Task/ChannelMessage-passing TaskProcess Explicit channelsMessage communication.

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Presentation transcript:

Task/ChannelMessage-passing TaskProcess Explicit channelsMessage communication

Not satisfied 0

Embarrassingly parallel: No channels between tasks

#include

int main (int argc, char *argv[]) { int i; int id; /* Process rank */ int p; /* Number of processes */ void check_circuit (int, int); Include argc and argv : they are needed to initialize MPI One copy of every variable for each process running this program

MPI_Init (&argc, &argv);

MPI_COMM_WORLD Communicator Processes Ranks Communicator Name

MPI_Comm_size (MPI_COMM_WORLD, &p);

MPI_Comm_rank (MPI_COMM_WORLD, &id);

0 id 6 p 4 6 p 2 6 p 1 6 p 5 6 p 3 6 p

int total; int main (int argc, char *argv[]) { int i; int id; int p; … Where is variable total stored?

for (i = id; i < 65536; i += p) check_circuit (id, i); Parallelism is outside function check_circuit It can be an ordinary, sequential function

MPI_Finalize();

#include #include int main (int argc, char *argv[]) { int i; int id; int p; void check_circuit (int, int); MPI_Init (&argc, &argv); MPI_Comm_rank (MPI_COMM_WORLD, &id); MPI_Comm_size (MPI_COMM_WORLD, &p); for (i = id; i < 65536; i += p) check_circuit (id, i); printf ("Process %d is done\n", id); fflush (stdout); MPI_Finalize(); return 0; } Put fflush() after every printf()

/* Return 1 if 'i'th bit of 'n' is 1; 0 otherwise */ #define EXTRACT_BIT(n,i) ((n&(1<<i))?1:0) void check_circuit (int id, int z) { int v[16]; /* Each element is a bit of z */ int i; for (i = 0; i < 16; i++) v[i] = EXTRACT_BIT(z,i); if ((v[0] || v[1]) && (!v[1] || !v[3]) && (v[2] || v[3]) && (!v[3] || !v[4]) && (v[4] || !v[5]) && (v[5] || !v[6]) && (v[5] || v[6]) && (v[6] || !v[15]) && (v[7] || !v[8]) && (!v[7] || !v[13]) && (v[8] || v[9]) && (v[8] || !v[9]) && (!v[9] || !v[10]) && (v[9] || v[11]) && (v[10] || v[11]) && (v[12] || v[13]) && (v[13] || !v[14]) && (v[14] || v[15])) { printf ("%d) %d%d%d%d%d%d%d%d%d%d%d%d%d%d%d%d\n", id, v[0],v[1],v[2],v[3],v[4],v[5],v[6],v[7],v[8],v[9], v[10],v[11],v[12],v[13],v[14],v[15]); fflush (stdout); }

mpicc –O -o foo foo.c

% mpirun -np 1 sat 0) ) ) ) ) ) ) ) ) Process 0 is done

% mpirun -np 2 sat 0) ) ) ) ) ) ) ) ) Process 0 is done Process 1 is done

% mpirun -np 3 sat 0) ) ) ) ) ) ) ) ) Process 1 is done Process 2 is done Process 0 is done

int MPI_Reduce ( void *operand, /* addr of 1st reduction element - this is an array */ void *result, /* addr of 1st reduction result - element-wise reduction of array (*operand)..(*operand+count-1) */ int count, /* reductions to perform */ MPI_Datatype type, /* type of elements */ MPI_Op operator, /* reduction operator */ int root, /* process getting result(s) */ MPI_Comm comm /* communicator */ )

MPI_Reduce (&count, &global_count, 1, MPI_INT, MPI_SUM, 0, MPI_COMM_WORLD); Only process 0 will get the result if (!id) printf ("There are %d different solutions\n", global_count);

% mpirun -np 3 seq2 0) ) ) ) ) ) ) ) ) Process 1 is done Process 2 is done Process 0 is done There are 9 different solutions

double elapsed_time; … MPI_Init (&argc, &argv); MPI_Barrier (MPI_COMM_WORLD); elapsed_time = - MPI_Wtime(); … MPI_Reduce (…); elapsed_time += MPI_Wtime(); /* better, remove barrier, and take the max of individual processes’ execution times */

ProcessorsTime (sec)