Virtual machine technology can enhance server utilization and consolidation on an individual physical machine. In a growing number of contexts, many of which re-quire high-performance networking inside of the system. ...
详细信息
The skyline operator has received considerable attention from the database community, due to its importance in many applications including multi-criteria decision making, preference answering, and so forth. In many ap...
详细信息
ISBN:
(纸本)9781424472611;9780769540597
The skyline operator has received considerable attention from the database community, due to its importance in many applications including multi-criteria decision making, preference answering, and so forth. In many applications where uncertain data a re inherently exist, i.e., data collected from different sources in distributed locations are usually with imprecise measurements, and thus exhibit kind of uncertainty. Taking into account the network delay and economic cost associated with sharing and communicating large amounts of distributed data over an internet, an important problem in this scenario is to retrieve the global skyline tuples from all the distributed local sites with minimum communication cost. Based on the well known notation of the probabilistic skyline query over centralized uncertain data, in this paper, for the first time, we propose the notation of distributed skyline queries over uncertain data. Furthermore, two communication- and computation-efficient algorithms are proposed to retrieve the qualified skylines from distributed local sites. Extensive experiments have been conducted to verify the efficiency and the effectiveness of our algorithms with both the synthetic and real data sets.
Different virtual educational experiments (VEEs) have different frameworks and implementations in different disciplines. How to integrate different VEEs into one unified supporting platform is a challenging problem. T...
详细信息
Different virtual educational experiments (VEEs) have different frameworks and implementations in different disciplines. How to integrate different VEEs into one unified supporting platform is a challenging problem. The key problem of this integration is how to build a unified mathematical model for VEEs of diversified disciplines. However, most existing multi-domain uniform modeling (MDUM) approaches such as Modelica are research-oriented and lack of real time interaction, which does not meet the requirement of virtual experiments that are user-oriented and highly interactive. To tackle above problem, a Modelica-based interactive scheduling mechanism (MISM) for VEE is proposed. In MISM, user-oriented interaction is based on a best step length algorithm and an interactive event step algorithm. The throughput is considered in the former and the real time interaction is resolved by the latter. Experimental results shows that the approaches presented can meet the requirements of VEEs efficiently.
CPU time accounting is a basis of performance measurement and process scheduling in operating system. Accounting operations are traditionally completed in timer interrupt handler since timer interrupt is periodically ...
详细信息
CPU time accounting is a basis of performance measurement and process scheduling in operating system. Accounting operations are traditionally completed in timer interrupt handler since timer interrupt is periodically delivered to OS. However, when virtualization introduced, the CPU time is shared by multiple virtual CPUs (i.e., VCPU for short) and the virtual timer interrupt is paused for those ones be scheduled out. This makes the time accounting be inaccurate, and we should consider new method for VM to provide a stable and reliable data source, especially for the hardware-assisted virtual machines (i.e., HVM for short) which are not aware of VMM. The key point of accurate CPU time accounting is to distinguish the time allocated to “this VCPU” and “other VCPUs”. Para-virtualization (i.e., PV for short) achieves this goal by modifying the timer handling routines. For HVM, we propose an accurate accounting method (named XenHVMAcct) within Xen virtual platform. XenHVMAcct is designed by using the mechanisms of virtual interrupt and loadable kernel module, without direct modifications to guest OS. Experimental results show that our accounting method is as accurate as the PV solution.
VM (virtual machine) scheduling is a fundamental topic of virtualization, and fairness is its important design goal. Most VMMs (virtual machine monitor) provide PS (proportional share) schedulers. A PS scheduler assig...
详细信息
VM (virtual machine) scheduling is a fundamental topic of virtualization, and fairness is its important design goal. Most VMMs (virtual machine monitor) provide PS (proportional share) schedulers. A PS scheduler assign a weight to every VM to declare the computational resource requirement, and VM is allocated CPU cycles proportional to weight. CPU-affinity is a property of VCPU (virtual CPU) to describe which PCPUs (physical CPU) it can run on. However, current definition of weight does not collaborate well with CPU-affinity. It behaves as if all PCPUs are available to all VMs. We expose the issue by using Xen’s Credit scheduler, and show that CPU cycles can be fairly allocated to VMs in the default free-mapping case (no affinity restriction), but not so in restricted-mapping cases (when affinities are configured). This fairness issue makes it necessary to extend the meaning of weight, so as to reflect the resource requirements in all cases. In this paper we reconcile the meaning of a domain’s weight with CPU-affinity, and improve Credit scheduler as an affinity-aware one. Experimental results show that our affinity-aware proportional share scheduler (named Credit-APS scheduler) brings a good fairness both in free-mapping and restricted-mapping cases.
With the rapid development of virtualization technology as well as the good performance of computer hardware, virtual machine is beginning to gradually increase the performance of display to meet the needs of desktop ...
