Michel Dierks wrote: > Geoff Jacobs wrote: >> Michel Dierks wrote: >> >>> Hello, >>> >>> I'm developing an application to calculate the Mandelbrot fractal. >>> >> Hmm... I never did this when I was learning the ropes. There is a pretty >> example included with the mpich source code to do Mandelbrot fractals if >> you need something to crib from. >> >> >>> My problem is: >>> >>> from the master I will send to each free node for computation a message >>> containing the values of one screen line. >>> >> I would think you can get away with transmitting just the boundaries of >> the section of complex plane which you will be plotting, as well as the >> iterative limit, color interpretation, etc. Slaves can determine what >> portion they must calculate from their ranks. >> >> >>> After a time the nodes will send back the results. >>> >>> I have see that I can use MPI_Isend and MPI_Irecv for non-blocking >>> communication. This give me no problem if we are talking about of one >>> send and one receive. But how can I handle the sending from each node to >>> the master without data corruption. >>> Must I implement a send and a receive buffer for each node (16 nodes >>> means 16 buffer in and 16 out) ? >>> >> The software I've implemented has tended to be rather dynamic, so it >> seemed easier to use discrete sends and receives. In your case, you will >> be calculating a vector of fixed size on each slave (one row for your >> resultant image per). It would be logical to use a collective >> communicator like MPI_Gather to automatically populate the array >> representing your raster image. >> http://csit1cwe.fsu.edu/extra_link/pe/d3a64mst07.html#HDRIGATH >> >> >>> Can someone help me? Please >>> _______________________________________________ >>> Beowulf mailing list, Beowulf@beowulf.org >>> To change your subscription (digest mode or unsubscribe) visit >>> http://www.beowulf.org/mailman/listinfo/beowulf >>> >>> >> >> Hello, >> it is now 2 days that I'm facing with the following problem. >> The master send messages to nodes (about 200 separate messages for >> each node). >> I cannot group them, I must send messages after messages to each >> nodes and to response to Geoff Jacobs I cannot use MPI_Gather because >> I must determined on which node I will send the next message ( based >> on list of free nodes). >> My send is running correctly and my receive too for the first message >> but not for the second. I can see that the master send the second >> message and that MPI_Iprobe on the node see that a message is arrived. >> But after this MPI_Iprobe , MPI_IRecv doesn't work this time. Why ?? I >> have made some research on the mpi forum and on some other places but I >> cannot found a correct explanation. All example given are more talking >> about one send and one receive but not on multiple send and receive on >> more than one node. I have found the routine MPI_Request_free and test >> it but this one give error telling me that I have an invalid handler. >> After some research again, I have found this at >> http://www.pdc.kth.se/training/Talks/MPI/Persistent/more.html Point 2 >> on the page: >> >> "When a program calls a non-blocking message-passing routine such as >> |MPI_Isend|, a request object is created, and then the >> communication is started. These steps are equivalent to two other MPI >> calls, |MPI_Send_init| and |MPI_Start|. When >> the program calls |MPI_Wait|, it waits until all necessary >> local operations have completed, and then frees the memory used to >> store the request object. This second step equals a call to >> |MPI_Request_free|." >> >>> So I don't understand anymore what to do. >>> Can someone of you tell me clearly what I'm doing wrong? Here below >>> the part of my code who run on the nodes: >>> /***************************** >>> * Parts running on node * >>> *****************************/ /* Memory >>> Allocation to buffer_sendi and buffer_recvd */ if >>> ((buffer_sendi=(int *)malloc(MAX_INT * sizeof(int)))==NULL) >>> { >>> exit(1); >>> } >>> if ((buffer_recvd=(double *)malloc(MAX_DOUBLE * >>> sizeof(double)))==NULL) >>> { >>> exit(1); >>> } >>> /* Until receive tag with value -99 loop */ >>> do { >>> MPI_Iprobe(0,MPI_ANY_TAG,MPI_COMM_WORLD,&flag,&status_recvd); >>> if (flag==1) >>> { >>> /* Reception from master */ >>> >>> MPI_IRecv(buffer_recvd,MAX_DOUBLE,MPI_DOUBLE,0,tag,MPI_COMM_WORLD,&status_recvd); MPI_IRecv(buffer_recvd,MAX_DOUBLE,MPI_DOUBLE,0,status_recvd.MPI_TAG,MPI_COMM_WORLD,&request);
>>> MPI_Wait(&request_recvd,&status); MPI_ISend and MPI_IRecv both take a request argument, and both do not take a status argument. The arguments for async comms are different than for sync. http://www.mpi-forum.org/docs/mpi-11-html/node46.html Tag, in the case of the MPI_IRecv should be status_recvd.MPI_TAG, not tag. >> /* >> some calculation >> */ >> /* send buffer_sendi to master */ >> >> MPI_ISend(buffer_sendi,MAX_INT,MPI_INT,0,tag,MPI_COMM_WORLD); Here, tag can be anything. You do need a request variable, as noted above. >> MPI_Wait(&request_recvd,&status); >> } >> }while(buffer_recvd[0]!=-99.00); >> Thanks for your help. >> -- Geoffrey D. Jacobs Go to the Chinese Restaurant, Order the Special _______________________________________________ Beowulf mailing list, Beowulf@beowulf.org To change your subscription (digest mode or unsubscribe) visit http://www.beowulf.org/mailman/listinfo/beowulf
