hi guys,

According to my understanding, linux default scheduling policy is SCHED_OTHER. I just like to know how do we modify the scheduling so that it will exhibit the same behavior as the POSIX4 SCHED_FIFO scheduling policy.

I have spent too much time investigated on this area already but dont know where to start as you all know the size of sched.c is more than 1000 lines of code.

Please would you please give me a good direction on how to start? and which part of the code should i concentrate on? modify kernel require some careful thought before begin coding because it there is a bug the kernel can boot up

You really don't need to be in the kernel...
man sched_setscheduler
Will let you set a process' scheduling policy.

Do you know any way to remove the default scheduler in linux? and implement a new scheduler ( SCHED_FIFO) so that it can support real time application?

Ingo Molnar has been working on real time performance
The fruits of his labors are here

http://people.redhat.com/mingo/realtime-preempt/