1. CS533 - Concepts of Operating Systems 1 CS533 Concepts of Operating Systems Class 8 Synchronization on Multiprocessors

2. CS533 - Concepts of Operating Systems 2 Questions  What is the problem with trying to acquire a lock in interrupt handling code?  How can we prevent race conditions on variables that are used by interrupt handlers? o Is this the same as cooperative multitasking?  What if a variable is accessed in normal kernel context and in an interrupt handler?  How should we manage data accessed during deferred interrupt processing (soft-irqs)?

3. CS533 - Concepts of Operating Systems 3 Questions  Why spin-wait instead of blocking? o What is the downside of spin-waiting?  Why is it bad to perform an operation that might block in a critical section protected by a spin lock?

4. Questions  How does a reader writer lock improve performance compared to a normal lock? o Is it necessarily a win?  How does the Linux Big Reader Lock improve read performance compared to a normal reader-writer lock? CS533 - Concepts of Operating Systems 4

5. 5 Questions  Why is it difficult to implement a spin lock that exhibits good performance? o Why does a simple spin on test and set approach perform poorly? o Why doesn’t a spin on read approach help much? o Why isn’t it very helpful to have a solution that works well only for long critical sections?  Why might you want to distinguish and prioritize the “clear” requests over the “test and set” requests?

6. CS533 - Concepts of Operating Systems 6 Questions  How can a waiting process notice that a lock has been released?  If it polls how can we avoid having all waiting processes … o poll at the same time? o poll at the same place?

7. Questions  In what ways does transactional memory support more concurrency than locking?  Why is high contention a problem for transactional memory?  Why is I/O a problem for transactional memory?  What is the solution to these problems? CS533 - Concepts of Operating Systems 7