Asterisk CPU CORES USAGE

Hello everyone,
My problem is the following:
I have a server with 8 cores (4 physical cores)
I have an Asterisk 1.4
I did isolcpus 0,1 in grub to disable 2 cores on restart
i want to separate asterisk from other process
Then I made taskset 0-1 pid of asterisk
so far everything is good
my problem is that Asterisk only uses the first core, the second is still 0%
would there a solution to this problem
Thank you for your answers
sorry for my bad english