Hitoshi Mitake

Composition kernel: a multi-core processor virtualization layer for rich functional smart products

Future ambient intelligence environments will embed powerful multi-core processors to compose various functionalities into a smaller number of hardware components. This makes the maintainability of intelligent environments better because it is not easy to manage massively distributed processors. A composition kernel makes it possible to compose multiple functionalities on a multi-core processor with the minimum modification of OS kernels and applications. A multi-core processor is a good candidate to compose various software developed independently for dedicated processors into one multi-core processor to reduce both the hardware and development cost. In this paper, we present SPUMONE which is a composition kernel for developing future smart products.

Using Virtual CPU Migration to Solve the Lock Holder Preemption Problem in a Multicore Processor-Based Virtualization Layer for Embedded Systems

When a real-time OS (RTOS) and a symmetric multiprocessing general purpose OS (SMP GPOS) are executed on the same multicore processor, there is a possibility to cause the lock holder preemption (LHP) problem, which is a well known problem of the sources of the performance degradation on an SMP GPOS. The problem occurs when a kernel mode thread holding a lock in a SMP GPOS is preempted by other OSes if these OSes share the same physical core. The existing solution does not take into account real-time responsiveness so it is not suitable to use in embedded systems. The paper proposes two new techniques to avoid the LHP problem for ensuring both the real-time responsiveness of real-time OS and the high throughput of SMP GPOS. The new proposed techniques have been implemented on our virtualization layer called SPUMONE, and we measured the results showing that the proposed new techniques reduce the LHP problem without degrading the real-time responsiveness.

A Light-Weighted Virtualization Layer for Multicore Processor-Based Rich Functional Embedded Systems

In this paper, we introduce a lightweight processor abstraction layer named SPUMONE. SPUMONE provides virtual CPUs for respective guest OSes, and schedules them according to their priorities. In a typical case, SPUMONE schedules Linux with a low priority and an RTOS with a high priority. We first discuss why the traditional virtual machine monitor design is not appropriate for embedded systems, and how the features of SPUMONE allow us to design modern complex embedded systems with less efforts. Then, we describe two features of SPUMONE for the real-time resource management. SPUMONE also offers a novel mechanism to protect a critical component from malicious programs injected into the GPOS kernel.

Improving GPOS Real-Time Responsiveness Using vCPU Migration in an Embedded Multicore Virtualization Platform

In this paper, a vCPU (virtual CPU) migration mechanism in order to improve real-time responsiveness in a GPOS (General Purpose Operating System) is presented in the embedded multicore virtualization platform and can also be applied to CPS environment. Virtualization technique is recently emerging as a useful solution for the embedded system, because it can provide real-time handling ability through a RTOS (Real Time Operating System), and use a GPOS to deal with other tasks like windowing or entertaining services. However, tasks in GPOS now also need some degree of real-time services from the system. For example, the audio or video tasks. Unfortunately, in a traditional virtualization platform, a virtualization layer always gives RTOS vCPU higher priority and preempts the execution of GPOS. The reason for this phenomenon is that the underlying virtualization layer has no additional scheduling information provided. Therefore, a kernel module in the GPOS is added in our virtualization system to export and boost a GPOS vCPU contexts which needs higher priority against RTOS vCPU. At the same time, in order not to sacrifice the performance of the victim RTOS vCPU, a vCPU migration mechanism is added to our virtualization system, and migrates the RTOS vCPU to a low-loading CPU when this vCPU is preempted. Performance improvement of GPOSs real-time responsiveness is also given while a detailed analysis of the overhead of the RTOS vCPU is performed as well. The result showed that the migration overhead of a RTOS vCPU is under an acceptable level. This also means that one can use our approach to improve the GPOSs performance, while keeping RTOSs real-time responsiveness at the same time.

Hardware-Assisted Reliability Enhancement for Embedded Multi-core Virtualization Design

