I have done some research on the net regarding the problem. My questions is NOT how to reduce cpu utilization by improving algorithm or improving the performance by using multitasking or limiting CPU per system user.

I have a website where user logs in does some processing and logout. The site uses linux server, php and apache. The problem is that I cant control the amount of CPU allocated to each user. ie I want give a guarantee that a user will get say atleast 5% of CPU (assume total number of users is less than 20). How can I do this?

Any solution (A php code, apache server settings, or any out of box soln) is welcomed.

Thankyou very much for reading this :)