[mpich-discuss] resources are equally shared when running processes in one machine ?

[Gra zeus]

hello,
when i run my mpi code with "mpiexec -n 1 ./myprogram", everything work fine.
however, when i rn with "mpiexec -n 4 ./myprogram", performance of my program dropped significantly. 
I code my program to work only for "process 0" like this:-     if(id=0){  do_computation_task(); } else {  //do_nothing };
Is this mean physical resources are shared when I spawn more than one process in one physical machine(even all of work were done by "process 0" and other processes do nothing)?
If the answer is "yes", can you pls tell me if it's stated somewhere in official document that I can make reference to. 
Thx,Gra




      
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