TECHNICAL REPORT 94-02 A Framework for Minimizing Thread Management Overhead Based on Asynchronous Cooperation between User and Kernel Schedulers

The performance of thread mechanism is dominated primarily by two kinds of thread-switching overheads: vertical switching (user/kernel domain switching) and horizontal switching (context switching between threads). Ideally, vertical switchings should occur only when system calls or external interrupts are invoked. Horizontal switchings within a user address space should occur only when threads synchronize with one another. Horizontal switchings in the kernel should occur only when processors are redistributed among user address spaces. Existing thread mechanisms, however, do not function ideally in a multiprogrammed system because (1) user-level programs determine how many threads to use, (2) the kernel does not inform the user level of which nor how many threads are actually being assigned processors, and/or (3) interaction between the kernel and user-level schedulers is synchronous. This paper presents a thread mechanism that minimizes the thread-switching overhead by avoiding these three problems; the kernel scheduler determines how many threads to use in each user address space, the kernel scheduler lets user-level schedulers know which threads are actually being assigned processors, and all interaction between the kernel scheduler and user-level schedulers is asynchronous. Employing these three ideas, the proposed mechanism minimizes thread switchings both in the kernel and in the user level, under the assumption that threads are managed without o -line information on applications to run. ANY OTHER IDENTIFYING INFORMATION OF THIS REPORT Submitted to IEEE Transactions on Parallel and Distributed Systems DISTRIBUTION STATEMENT First Issue 40 copies SUPPLEMENTARY NOTES REPORT DATE January 19, 1994 TOTAL NO. OF PAGES 24 WRITTEN LANGUAGE English NO. OF REFERENCES 22 DEPARTMENT OF INFORMATION SCIENCE Faculty of Science, University of Tokyo 7-3-1 Hongo, Bunkyo-ku Tokyo, 113 Japan A Framework for Minimizing Thread Management Overhead Based on Asynchronous Cooperation between User and Kernel Schedulers Shigekazu Inohara and Takashi Masuda