"Unstable Threads" Kernel Interface for Minimizing the Overhead of Thread Switching

The performance of threads is limited primarily by the overhead of two kinds of switching: vertical switching (user/kernel domain switching) and horizontal switching (context switching between threads). Although these switchings are indispensable in some situations, existing thread mechanisms involve unnecessary switchings on multiprogrammed systems, because of inappropriate interfaces between the operating system kernel and user-level programs. This paper presents a set of interfaces between the kernel and user-level programs that minimizes the overhead of the two kinds of switchings. The kernel provides ‘unstable threads,’ which are controlled solely by the kernel, while each user-level program monitors them and gives suggestions on their activities to the kernel through a shared memory area between the kernel and user address spaces. This new way of separating thread management minimizes the overhead of vertical and horizontal switchings.