thanks for your explain here. iam trying wrote into file which have 4.5 MB and 115 MB. i think that large amount data. iam using file JPG and MP4 extension. actually this program about Advanced Encryption Standard (AES), iam gonna try to using MPI I/O for reducing execute time this program. oh what do you mean about "that only recovers at much higher levels of parallelism"? can you explain the details and with example? thanks a lot for your attention

1) when i trying execute my program using MPI-I/O. why when iam execute with 1 proses, execute time more good than when iam execute with 2 proses. am i wrong? this is my source code.

In general, with one process doing i/o the file system can cache the heck out of requests. When a second process comes along, the caching needs to be disabled or invalidated, causing a "performance crash" that only recovers at much higher levels of parallelism. Let's look specifically at your code, though: MPI_File_open (MPI_COMM_WORLD, file_akhir, MPI_MODE_CREATE | MPI_MODE_WRONLY, MPI_INFO_NULL, &hasil); int jumlah1 = (((block-1)*16)+pad); int jumlah = jumlah1 / size; MPI_File_set_view(hasil, rank * jumlah * sizeof(char), MPI_CHAR, MPI_CHAR, "native", MPI_INFO_NULL); MPI_File_write (hasil, output, jumlah1, MPI_CHAR, MPI_STATUS_IGNORE); MPI_File_close(&hasil); - Are you writing a large amount of data or a small amount of data here? - What file system are you using? -- Rob Latham Mathematics and Computer Science Division Argonne National Lab, IL USA ------------------------------ _______________________________________________ discuss mailing list [email protected] https://lists.mpich.org/mailman/listinfo/discuss