详细信息
With the rapid development of virtualization technology as well as the good performance of computer hardware, virtual machine is beginning to gradually increase the performance of display to meet the needs of desktop users. However, there is a difference between the display mechanism in the virtual environment and the traditional environment. At present, more is focused on how to effectively and pertinently measure and assess the performance of display in virtualization environment. Taking consideration of the characteristics of display in the virtual environment, the virtual machine display performance evaluation system has following advantages: it can select a representative workload running on the VM in Domain U; make use of Tracing and Instrumentation to insert the record in the kernel of VM; log the relevant information; and then finally draw the performance-related parameters by the analysis of the recorder. This paper mainly depicts the underlying implementation details of the virtual display system in Xen and analyzes the display principle of Xen-based virtual machine. It also proposes a display latency performance model in Xen environment, which is named Vdismodel by verifying the reasonableness of the Vdismodel through a series of experiments and comparing the theoretical data and the measured data which are accessed by the virtual machine system performance evaluation.
As the degree of virtualization is growing considerably, improving performance of virtual machine environments motivates deeper investigation of the internal processes and performance implications of virtualization. S...
详细信息
As the degree of virtualization is growing considerably, improving performance of virtual machine environments motivates deeper investigation of the internal processes and performance implications of virtualization. Several tools are currently available to help analyze performance in virtual machine environments. However, all of these cannot support users to add their own trace information. In this paper, we present Xenrelay, a unified, efficient, and simple mechanism for transferring large amounts of data from guest domain kernel to privileged domain user-space. Xenrelay allows users (who trace subsystems of guest domain to analyze performance) to record and fast relay data between domains. We provide a case of Xenrelay's value in revealing behavior of virtualization. We build a block trace toolkit (using Xenrelay as an engine). This toolkit is used to track the block I/O virtualization procedures and evaluates overheads in the Xen environment. Our trace results identify that the main delay is the time of request transmission and block device operation. Besides, the results reveal impact of the I/O schedules on the disk performance.
With the development of client virtualization technology, it has become an important tendency to apply soft real-time applications in virtual environment. Currently, most schedulers in VMM (i.e., virtual machine monit...
详细信息
With the development of client virtualization technology, it has become an important tendency to apply soft real-time applications in virtual environment. Currently, most schedulers in VMM (i.e., virtual machine monitor) take the fairly sharing of processor resources and load balancing as a main concern, while show less regard to application diversity and I/O responsiveness. This would be unable to meet the requirement for latency-sensitive tasks, such as audio application. Audio stream may suffer from severe input buffer overrun or output buffer underrun, especially in the case that there is no real-time guarantee on virtualized clients under heavy load. In this paper, we introduce experiments to illustrate that current scheduler in Xen does a poor job in guaranteeing fluent audio playing, and then formulate the fluent playing conditions a scheduler should satisfy. A scheduling strategy with soft real-time support is proposed to improve the responsiveness of latency-sensitive guests. To implement our proposition, we extend the Credit scheduler by using flexible time slice and real-time priority. Our solution is audio-aware and capable of adjusting the real-time priority of guest domains adaptively, achieving a better experience for end-users. The experimental results show that audio glitches can be completely eliminated via our extended scheduler even when the system load is very high.
A virtual cluster consists of a multitude of virtual machines and software components that are doomed to fail eventually. In many environments, such failures can result in unanticipated, potentially devastating failur...
详细信息
A virtual cluster consists of a multitude of virtual machines and software components that are doomed to fail eventually. In many environments, such failures can result in unanticipated, potentially devastating failure behavior and in service unavailability. The ability of failover is essential to the virtual cluster's availability, reliability, and manageability. Most of the existing methods have several common disadvantages: requiring modifications to the target processes or their OSes, which is usually error prone and sometimes impractical; only targeting at taking checkpoints of processes, not whole entire OS images, which limits the areas to be applied. In this paper we present VirtCFT, an innovative and practical system of fault tolerance for virtual cluster. VirtCFT is a system-level, coordinated distributed checkpointing fault tolerant system. It coordinates the distributed VMs to periodically reach the globally consistent state and take the checkpoint of the whole virtual cluster including states of CPU, memory, disk of each VM as well as the network communications. When faults occur, VirtCFT will automatically recover the entire virtual cluster to the correct state within a few seconds and keep it running. Superior to all the existing fault tolerance mechanisms, VirtCFT provides a simpler and totally transparent fault tolerant platform that allows existing, unmodified software and operating system (version unawareness) to be protected from the failure of the physical machine on which it runs. We have implemented this system based on the Xen virtualization platform. Our experiments with real-world benchmarks demonstrate the effectiveness and correctness of VirtCFT.
Most of the current dynamic binary translation (DBT) systems are single-threaded and many orders of magnitude slower than native execution. Although multi-core processors are becoming more and more prevalent, the sing...
详细信息
Most of the current dynamic binary translation (DBT) systems are single-threaded and many orders of magnitude slower than native execution. Although multi-core processors are becoming more and more prevalent, the single-threaded architecture prevents these DBT systems from improving their performance by making full use of the parallel execution advantage. In this paper, we present the design and implementation of a multi-threaded DBT system, named MT-BTRIMER. MT-BTRIMER employs a master-slave multi-threaded architecture. We evaluate the MT-BTRIMER system across SPEC CINT 2000 and BYTEmark test suite. The results demonstrate that MT-BTRIMER can speculatively translate on average 60% of useful target code, and reduce the total runtime by nearly 30% compared with ST-BTRIMER which is a single-threaded DBT system.
暂无评论