int main(int argc, char *argv[]) {
if (argc < 4) {
printf("Usage: %s threads n repetitions\nWhere n make sense in range [25; 45]\n",argv[0]);
return 1;
}
int P = atoi(argv[1]);
volatile long n = atol(argv[2]);
int T = atoi(argv[3]);
// warmup parallel engine
ParallelFib(n);
dump_title();
// collect serial time
long serial_result = 0;
tbb::tick_count t0;
for (int t = -1; t < T; ++t) {
if (t == 0) t0 = tbb::tick_count::now();
serial_result += SerialFib(n);
}
double serial_elapsed = (tbb::tick_count::now() - t0).seconds();
output(0,n,0,T,serial_elapsed,serial_elapsed,serial_result);
// perform search
find_cutoff(P,n,T,serial_elapsed);
return 0;
}
void find_cutoff(const int P, const long n, const int T, const double serial_elapsed) {
long lo = 1, hi = n;
double elapsed = 0, lo_elapsed = 0, hi_elapsed = 0;
long final_cutoff = -1;
tbb::task_scheduler_init init(P);
while(true) {
CutOff = calculate_new_cutoff(lo, hi);
long result = 0;
tbb::tick_count t0;
for (int t = -1; t < T; ++t) {
if (t == 0) t0 = tbb::tick_count::now();
result += ParallelFib(n);
}
elapsed = (tbb::tick_count::now() - t0).seconds();
output(P,n,CutOff,T,serial_elapsed,elapsed,result);
if (serial_elapsed / elapsed >= P/2.0) {
final_cutoff = CutOff;
if (hi == CutOff) {
if (hi == lo) {
// we have had this value at both above and below 50%
lo = 1; lo_elapsed = 0;
} else {
break;
}
}
hi = CutOff;
hi_elapsed = elapsed;
} else {
if (lo == CutOff) break;
lo = CutOff;
lo_elapsed = elapsed;
}
}
double interpolated_cutoff = lo + ( P/2.0 - serial_elapsed/lo_elapsed ) * ( (hi - lo) / ( serial_elapsed/hi_elapsed - serial_elapsed/lo_elapsed ));
if (final_cutoff != -1) {
printf("50%% efficiency cutoff is %ld ( linearly interpolated cutoff is %g )\n", final_cutoff, interpolated_cutoff);
} else {
printf("Cannot achieve 50%% efficiency\n");
}
return;
}
