Is Parallel Programming Hard, And, If So, What Can You Do About It?

8.3. READ-COPY UPDATE (RCU) 107also contains a pointer to a later section where thesolution 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 8.61: The statistical-counter implementationshown in Figure 4.8 (count_end.c)used a global lock to guard the summation in read_count(), which resulted in poor performance andnegative scalability. How could you use RCU toprovide read_count() with excellent performanceand good scalability. (Keep in mind that read_count()’s scalability will necessarily be limited byits need to scan all threads’ counters.)Quick Quiz 8.62: Section 4.5 showed a fancifulpair of code fragments that dealt with counting I/Oaccessestoremovabledevices. Thesecodefragmentssufferedfromhighoverheadonthefastpath(startingan I/O) due to the need to acquire a reader-writerlock. How would you use RCU to provide excellentperformanceandscalability? (Keepinmindthattheperformance of the common-case first code fragmentthat does I/O accesses is much more important thanthat of the device-removal code fragment.)