Kernel Korner - AEM: a Scalable and Native Event Mechanism for Linux

We performed testing to measure the behavior of AEM during a simple exchange between two remote processes. This test was done to ensure the time needed to context switch an event handler did not cause a performance problem. More recently, we also performed benchmarking to measure the scalability of AEM and to test the internal implementation of jobs and wait queues, which represent the base functionality of AEM.

Figure 6. AEMhttpd, a single-threaded HTTP server used to make scalability measurements of the AEM internal implementation. Here we have performed 100 active connections for each sample.

In order to generate figures we could compare easily, we decided to use an existing Web server and adapt it with the AEM interface. AEMhttpd is a simple single-threaded HTTP server (see Resources.) A single-threaded server runs entirely in the main thread of execution. It means that neither kernel threads nor user threads are created to handle HTTP requests. The measurements done with this type of server focus on the implementation capabilities rather than on the performance of the server itself.

In the example illustrated in Figure 6, we have run 100 active transactions. For each transaction, we increased the number of open connections to increase the number of jobs in the sockets' connection wait queues. In a standard server implementation based on select(), this would have increased the time to respond to requests, because all descriptors would have been scanned in sequence. With AEM, only active jobs (that is, sockets with data ready) execute their corresponding event handlers. This proves that AEM provides a generic and scalable implementation.

Linux is widely used in the industry, imposing itself as the operating system of choice for enterprise-level solutions. It also is on the edge of becoming the operating system of choice for the next-generation IP-based architectures for telecom services. There already is a wide acceptance of Linux capabilities, but providing enhancements at the kernel level will attract the next-generation service providers that demand scalability, performance and reliability.

AEM is a solid attempt to provide the asynchronous notification of processes together with event data completion. It also brings an event-driven methodology that enables a secure programming paradigm for application developments. In addition, AEM implements a mechanism that focuses on increasing application reliability and portability by exporting a simple user interface.

All of the researchers at the Open Systems Lab and Lars Hennert at Ericsson for their useful comments, and Ericsson Research for approving the publication of this article.

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