1. Progress Report 2012/12/12

2. Computation Offloading Mobile devices have limited energy and computing resources. Offloading some workloads to remote servers leads to: ◦ Power-saving. ◦ Performance improving.  Shorter execution time.  Better results.

3. Computation Offloading(Cont.) Offloading granularity: ◦ Process level  Process migration. ◦ Function/Method level Target ◦ Android apps. ◦ Activity + Service

4. Applicable Image processing ◦ object recognition, OCR, face detection, barcode analysis Audio processing ◦ speech recognition Text processing ◦ machine translation Artificial intelligence for games ◦ Chess 3D rendering ◦ 3D home interior design Security ◦ taint analysis and virus scans

5. Related Works Cyber foraging ◦ a pervasive computing technique where resource poor, mobile devices offload some of their heavy work to stronger surrogate machines in the vicinity. ◦ Several studies since ‘01. Scavenger(‘09) CloneCloud(‘10) MAUI(’10)

6. Related Works(Cont.) Most of the existing works focus more on power than performance. ◦ The most important element is the network speed, then the computation ability of server. Recent studies focus on “how to make offloading decisions”. ◦ Formulate into a 0-1 ILP problem.

7. Our Idea Instead of studying offloading policies, we aim at the effects caused by offloading. After offloading, a computation-intensive process becomes I/O-intensive. ◦ Does this phenomenon affects scheduler? ◦ Does this phenomenon affects DVFS? ◦ Does this phenomenon affects cache/memory? ◦ …etc.

8. Our Idea(Cont.) Identify the influence of property change. ◦ Computation-intensive => I/O-intensive. Understand Android's strategies for thread scheduling, thread allocation, thread migration, DVFS, and DPM.

9. Thread Scheduler Completely Fair Scheduler(CFS) ◦ Since Linux 2.6.23 ◦ /kernel/sched.c ◦ Maintain balance (fairness) in providing processor time to tasks.  Red-Black Tree Brain Fuck Scheduler(BFS) ◦ (pseudo)deadline for each task. ◦ Suitable for less than 16 cores.

10. Cuckoo A framework that helps developers to offload computation to the server. Offloading decisions are made by Cuckoo framework. ◦ Offload if the remote resource is reachable.

11. Problem Service thread ◦ Computation-intensive => I/O-intensive ◦ Task in waiting state will not be scheduled.

12. New strategy The original idea of virtual core is: N cores C-task Remote cores Computation Offloading N+1 cores

13. New strategy(Cont.) 反其道而行 Close a core after offloading N cores C-task Remote cores Computation Offloading N-1 cores

14. Reason After offloading, the rest of the tasks will be scheduled to N cores. ◦ Should have better performance. ◦ Does not guarantee energy saving.  All the cores are still working! If we close a core after offloading ◦ Imagine that the computation-intensive task is non-preemptive, but consume zero power. ◦ Energy saving with little effect to (other tasks) performance.

15. However This is a theoretically strategy. Need to design some experiments to verify the strategy.