In this article, we propose two techniques that aim to minimize the scheduling latency of high-priority interrupt-driven tasks, named the Interrupt Handler Migration (IHM) and Direct Interrupt Scheduling (DIS). The IHM allows the interrupt handler to be migrated from the interrupt handler thread to the corresponding target process so that additional context switch can be avoided and the cache hit ratio with respect to the data generated by the interrupt handler can be improved. In addition, the DIS allows the shortest path reserved for urgent interrupt-process pairs to be laid between the interrupt arrival and target process by dividing a series of interrupt-driven operations into nondeferrable and deferrable operations. Both the IHM and DIS can be combined in a natural way and can operate concurrently. These techniques can be applied to all kinds of interrupt handlers with no modification to them. The proposed techniques not only reduce the scheduling latency, but also resolve the interrupt-driven priority inversion problem. We implemented a prototype in the Linux 2.6.19 kernel after adding real-time patches. Experimental results show that the scheduling latency is significantly reduced by up to 84.2% when both techniques are applied together. When the Linux OS runs on an ARM-based embedded CPU running at 200MHz, the scheduling latency can become as low as 30 μ s, which is much closer to the hardware-specific limitations. By lowering the scheduling latency, the limited CPU cycles can be consumed more for user-level processes and less for system-level tasks, such as interrupt handling and scheduling.

In this paper, we propose a novel scheduling technique to improve the responsiveness of a real-time process while maintaining relative execution rates of non-real-time processes, called the prediction-based micro-scheduler. It runs upon an existing macro-scheduler and it conditionally rearranges the scheduling pattern generated by the macro-scheduler based on urgent interval prediction and lock hold time prediction. The rearrangement occurs if one process seeks to enter a long nonpreemptible section and the operation is predicted to significantly disturb the future execution of a real-time process. We implemented the prototype on Linux 2.6.19. Experimental results show that the average OS latency of a real-time process is reduced up to 34 percent of the original one while still maintaining relative execution rates of non-real-time processes. Moreover, the performance degradation caused by the micro-scheduler does not exceed 5 percent.

In this paper, we propose a new technique, called a delayed locking technique, to improve the real-time performance of embedded Linux. The proposed technique employs the rule that entering a critical section is allowed only if the operation does not disturb the future execution of the real-time application. To execute this rule, we introduce the concepts of timer interrupt prediction and lock hold time acquisition. In addition, we designed and implemented a new high-resolution timer that is simple, yet efficient. We implemented the prototype on Linux 2.4.18. Experimental results show that the worst-case OS latency of real-time process is reduced to 23% of the original one, at the expense of slowdown of the nonreal-time process by 20%. Though we focus only on embedded Linux, our technique is useful for all kinds of real-time operating systems in which the critical section is significantly long.