Implement the nice(1) command.

Write a set-user-ID-root program that is the realtime scheduling analog of nice(1). The command-line interface of this program should be as follows:

# ./rtsched policy priority command arg...

In the above command, policy is r for SCHED_RR or f for SCHED_FIFO. This program should drop its privileged ID before execing the command, for the reasons described in Section 9.7.1 and Section 38.3.

Write a program that places itself under the SCHED_FIFO scheduling policy and then creates a child process. Both processes should execute a function that causes the process to consume a maximum of 3 seconds of CPU time. (This can be done by using a loop in which the times() system call is repeatedly called to determine the amount of CPU time so far consumed.) After each quarter of a second of consumed CPU time, the function should print a message that displays the process ID and the amount of CPU time so far consumed. After each second of consumed CPU time, the function should call sched_yield() to yield the CPU to the other process. (Alternatively, the processes could raise each other’s scheduling priority using sched_setparam().) The program’s output should demonstrate that the two processes alternately execute for 1 second of CPU time. (Note carefully the advice given in Section 35.3.2 about preventing a runaway realtime process from hogging the CPU.)

If two processes use a pipe to exchange a large amount of data on a multiprocessor system, the communication should be faster if the processes run on the same CPU than if they run on different CPUs. The reason is that when the two processes run on the same CPU, the pipe data will be more quickly accessed because it can remain in that CPU’s cache. By contrast, when the processes run on separate CPUs, the benefits of the CPU cache are lost. If you have access to a multiprocessor system, write a program that uses sched_setaffinity() to demonstrate this effect, by forcing the processes either onto the same CPUs or onto different CPUs. (Chapter 44 describes the use of pipes.)