Jui-Hao Chiang

Introspection-based memory de-duplication and migration

Memory virtualization abstracts a physical machines memory resource and presents to the virtual machines running on it a piece of physical memory that could be shared, compressed and moved. To optimize the memory resource utilization by fully leveraging the flexibility afforded by memory virtualization, it is essential that the hypervisor have some sense of how the guest VMs use their allocated physical memory. One way to do this is virtual machine introspection (VMI), which interprets byte values in a guest memory space into semantically meaningful data structures. However, identifying a guest VMs memory usage information such as free memory pool is non-trivial. This paper describes a bootstrapping VM introspection technique that could accurately extract free memory pool information from multiple versions of Windows and Linux without kernel version-specific hard-coding, how to apply this technique to improve the efficiency of memory de-duplication and memory state migration, and the resulting improvement in memory de-duplication speed, gain in additional memory pages de-duplicated, and reduction in traffic loads associated with memory state migration.

Accurate clock synchronization for IEEE 802.11-based multi-hop wireless networks

Clock synchronization is an essential building block for many control mechanisms used in wireless networks, including frequency hopping, power management, and packet scheduling. Although the IEEE 802.11 standard [1] provides a clock synchronization mechanism for multi-hop wireless networks, it has well-documented accuracy problems [2], [3] because the beacon frames transmitted by nodes with faster clock are not prioritized at the MAC layer. This paper describes the design and implementation of the first known software-only solution that successfully eliminates the deficiency of IEEE 802.11s clock synchronization mechanism when operating on multihop wireless networks without requiring any hardware/protocol modifications. The key idea of this solution is to periodically arrange for a node to become the fastest node in the network by jumping its clock with a substantial amount, and force other nodes to synchronize their clocks with this leading node by virtue of IEEE 802.11s native clock synchronization mechanism. Empirical measurements of a working implementation of the proposed algorithm on a multi-hop wireless network testbed conclusively demonstrates its effectiveness in removing IEEE 802.11s clock synchronization accuracy problem.

Hypervisor Support for Efficient Memory De-duplication

Memory de-duplication removes the memory state redundancy among virtual machines that run on the same physical machine by identifying common memory pages shared by these virtual machines and storing only one copy for each of common memory pages. A standard approach to identifying common memory pages is to hash the content of each memory page, and compare the resulting hash values. In a virtualized server, only the hyper visor is in a position to compute the hash value of every physical memory page on the server, but the memory de-duplication engine is best implemented outside the hyper visor for flexibility and simplicity reasons. A key design issue in the memory de-duplication engine is to minimize the performance impact of these hashing computations on the running VMs. To reduce this impact, memory page hashing should be performed with low overhead and when the CPU is idle. This paper describes why existing hyper visors do not provide adequate support for our memory de-duplication engine, how a new primitive called deferrable aggregate hyper call (DAH) fills the need, and what the resulting performance improvement is.

Physical Machine State Migration

A powerful functionality enabled by modern virtualization technologies is the ability to move a virtual machine (VM) from one physical machine to another, which enables unprecedented flexibility for system fault tolerance and load balancing. However, no similar capability exists for physical machines. This paper describes the first known successful implementation of migrating a physical machines state from one physical Linux machine to another. This physical machine state migration (PMSM) capability greatly decreases the amount of disruption due to scheduled shut-down for non-virtualized physical machines, and is more challenging than VM migration because it cannot rely on a separate piece of software to perform the state transfer, e.g., the hyper visor in the case of VM migration. The PMSM prototype described in this paper is adapted from Linuxs hibernation facility. The current PMSM prototype can migrate a physical machine running the MySQL DBMS server under 7 seconds.

A networked robot system for wireless network emulation

A major barrier to advancing modern wireless networking research is the lack of an effective wireless network simulation platform that simultaneously offers high fidelity, scalability, reproducibility and ease of use. MiNT [8], [7] is an innovative wireless network emulation platform that is specifically designed to satisfy all these desirable properties. To support reconfigurable network topology and wireless node mobility, MiNT is built on a networked robot system that carries wireless networking equipments and is designed to be completely tetherless, capable of supporting 24X7 operation, and low-cost. This paper describes the design, implementation and evaluation of this networked robot system. Each robot node in MiNT is an iRobots Roomba, which is modified to house an embedded PC equipped with multiple wireless networking interfaces and to re-charge the embedded PC through Roombas built-in self-charging mechanism. For robot navigation and movement, MiNTs networked robot system supports a computer vision-based robot positioning mechanism and a collision avoidance-driven trajectory planning component. Finally, MiNT provides an interactive control interface and visualization interface to give users real-time visibility into and full control over the MiNT testbed.

