GemDroid: a framework to evaluate mobile platforms

As the demand for feature-rich mobile systems such as smartphones and tablets has outpaced other computing systems and is expected to continue at a faster rate, it is projected that SoCs with tens of cores and hundreds of IPs (or accelerator) will be designed to provide unprecedented level of features and functionality in future. Design of such mobile systems with required QoS and power budgets along with other design constraints will be a daunting task for computer architects since any ad hoc, piece-meal solution is unlikely to result in an optimal design. This requires early exploration of the complete design space to understand the system-level design trade-offs. To the best of our knowledge, there is no such publicly available tool to conduct a holistic evaluation of mobile platforms consisting of cores, IPs and system software.

This paper presents GemDroid, a comprehensive simulation infrastructure to address these concerns. GemDroid has been designed by integrating the Android open-source emulator for facilitating execution of mobile applications, the GEM5 core simulator for analyzing the CPU and memory centric designs, and models for several IPs to collectively study their impact on system-level performance and power. Analyzing a spectrum of applications with GemDroid, we observed that the memory subsystem is a vital cog in the mobile platform because, it needs to handle both core and IP traffic, which have very different characteristics. Consequently, we present a heterogeneous memory controller (HMC) design, where we divide the memory physically into two address regions, where the first region with one memory controller (MC) handles core-specific application data and the second region with another MC handles all IP related data. The proposed modifications to the memory controller design results in an average 25% reduction in execution time for CPU bound applications, up to 11% reduction in frame drops, and on average 17% reduction in CPU busy time for on-screen (IP bound) applications.