scheduler help

hello to everyone , l have a assignment and i need help. i have to change the scheduler function at kernel 2.6.38 so that the scheduler choose the process with the least slack time. My problem : i have create a function that iterates all runnable processes finds the one with least slack time(lst) and returns a pointer to the task( struct task_struct*) Now i need to change the scheduler so that selected for execution the process with lst. i am trying to change the function pick_next_task_fair in file sched_fair.c but i cant understand the code in there can someone explain me ? is the pick_next_task_fair the right function that need change? if yes it is the only one ? sorry for my English thanks.