Since the modified version of rcu-poll was unable to match the performance of rcu-ltimer, and since there are currently no known uses of RCU that require low grace-period latency, rcu-ltimer is used in the Linux 2.5 kernel. If needed, we will investigate use of rcu-poll's grace-period-latency mechanisms in rcu-ltimer after a fixed delay. A modified version of rcu-sched may attain even lower overheads than those of rcu-ltimer.
We will continue investigating how RCU may be used in the Linux kernel, including using it to provide NMI handler support and applying it to the tasklist_lock to eliminate some starvation scenarios that have been observed in the Linux 2.5 kernel. Experience gained from use of RCU in DYNIX/ptx, K42 [Gamsa99], and Linux indicate that it will continue to be quite helpful in obtaining dramatic performance improvements with little increase in complexity.