SchedUling on heterogeneous Mobile Multicores based on quality of ExpeRience

Users want mobile devices that appear fast and responsive, but at the same time have long lasting batteries and do not overheat. Achieving both of these at once is difficult. The workloads employed to evaluate mobile optimisations are rarely representative of real mobile applications and are oblivious to user perception, focussing only on performance. As a result hardware and software designers' decisions do not respect the user's Quality of Experience (QoE). The device either runs faster than necessary for optimal QoE, wasting energy, or the device runs too slowly, spoiling QoE. SUMMER will develop the first framework to record, replay, and analyse mobile workloads that represent and measure real user experience. Our work will expose for the first time the real Pareto trade-off between the user's QoE and energy consumption. The results of this project will permit others, from computer architects up to library developers, to make their design decisions with QoE as their optimisation target. To show the power of this new approach, we will design the first energy efficient operating system scheduler for heterogeneous mobile processors which takes QoE into account. With heterogeneous mobile processors just now entering the market, a scheduler able to use them optimally is urgently needed. We expect our scheduler to be at least 50% more energy efficient on average than the standard Linux scheduler on an ARM BIG.LITTLE system.

According to Gartner the global smartphone market is worth more than £400 billion annually in end user spending, with more than 1.3 billion smartphones sold every year. Battery life and performance are critical factors to end users, who want more powerful, smarter devices that last longer than a few hours. Providing tools to support and enable research towards a better trade-off between performance and energy consumption will have a wide economic and societal impact.

Outputs
We expect the impact of our work to come directly or indirectly from our project outputs. SUMMER will have these outputs:

1. Open source framework for mobile workload recording, replay, and analysis; 2. Open source prerecorded workloads;
3. Open source interaction lag prediction heuristics;
4. Open source heterogeneous scheduler based on user experience.

Impacts
The following is a list of the major impacts we want our work to achieve:

1. A change in the way optimisations are evaluated. We want design decisions, from compiler and operating systems heuristics, even down to choice of heterogeneity in multi-core processors, to be properly driven by quality of experience. We want for this to pervade multiple industries.
2. Standardised mobile benchmarks. We want the prerecorded workloads to become a standard benchmark suite, replacing the old suites that are not appropriate for performance-to- energy trade-offs.
3. Longer battery life or more powerful applications. Lowering the energy consumption of mobile devices will allow either more power hungry code to be used or for the devices to last longer between charges. This will be hugely beneficial for both the general public and business people. We expect this to come partly from our new scheduler, but also from derived works that use our new evaluation methodology or that embed the interaction lag predictors.