Parallel jobs running on same processors.

Hello,

I just got a KNL system which has 68 cores with 4 threads each. So basically, it should run 272 jobs. I submit my first job using mpiexec and used 64 of them. Then I submitted another one with 64. But when I checked the CPU usage, I found that the two jobs were running on the same 64 threads and left the rest empty. What kind of environmental variable should I set? Or what kind of job schedulers are recommended? Btw, we did not purchase the PBS because it is commercial and out our budget.

Thanks!