Request Scheduling Algorithm Research For Web Server In Remote Control System

With the rapidly development of Internet and WWW, the web-basedremote control technology become a new orientation of development andhot research topic of the remote control field. Web server is the keycomponent for web-based remote control system, and decides whetherremote control system could accomplish a task quickly, accurately, andreliably. Furthermore, with the widely application of fiber and newgeneration switch in the Internet filed, the speed of network is more andmore quick. On the contrary, web server becomes the performancebottleneck of the web-based remote control system. The performance ofweb server relies on the performance of hardware and request schedulingalgorithm in web server software. In order to improve the performance ofweb server hardware, multi-core CPU is applied to web server. Theapplication of multi-core CPU to web server changes the runningenvironment of traditional web server software, and leads to new requestscheduling problems. So this paper proposed a new dynamic requestscheduling algorithm for multi-core web server, and studied the modelingof multi-core web server and ping-pong effect of multi-core web server. The research items are as follows:(1) Constructing the queueing network model for multi-core webserver. In order to analyze the performance of web server, there have beenmany performance models for web server based on queueing networktheory and Petri theory. But these performance models of web server arejust for the single-core web server. To evaluate the performance ofmulti-core web server, the thesis constructed the queueing network modelfor multi-core web server on the basis of the analysis of requestscheduling process and queueing network theory. The model uses Poissonprocess as input arrival process. At the same time, the model discusses theself-similar arrival process as well.(2) Studying the ping-pong effect of multi-core CPU. As it integratedmulti processing cores into one chip, multi-core CPU changed thestructure of caches too. There are usually multi-level caches in multi-coreCPU, which would lead to the problem of cache coherence. The problemof cache coherence is liable to cause the ping-pong effect betweenprocessor cores, which will greatly reduce the performance of multi-coreCPU. According to the research of threads scheduling policies of currentO/S and the cache structure of multi-core CPU, this thesis tried toeliminate the ping-pong effect by means of threads/processes hard affinitymethods provided by O/S. For validating the method, we do a simulationexperiment, and the experiment results proved that it is an effective method that eliminates the ping-pong effect by means of the affinity ofthreads/processes.(3) Proposing a dynamic request scheduling algorithm for multi-coreweb server. After making a thorough study in the process of handlingdynamic requests, in order to eliminate the ping-pong effect in multi-coreCPU, a new dynamic request scheduling algorithm is proposed accordingthe service time distribution of dynamic requests. The new algorithmclassifies the dynamic requests, and then the dynamic requests enter intothe different dynamic request queues. The threads that served for thesame dynamic request queue are assigned to the same processor core.Moreover, to keep the load balance between processor cores, the bestthreads assignment policy is calculated by means of Genetic Algorithm.(4) Conducting the simulation experiment based on the new dynamicrequest scheduling algorithm in multi-core web server. The simulationweb sever was developed on the basis of the new dynamic requestscheduling algorithm in multi-core web server. Furthermore, wedeveloped the sending module of Poisson arrival process and self-similararrival process. With the help of these tools, we conducted a series ofsimulation experiments. We measured the key indices of performance,such as response time distribution, mean response time, dropped rate andso on. At the same time, we do the simulation experiments based onshortest-job-first and first-come-first-served policies respectively, and compared their performance to the new dynamic request schedulingalgorithm.