Bootstrapped migration for Linux OS

Modern virtualization technologies have a powerful ability to move a virtual machine (VM) from one physical machine to another, which enables unprecedented flexibility for system fault tolerance and load balancing. However, for physical machines there is no similar capability. This paper describes the detailed design of migrating a physical machines state from one physical Linux machine to another. This BOotstrapped Migration for Linux OS (BOMLO) capability avoids scheduled shut-down for the maintenance of non-virtualized physical machine and therefore greatly decreases the service disruption time. BOMLO is more challenging than VM migration because there is no separate piece of software to perform the state migration, e.g., the hypervisor in the case of VM migration. In this paper, we adapted the Linuxs hibernation facility to develop 3 schemes for BOMLO: swap disk-based, memory-to-memory, and iterative memory-to-memory migration.

Memory Pressure Balancing on Virtualized Servers

The effectiveness of a modern hyper visor on a virtualized server is measured by its consolidation ratio, which is defined as the maximum number of virtual machines (VM) that can run on a physical server without performance degradation. A key factor in determining a hyper visors consolidation ratio is its effectiveness in fairly distributing a virtualized servers physical memory resource among the VMs running on it when the total memory demand of these VMs exceeds the servers physical memory size. This paper describes the design, implementation and evaluation of a memory pressure balancer called Gatto that constantly measures the working set size of each VM running on a virtualized server, and exploits this information to distribute the servers physical memory resource so as to balance the memory pressures experienced by these VMs. Gattos memory pressure balancing mechanism could be generalized and applied to achieve memory quality of service (QoS) guarantee onmultitenant virtualized servers.

Memory Reclamation and Compression Using Accurate Working Set Size Estimation

Minimizing the total amount of physical memory consumption of the virtual machines (VM) concurrently running on a physical server is a key to improving a hyper visors consolidation ratio, defined as the maximum number of VMs that can run on a physical server without performance degradation. This paper describes the design, implementation and evaluation of a memory resource manager called Gatun that constantly measures the working set size of each running VM, and exploits this information to make the best of the available physical memory on a physical server. The per-VM working set size information allows Gatun to reclaim only unused physical memory from each running VM without negatively affecting its performance, and to compress the right subset of memory pages for each VM to reduce its memory pressure to the maximal extent possible. Compared with a state-of-the-art commercial hyper visor, Gatun is able to make noticeably more efficient utilization of a virtualized servers physical memory because of its ability to capture and leverage the per-VM working set size information.

Implementation and evaluation of a mobile tetherless VoIP/PSTN gateway

A voice-over-IP (VoIP) gateway bridges IP-based packet-switched networks (i.e. Internet) with public circuit-switched telephone networks (i.e. PSTN). The key building block of a VoIP gateway is a telephony card that interfaces with the PSTN and converts signals from the PSTN to bits that can be manipulated by a computer and vice versa. Because commercially available telephony cards only work with wired PSTN lines, almost all existing VoIP gateways are tethered and therefore do not support the kind of mobility enabled by modern wireless communications technology. This paper describes the implementation and evaluation of a mobile VoIP gateway called WGate that is designed specifically to bridge wireless VoIP clients and cellular phones, and can thus be easily deployed on demand in particular geographical locations. The key innovation of WGate is the ability to use a Bluetooth link as a wireless backplane by exploiting the Hands-Free profile of the Bluetooth protocol stack and eventually turning a set of commodity bluetooth-capable cell phones into a multi-port telephony card. Empirical measurements on a working prototype show that this approach can scale a VoIP gateway up to 8 cell phones because state-of-the-art Bluetooth adapters can only support up to 8 simultaneous Synchronous Connection-Oriented (SCO) connections when they operate in physically close proximity.