Memory interference characterization and mitigation for heterogeneous smartphones

The availability of a wide range of general purpose as well as accelerator cores on

modern smartphones means that a significant number of applications can be executed

on a smartphone simultaneously, resulting in an ever increasing demand on the memory

subsystem. While the increased computation capability is intended for improving

user experience, memory requests from each concurrent application exhibit unique

memory access patterns as well as specific timing constraints. If not considered, this

could lead to significant memory contention and result in lowered user experience.

This work first analyzes the impact of memory degradation caused by the interference

at the memory system for a broad range of commonly-used smartphone applications.

The real system characterization results show that smartphone applications,

such as web browsing and media playback, suffer significant performance degradation.

This is caused by shared resource contention at the application processor’s last-level

cache, the communication fabric, and the main memory.

Based on the detailed characterization results, rest of this thesis focuses on the

design of an effective memory interference mitigation technique. Since web browsing,

being one of the most commonly-used smartphone applications and represents many

html-based smartphone applications, my thesis focuses on meeting the performance

requirement of a web browser on a smartphone in the presence of background processes

and co-scheduled applications. My thesis proposes a light-weight user space frequency

governor to mitigate the degradation caused by interfering applications, by predicting

the performance and power consumption of web browsing. The governor selects an

optimal energy-efficient frequency setting periodically by using the statically-trained

performance and power models with dynamically-varying architecture and system

conditions, such as the memory access intensity of background processes and/or coscheduled applications, and temperature of cores. The governor has been extensively evaluated on a Nexus 5 smartphone over a diverse range of mobile workloads. By

operating at the most energy-efficient frequency setting in the presence of interference,

energy efficiency is improved by as much as 35% and with an average of 18% compared

to the existing interactive governor, while maintaining the satisfactory performance

of web page loading under 3 seconds.