[julia-users] confusion with Julia -p 2

[Dan Y]

I use julia-0.4.5 on windows10 with pentium B970 (2 cores, 2 threads)

I have a code with no parallel instructions.
When I run it in a standard session with no options my CPU utilization is 
about 80-90%.
But when I run it in a session with "Julia -p 2" the CPU utilization is 
only about 20-25% .
And the code actually works about 3x times slower.

I wonder why. 
I didn't try to make code parallel yet, but I doubt it'll worth it.