Insop Song, Ericsson

Predictability in real-time system is one the most important aspects; and a criterion for real-time operating systems is to provide a predictable scheduler to meet time constraints. In this research, a hardware/software hybrid design approach is presented to increase predictability of the operating system scheduler and reduce the overhead.

In most operating systems, a process scheduler runs most frequently and its critical task is to decide which process to schedule next, i.e. prioritizing processes. Except few simple operating systems, the selecting the next task requires non-trivial computation time, which varies depends on system loads or number of running processes. Therefore, the busiest software component in operating system is one of the sources of lowering predictability and increasing overhead. For example, Linux uses a priority queue called, Red-black tree, which sorts processes based on the scheduling key for the scheduler class used, to select the next process to run. Red-black tree is also used in high-resolution timer to sort based on expiration time.

In this research, a hardware priority queue, which is called tagged up/down sorter, is implemented and interfaced with operating system scheduler software. Implementing a priority queue with hardware guarantees the consistent computation time as well as shorter time then software implementation. A field programmable gate array (FPGA) is used for implementing HyOS (Hybrid Operating System) to holds a soft-core processor and a hardware priority queue. We implement HyOS with Linux as an operating system and MicroBlaze as a processor.

This approach demonstrates that HyOS approach both reduces computation time in finding next process with an order of magnitude and maintains consistent computation time unlike software counterpart.

In summary, we present an overview of previous hardware-assisted operating system research, and implement hybrid operating system with Linux, and then demonstrate the result. Further, we identify future research areas in hybrid operating system in single and multi-processor systems.