1. Project Overview 2014/05/05 1

2. Current Project “Research on Embedded Hypervisor Scheduler Techniques” ◦ Design an energy-efficient scheduling mechanism in virtualized environment. ◦ Assume the hardware platform is asymmetric multi-core.  big.LITTLE core architecture. 2

3. big.LITTLE Core Architecture Developed by ARM in Oct. 2011. Combine two kinds of architecturally compatible cores. To create a multi-core processor that can adjust better to dynamic computing needs and use less power than clock scaling alone. big cores are more powerful but power-hungry, while LITTLE cores are low-power but (relatively) slower. 3

4. Three Types of Models Cluster migration CPU migration(In-Kernel Switcher) Heterogeneous multi-processing (global task scheduling)

5. Type 1: Cluster Migration Either big or LITTLE cores are used simultaneously.

6. Type 2: CPU Migration Logical CPU: a pair of big and LITTLE core. Only one of the two cores in a pair is powered up and processing tasks at a time.

7. Type 3: HMP All the big and LITTLE cores can be used at the same time.

8. Task Scheduling in Asymmetric Multi-cores Task should be distributed unevenly. ◦ Only critical tasks should execute on big cores in order to minimize power consumption. ◦ Different from traditional SMP scheduling. ◦ Needs to design new scheduling algorithms. 8

9. Asymmetric Multi-core in Datacenter Asymmetric multi-core is not limited to hand-held devices or embedded systems. There will be servers with asymmetric cores in a datacenter. ◦ Virtualized environment in datacenter. 9

10. OS Kernel GUEST2 Android Framework Scheduler VCPU OS Kernel GUEST2 Android Framework Scheduler VCPU 10 ARM Cortex-A15 ARM Cortex-A7 OS Kernel GUEST1 Android Framework Scheduler VCPU Hypervisor vCPU Scheduler Performance Power- saving Low computing resource requirement High computing resource requirement If Guest OS scheduler is not big.LITTLE-aware, it will assign tasks to vCPUs evenly in order to achieve load balancing. Task 1 Task 2 Task 3 Task 4 Hypervisor vCPU scheduler will assign vCPUs evenly to physical ARM cores since it is not big.LITTLE-aware. Cannot take advantage on big.LITTLE core architeture Current Hypervisor Architecture and Problem

11. OS Kernel GUEST2 Android Framework Scheduler VCPU 11 ARM Cortex-A15 ARM Cortex-A7 OS Kernel GUEST1 Android Framework Scheduler VCPU Hypervisor Performance Power- saving If Guest OS scheduler is not big.LITTLE-aware, it will assign tasks to vCPUs evenly in order to achieve load balancing. Cannot take advantage on big.LITTLE core architeture Task 1 Task 2 Task 3 Task 4 Both on big core Ot both on LITTLE core b-L vCPU Scheduler Even if hypervisor vCPU scheduler is big.LITTLE- aware, it will schedule these vCPUs to either big cores or LITTLE cores since they have the same loading. Current Hypervisor Architecture and Problem(Cont.)

12. Challenge The hypervisor scheduler cannot take advantage of big.LITTLE architecture if the scheduler inside guest OS is not big.LITTLE aware. 12

13. Our Solution Apply VM introspection(VMI) to retrieve the process list in a VM. ◦ VMI is a technique that allows the hypervisor to inspect the contents of the VM in real-time. Modify the CPU masks of tasks in the VM in order to create an illusion of “big vCPU” and “LITTLE vCPU”. Hypervisor scheduler can assign the vCPU to corresponding big or LITTLE cores. 13

14. Linaro Linux Kernel GUEST2 Android Framework Scheduler VCPU 14 ARM Cortex-A15 ARM Cortex-A7 OS Kernel GUEST1 Android Framework Scheduler VCPU Hypervisor Performance Power- saving OS Kernel GUEST2 Android Framework Scheduler VCPU Low computing resource requirement High computing resource requirement Task 2 Task 4 VM Introspector b-L vCPU Scheduler VM Introspector gathers task information from Guest OS Task-to- vCPU Mapper Modify the CPU mask of each task according to the task information from VMI [1|0] [0|1] Treat this vCPU as LITTLE core since tasks with low computing requirement are scheduled here. Hypervisor vCPU scheduler will schedule big vCPU to A15, and LITTLE vCPU to A7. VCPU Task 3 Task 1 Hypervisor Architecture with VMI

15. OS Kernel GUEST2 Android Framework Scheduler VCPU 15 ARM Cortex-A15 ARM Cortex-A7 OS Kernel GUEST1 Android Framework Scheduler VCPU Hypervisor Performance Power- saving Task 2 Task 4 VM Introspector b-L vCPU Scheduler Task-to- vCPU Mapper [1|0] [0|1] Hypervisor vCPU scheduler will schedule big vCPU to A15, and LITTLE vCPU to A7. VCPU Task 3 Task 1 VCPU Task 1 [1|1] Guest OS 2 has two task with low computing requirement VM Introspector gathers task information from Guest OS Modify the CPU mask of each task according to the task information from VMI Task 2 Treat this vCPU as LITTLE core since tasks with low computing requirement are scheduled here. Guest OS 1 has two task with high computing requirement and two task with low computing requirement Hypervisor Architecture with VMI(Cont.)

16. Current Status Implementing the proposed architecture. ◦ Trying to enable VMI on Xen 64 bit. Developing new scheduling algorithms for big.LITTLE core. 16

17. Q&A 17