topic Re: Differentiating Broadcast and Recv messages in Intel® Moderncode for Parallel Architectures

Differentiating Broadcast and Recv messages

Jimmy821 — Tue, 06 Jan 2009 18:23:36 GMT

Hi,

My code performs broadcasting and transmission using bcast and isend simultaneously.

At the receiving end, how can I differentiate between bcast and isend messages? The program is multi-threaded with a receiving end for broadcast messages and received messages. I discover that if I incorrectly accepts an incoming data with ibcast function, the program would crash. How can I best resolved this?

Thanks for helping.

Kind Regards,
Jimmy

Re: Differentiating Broadcast and Recv messages

Henry_G_Intel — Fri, 09 Jan 2009 23:55:16 GMT

Hi Jimmy,

MPI_Bcast is a collective operation. There's no mechanism for it to accept messages from apoint-to-point function like MPI_Isend.Are youdoing something like this?

[cpp]switch(rank) { 
    case 0: 
        MPI_Bcast(buf1, count, type, 0, comm); 
        MPI_Send(buf2, count, type, 1, tag, comm); 
        break; 
    case 1: 
        MPI_Recv(buf2, count, type, 0, tag, comm, status); 
        MPI_Bcast(buf1, count, type, 0, comm); 
        break; 
}[/cpp]

This code is incorrect because the MPI processes reverse theorder of point-to-point and collective communication. The MPI Forum shows several examples of erroneous collective operations: http://www.mpi-forum.org/docs/mpi-11-html/node86.html#Node86. Can you post some pseudocode illustrating what your program is doing?

Best regards,
Henry

Re: Differentiating Broadcast and Recv messages

Jimmy821 — Sun, 11 Jan 2009 16:59:56 GMT

Quoting - Henry Gabb (Intel)

Hi Jimmy,

MPI_Bcast is a collective operation. There's no mechanism for it to accept messages from apoint-to-point function like MPI_Isend.Are youdoing something like this?

[cpp]switch(rank) { 
    case 0: 
        MPI_Bcast(buf1, count, type, 0, comm); 
        MPI_Send(buf2, count, type, 1, tag, comm); 
        break; 
    case 1: 
        MPI_Recv(buf2, count, type, 0, tag, comm, status); 
        MPI_Bcast(buf1, count, type, 0, comm); 
        break; 
}[/cpp]

I wanted to distribute out data as a broadcast to all the slave threads.

However, I require the slave threads to return different types of objects back to the master which perform the broadcast. A simple bcast operation is not sufficient because it does not different the types.

In addition, I may want to perform inter-process communications in between the slave threads. I feel riding on top of MPI infrusturture is the best.

Thanks.