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Subject: Re: [OMPI users] using MPI through Qt
From: Eye RCS 51 (eye.rcs.51_at_[hidden])
Date: 2011-03-02 03:48:55

Hi David / users,

Thanks for your mail and suggestion.
Well, Can you please elaborate some more on this.

When I start program, without doing anything, nodes other than master keep
waiting for the corresponding MPI_Bcast call and keep taking nearly 50% CPU
while idle. When I MPI_Bcast the variable from master, then only other nodes
come to normal state. This is really a problem but it is unavoidable.

Also, is it possible for master to trigger a function/MPI call on all nodes
using any of MPI functionalities? This will be very useful.

Thank you very much for your feedback.

On Tue, Mar 1, 2011 at 8:05 AM, David Zhang <solarbikedz_at_[hidden]> wrote:
> Certainly you may call MPI functions many times, the problem is that you
> need to have matching receives (or collectives) at your slave nodes, which
> is only determined at run-time.  Perhaps this could be done with two
> communications, the first broadcast the type of communications to the slaves
> (for example, 1 for collective broadcast, 2 for scatter, etc.), you encode
> whatever you wish in an integer.  Once the slaves receive the code they'll
> respond correspondingly, posting the corresponding MPI receive.  Clearly, a
> way to allow the slaves to exit the while loop is needed if you want the
> slaves to exit cleanly, the exit code can also be encoded in the integer you
> sent out.
> On Tue, Mar 1, 2011 at 12:39 AM, Eye RCS 51 <eye.rcs.51_at_[hidden]> wrote:
>> Hi,
>> In an effort to make a Qt gui using MPI, I have the following:
>> 1. Gui started in master node.
>> 2. In Gui, through a pushbutton, a global variable x is assigned some
>> value; let say, x=1000;
>> 3. I want this value to be know to all nodes. So I used broadcast in the
>> function assigning it on the master node and all other nodes.
>> 4. I printed values of x, which prints all 1000 in all nodes.
>> 5. Now control has reached to MPI_Finalize in all nodes except master.
>> Now If I want to reassign value of x using pushbutton in master node and
>> again broadcast to and print in all nodes, can it be done??
>> I mean, can I have an MPI function which through GUI is called many times
>> and assigns and prints WHILE program is running.
>> OR simply can I have a print function which is printing noderank value in
>> all nodes whenever pushbutton is pressed while program is running.
>> command i used is "mpirun -np 3 ./a.out".
>> Any help will be appreciated.
>> Thanks you very much.
>> --
>> eye51
>> _______________________________________________
>> users mailing list
>> users_at_[hidden]
> --
> David Zhang
> University of California, San Diego
> _______________________________________________
> users mailing list
> users_at_[hidden]