scheduler help

[alexis]

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.