Using a Virtual Machine Monitor to Slow Down CPU Speed for Embedded Time-Sensitive Software Testing

Abstract

The use of time-sensitive software has been popular for embedded systems like mobile phones and portable video players. Embedded software is usually developed in parallel with real hardware devices due to a tight time-to-market constraint, and therefore it is quite difficult to verify the sensory responsiveness of time-sensitive applications such as GUIs and multimedia players. To verify the responsiveness, it is useful for developers to observe the software's behavior in a test environment in which the software runs in real time rather than in simulation time. To provide such a test environment, we need a mechanism that slows down the CPU speed of test machines because test machines are usually equipped with high-end desktop CPUs. A CPU slowdown mechanism needs to provide various CPU speeds, keep a constant CPU speed in the short term, and be sensitive toward hardware interrupts. Although there are a couple of ways of slowing down CPU speed, they do not satisfy all the above requirements. This paper describes FoxyLargo that smoothly slows down CPU speed with a virtual machine monitor (VMM). FoxyLargo carefully schedules a virtual machine (VM) to provide an illusion that the VM is running slowly from the viewpoint of time-sensitive applications. For this purpose, FoxyLargo combines three techniques: 1) fine-grained, 2) interrupt-sensitive, and 3) clock-tick based VM scheduling. We applied our techniques to Xen VMM, and conducted three experiments. The experimental results show that FoxyLargo adequately meet all the above requirements. Also, we successfully reproduced the decoding behavior of an MPEG player. This result demonstrates that FoxyLargo can reproduce the behavior of real applications.