Integrated Scheduling for Reducing the Delays by Priority Inversion in Real-Time Web Service

Sukyong JUNG  Bongjik KANG  Kyunghee CHOI  Kihyun CHUNG  

IEICE TRANSACTIONS on Communications   Vol.E86-B    No.7    pp.2143-2153
Publication Date: 2003/07/01
Online ISSN: 
Print ISSN: 0916-8516
Type of Manuscript: PAPER
Category: Internet
WWW,  Web service,  real-time,  priority inversion,  scheduling,  

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This paper proposes a real-time scheduling mechanism for web server that finds a way to solve so-called priority inversion problem between tasks handling real-time web requests with higher priorities and tasks with lower priorities like HTML requests. The priority inversion problem of web server stems from operating two independent schedulers, web scheduler and kernel scheduler, without exchanging scheduling information or considering the requirement of each other. In the proposed mechanism, two schedulers are integrated in a kernel and the integrated scheduler schedules real-time web tasks and other application tasks together based on their priorities. Since the unified scheduler sees all tasks simultaneously in system, it can schedule the tasks with their absolute priorities and reduce the execution delay caused by the priority inversion. The proposed mechanism provides web server with a better chance to efficiently serve real-time web requests. The feasibility and performance of the proposed mechanism are empirically shown on an embedded system.