A CPU scheduler is found that a long$-$running CPU$-$bound job staying in low priority gets no chance to run when many short$-$running interactive jobs flood in$.$ Below which rule will cure this problem:

a$.$

After a preriod of time, move all jobs in the system to the upmost level priority.

b$.$

when a new job enters into the system, it is placed into the highest priority.

c$.$

After a job runs up its total allotment time given at a priority level, no matter how many times it gives up CPU, demote it to the next priority level.

d$.$

When a job runs up its time slice, move it to the next lower$-$level priority.