My apologies, I think I wasn't clear on my question. My question was, given that copying of data is necessary in both approaches (either by the system with arrays or by programmer with buffers), is there a foreseeable performance difference in terms of performance considering the time it takes for copying?
Thank you, Saliya On Fri, Aug 22, 2014 at 3:24 PM, Oscar Vega-Gisbert <ov...@dsic.upv.es> wrote: > El 22/08/14 20:44, Saliya Ekanayake escribió: > > Thank you Oscar for the detailed information, but I'm still wondering how >> would the copying in 2 would be different than what's done here with >> copying to a buffer. >> > > If you have a buffer array like this: > > double buffer[] = new double[m * n]; > > Copy the 2D matrix to the buffer: > > > for(int i = 0; i < m; i++) > System.arraycopy(matrix[i], 0, buffer, i * n, n); > > Copy from the buffer to the 2D matrix: > > > for(int i = 0; i < m; i++) > System.arraycopy(buffer, i * n, matrix[i], 0, n); > > >> On Fri, Aug 22, 2014 at 2:17 PM, Oscar Vega-Gisbert <ov...@dsic.upv.es >> <mailto:ov...@dsic.upv.es>> wrote: >> >> El 22/08/14 17:10, Saliya Ekanayake escribió: >> >> Hi, >> >> I've a quick question about the usage of Java binding. >> >> Say there's a 2 dimensional double array (size m x n) that >> needs to be sent to another rank. I see two options to get >> this done, >> >> 1. Copy values to a direct buffer of size m*n and send it >> 2. Copy values to a 1D array of size m*n and send it >> >> I guess 2 would internally do the copying to a buffer and use >> it, so suggesting 1. is the best option. Is this the case or >> is there a better way to do this? >> >> >> The best option is 1 because 2 requires one extra copy to C heap. >> Supposing the matrix is the following: >> >> double matrix[][] = new double[m][n]; >> >> Then you can allocate a direct DoubleBuffer: >> >> DoubleBuffer buffer = MPI.newDoubleBuffer(m * n); >> >> In order to send/receive the matrix I suggest to use the bulk >> put/get methods: >> >> for(int i = 0; i < m; i++) >> buffer.put(matrix[i]); // Copy to the buffer. >> >> MPI.COMM_WORLD.send(buffer, m*n, MPI.DOUBLE, 1, 0); >> >> The receive code: >> >> MPI.COMM_WORLD.recv(buffer, m*n, MPI.DOUBLE, 0, 0); >> >> for(int i = 0; i < m; i++) >> buffer.get(matrix[i]); // Copy from the buffer. >> >> Note that bulk get/put methods increment the buffer position in n. >> So if you want reuse the buffer you must set the buffer position >> to 0 before copy the matrix: >> >> buffer.position(0); >> >> Regards, >> Oscar >> >> >> Thank you, >> Saliya >> -- Saliya Ekanayake esal...@gmail.com <mailto: >> esal...@gmail.com> >> <mailto:esal...@gmail.com <mailto:esal...@gmail.com>> >> >> http://saliya.org >> >> >> _______________________________________________ >> users mailing list >> us...@open-mpi.org <mailto:us...@open-mpi.org> >> >> Subscription: http://www.open-mpi.org/mailman/listinfo.cgi/users >> Link to this post: >> http://www.open-mpi.org/community/lists/users/2014/08/25130.php >> >> >> _______________________________________________ >> users mailing list >> us...@open-mpi.org <mailto:us...@open-mpi.org> >> >> Subscription: http://www.open-mpi.org/mailman/listinfo.cgi/users >> Link to this post: >> http://www.open-mpi.org/community/lists/users/2014/08/25131.php >> >> >> >> >> -- >> Saliya Ekanayake esal...@gmail.com <mailto:esal...@gmail.com> >> >> Cell 812-391-4914 Home 812-961-6383 >> http://saliya.org >> >> >> _______________________________________________ >> users mailing list >> us...@open-mpi.org >> Subscription: http://www.open-mpi.org/mailman/listinfo.cgi/users >> Link to this post: http://www.open-mpi.org/community/lists/users/2014/08/ >> 25132.php >> > > _______________________________________________ > users mailing list > us...@open-mpi.org > Subscription: http://www.open-mpi.org/mailman/listinfo.cgi/users > Link to this post: http://www.open-mpi.org/community/lists/users/2014/08/ > 25133.php > -- Saliya Ekanayake esal...@gmail.com Cell 812-391-4914 Home 812-961-6383 http://saliya.org
