10.3.5 RCU Exercises
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10.3.5 RCU Exercises

This section is organized as a series of Quick Quizzes that invite you to apply RCU to a number of examples earlier in this book. The answer to each Quick Quiz gives some hints, and also contains a pointer to a later section where the solution is explained at length. The rcu_read_lock(), rcu_read_unlock(), rcu_dereference(), rcu_assign_pointer(), and synchronize_rcu() primitives should suffice for most of these exercises.

Quick Quiz 10.61: The statistical-counter implementation shown in Figure (`count_end.c`) used a global lock to guard the summation in read_count(), which resulted in poor performance and negative scalability. How could you use RCU to provide read_count() with excellent performance and good scalability. (Keep in mind that read_count()'s scalability will necessarily be limited by its need to scan all threads' counters.) End Quick Quiz

Quick Quiz 10.62: Section showed a fanciful pair of code fragments that dealt with counting I/O accesses to removable devices. These code fragments suffered from high overhead on the fastpath (starting an I/O) due to the need to acquire a reader-writer lock. How would you use RCU to provide excellent performance and scalability? (Keep in mind that the performance of the common-case first code fragment that does I/O accesses is much more important than that of the device-removal code fragment.) End Quick Quiz