In this paper, we propose a virtualization architecture for the multi-core embedded system to provide more system reliability and security while maintaining the same performance without introducing additional special hardware supports or having to implement complex protection mechanism in the virtualization layer. Virtualization has been widely used in embedded systems, especially in consumer electronics, albeit itself is not a new technique, because there are various needs for both GPOS (General Purpose Operating System) and RTOS (Real Time Operating System). The surge of the multi-core platform in the embedded system also helps the consolidation of the virtualization system for its better performance and lower power consumption. Embedded virtualization design usually uses two kinds of approaches. The first one is to use the traditional VMM, but it is too complicated for use in the embedded environment if there is no additional special hardware support. The other is the use of the micro kernel which imposes a modular design. The guest systems, however, would suffer from considerable amount of modifications because the micro kernel lets the guest systems to run in user space. For some RTOSes and theirs applications originally running in kernel space, it makes this approach more difficult to work because a lot of privileged instructions are used in those codes. To achieve better reliability and keep the virtualization layer design light weighted, a common hardware component adopted in the multi-core embedded processors is used in this work. In the most embedded platforms, vendors provide additional on-chip local memory for each physical core and these local memory areas are private only to their cores. By taking this memory architectures advantage, we can mitigate above-mentioned problems at once. We choose to re-map the virtualization layers program called SPUMONE, which it runs all its guest systems in kernel space, on the local memory. By doing so, it can provide additional reliability and security for the entire system because the SPUMONEs design in a multi-core platform has each instance being installed on a separated processor core which is different from the traditional virtualization layer design and the content of each SPUMONE is inaccessible to each others. We also achieve this goal without bringing any overhead to the overall performance.

Coexisting real-time OS and general purpose OS on an embedded virtualization layer for a multicore processor

Porting operating systems to a virtualization layer produces a semantic gap because the assumptions that guest OSes rely on may not be ensured. On multi-core environments, this gap can cause the fatal performance degradations. The lock holder preemption (LHP) problem is a well known example of the sources of the performance degradation. It occurs when a thread holding a spin lock in an OS kernel is preempted by other OS kernels. Some previous proposals can avoid this problem, but none of them cares about the real-time responsiveness of guest OSes. Therefore the approaches are not suitable for embedded systems. We have developed a new technique for avoiding the LHP problem. The approach can ensure both the real-time responsiveness of RTOS and the high throughput of GPOS that supports shared memory multi-processors. This paper introduces the basic approach of our new technique and its experimental results. The results show that our new technique can make RTOS and GPOS coexist without degrading the real-time latency and is suitable to be applied to modern high performance multi-core processor based real-time embedded systems.

Composition Kernel: A Multi-core Processor Virtualization Layer for Highly Functional Embedded Systems

In this paper, we propose a composition kernel where multiple OS kernels are running on top of a very thin hardware abstraction layer. A composition kernel can reduce the engineering cost of developing an embedded system by reusing existing OS kernels and application with minimum modification without assuming special hardware supports.

Improving GPOS real-time responsiveness using vCPU migration in an embedded multicore virtualization platform

In this paper, a vCPU (virtual CPU) migration mechanism in order to improve real-time responsiveness in a GPOS (General Purpose Operating System) is presented in the embedded multicore virtualization platform and can also be applied to CPS environment. Virtualization technique is recently emerging as a useful solution for the embedded system, because it can provide real-time handling ability through a RTOS (Real Time Operating System), and use a GPOS to deal with other tasks like windowing or entertaining services. However, tasks in GPOS now also need some degree of real-time services from the system. For example, the audio or video tasks. Unfortunately, in a traditional virtualization platform, a virtualization layer always gives RTOS vCPU higher priority and preempts the execution of GPOS. The reason for this phenomenon is that the underlying virtualization layer has no additional scheduling information provided. Therefore, a kernel module in the GPOS is added in our virtualization system to export and boost a GPOS vCPU contexts which needs higher priority against RTOS vCPU. At the same time, in order not to sacrifice the performance of the victim RTOS vCPU, a vCPU migration mechanism is added to our virtualization system, and migrates the RTOS vCPU to a low-loading CPU when this vCPU is preempted. Performance improvement of GPOSs real-time responsiveness is also given while a detailed analysis of the overhead of the RTOS vCPU is performed as well. The result showed that the migration overhead of a RTOS vCPU is under an acceptable level. This also means that one can use our approach to improve the GPOSs performance, while keeping RTOSs real-time responsiveness at the same time.

Analyzing The Tradeoff Between Throughput and Latency in Multicore Scalable In-Memory Database Systems

In this paper, we present a tradeoff between throughput and latency in multicore scalable in-memory database systems by showing the results of a performance evaluation and analysis of Masstree, a state-of-the-art multicore scalable data structure that forms the foundation of a variety of multicore scalable database systems. The key technique to make Masstree scalable is an advanced concurrency control technique. Such a technique reduces cache line contention between cores and contributes to high throughput and scalability. However, surprisingly, the worst case latency of the Masstree-based key-value storage system was more than 10 times larger than the score of the memcached system. To detect the main source of the high latency spikes, we analyzed the concurrency control techniques of Masstree. As a result, we found that read-copy update (RCU), an important technique that enables scalability in Masstree, becomes the dominant factor in the high latency spikes. We present a straightforward approach to resolve the latency spikes. In addition, we also show the limitation of the straightforward approach and possible future directions of essential solutions.