Question

In Chapter 5, we discussed possible race conditions on various kernel data structures. Most scheduling algorithms maintain a run queue, whichlistsprocesseseligibletorunonaprocessor.Onmulticoresystems, there are two general options: (1) each processing core has its own run queue, or (2) a single run queue is shared by all processing cores. What are the advantagesand disadvantages of each of these approaches?

Answer 1

• The main advantage of every processing core having its own run queue is that there is no contention over a solo run queue when the scheduler is running simultaneously on two or more processors.
• When a scheduling decision should be made for a processing core, the scheduler only want to look no further than its private run queue.
• A disadvantage of a particular single run queue is that it have to be protected with locks to avoid a race condition and a processing core may be accessible to run a thread, yet it must first acquire the lock to regain the thread from the single queue.
• Though, load balancing would expected not be an issue with a single run queue, while when each processing core has its own run queue, there should be some sort of load balancing between the dissimilar run queues.