computation is the same.

But let me ask just one question. Are you considering changing the
number of processors involved in the schedule of a task ?

>  - Second question: which are the tasks present on a machine at a given
> moment (because I want to compute the number of tasks present on each
> machine at a given moment t)?

For the moment, there is no way to access this info. It should not be
too hard to do. I would like to have more informations though and I'm
going to ask you the same questions as I asked Pablo a few days ago:

If there is a process engaged only in a communication, does it count
as a task ? What if all process running on this machine are suspended
(does that mean the machine is free of tasks) ?

> I have another question about MSG:
> MSG_process_change_host(process,host) is not implemented yet?

Arg, I should never have writen this prototype. I knew it would give
users bad ideas... ;) No, it's not implemented yet. Technically, it
should not be too difficult to do if you restrict it to
MSG_process_change_host(host) (i.e. if a process can only migrate
himself). Otherwise, it would get really tricky if a processor is
already engaged in a communication. What would you do then ? Reroute
the messages or something like that ? In short, I can easily write a
MSG_process_change_host function that only takes the targeted host as
an argument.



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