7610617
High Performance VMM-Bypass I/O in Virtual Machines
Currently, I/O device virtualization models in virtual machine (VM) environments require involvement of a virtual machine monitor (VMM) and/or a privileged VM for each I/O operation, which may turn out to be a performance bottleneck for systems with high I/O demands, especially those equipped with modern high speed interconnects such as InfiniBand. 
 
In this paper, we propose a new device virtualization model called VMM-bypass I/O, which extends the idea of OS-bypass originated from user-level communication. Essentially, VMM-bypass allows time-critical I/O operations to be carried out directly in guest VMs without involvement of the VMM and/or a privileged VM. By exploiting the intelligence found in modern high speed network interfaces, VMM-bypass can significantly improve I/O and communication performance for VMs without sacrificing safety or isolation. 
 
To demonstrate the idea of VMM-bypass, we have developed a prototype called Xen-IB, which offers InfiniBand virtualization support in the Xen 3.0 VM environment. Xen-IB runs with current InfiniBand hardware and does not require modifications to existing user-level applications or kernel-level drivers that use InfiniBand. Our performance measurements show that Xen-IB is able to achieve nearly the same raw performance as the original InfiniBand driver running in a non-virtualized environment.
11127837
Nomad: migrating OS-bypass networks in virtual machines
Virtual machine (VM) technology is experiencing a resurgence due to various benefits including ease of management, security and resource consolidation. Live migration of virtual machines allows transparent movement of OS instances and hosted applications across physical machines. It is one of the most useful features of VM technology because it provides a powerful tool for effective administration of modern cluster environments. Migrating network resources is one of the key problems that need to be addressed in the VM migration process. Existing studies of VM migration have focused on traditional I/O interfaces such as Ethernet. However, modern high-speed interconnects with intelligent NICs pose significantly more challenges as they have additional features including hardware level reliable services and direct I/O accesses. In this paper we present Nomad, a design for migrating modern interconnects with the aforementioned features, focusing on cluster environments running VMs. We introduce a thin namespace virtualization layer to efficiently address location dependent resource handles and a handshake protocol which transparently maintains reliable service semantics during migration. We demonstrate our design by implementing a prototype based on the Xen virtual machine monitor and InfiniBand. Our performance analysis shows that Nomad can achieve efficient migration of network resources, even in environments with stringent communication performance requirements.
7089503
Supporting MPI-2 One Sided Communication on Multi-rail InfiniBand Clusters: Design Challenges and Performance Benefits
In cluster computing, InfiniBand has emerged as a popular high performance interconnect with MPI as the de facto programming model. However, even with InfiniBand, bandwidth can become a bottleneck for clusters executing communication intensive applications. Multi-rail cluster configurations with MPI-1 are being proposed to alleviate this problem. Recently, MPI-2 with support for one-sided communication is gaining significance. In this paper, we take the challenge of designing high performance MPI-2 one-sided communication on multi-rail InfiniBand clusters. We propose a unified MPI-2 design for different configurations of multi-rail networks (multiple ports, multiple HCAs and combinations). We present various issues associated with one-sided communication such as multiple synchronization messages, scheduling of RDMA (Read, Write) operations, ordering relaxation and discuss their implications on our design. Our performance results show that multi-rail networks can significantly improve MPI-2 one-sided communication performance. Using PCI-Express with two-ports, we can achieve a peak MPI_Put bidirectional bandwidth of 2620 Million Bytes/s, compared to 1910 MB/s for single-rail implementation. For PCI-X with two HCAs, we can almost double the throughput and reduce the latency to half for large messages.
11481204
Scheduling of MPI-2 one sided operations over InfiniBand
MPI-2 provides interfaces for one sided communication, which is becoming increasingly important in scientific applications. MPI-2 semantics provide the flexibility to reorder the one sided operations within an access epoch. Based on this flexibility, in this paper we try to improve the performance of one sided communication by scheduling one sided operations. We have come up with several re-ordering and aggregating schemes to achieve better network utilization. We have evaluated these schemes on both PCI-X and PCI-Express platforms. With re-ordering scheme, we see an improvement in the throughput up to 76%, latency up to 40%. With aggregation scheme, we observe an improvement of 44% and 42% for MPI/spl I.bar/Put and MPI/spl I.bar/Get latency respectively on PCI-Express platform.
2376785
Designing Efficient Asynchronous Memory Operations Using Hardware Copy Engine: A Case Study with I/OAT
Memory copies for bulk data transport incur large overheads due to CPU stalling, small register-size data movement, etc. Intel's I/O Acceleration Technology offers an asynchronous memory copy engine in kernel space which alleviates such overheads. In this paper, we propose a set of designs for asynchronous memory operations in user space for both single process (as an offloaded memcpy()) and lPC using the copy engine. We analyze our design based on overlap efficiency, performance and cache utilization. Our microbenchmark results show that using the copy engine for performing memory copies can achieve close to 87% overlap with computation. Further, the copy engine improves the copy latency of bulk memory data transfers by 50% and avoids cache pollution effects. With the emergence of multi-core architectures, the support for asynchronous memory operations holds a lot of promise in reducing the gap between the memory and processor performance.
2763282
Can memory-less network adapters benefit next-generation infiniband systems?
InfiniBand is emerging as a high-performance interconnect. It is gaining popularity because of its high performance and open standard. Recently, PCI-Express, which is the third generation high-performance I/O bus used to interconnect peripheral devices, has been released. The third generation of InfiniBand adapters allow applications to take advantage of PCI-Express. PCI-Express offers very low latency access of the host memory by network interface cards (NICs). Earlier generation InfiniBand adapters used to have an external DIMM attached as local NIC memory. This memory was used to store internal information. This memory increases the overall cost of the NIC. In this paper we design experiments, analyze the performance of various communication patterns and end applications on PCI-Express based systems, whose adapters can be chosen to run with or without local NIC memory. Our investigations reveal that on these systems, the memory fetch latency is the same for both local NIC memory and host memory. Under heavy I/O bus usage, the latency of a scatter operation increased only by 10% and only for message sizes IB -4 KB. These memory-less adapters allow more efficient use of overall system memory and show practically no performance impact (less than 0.1%) for the NAS parallel benchmarks on 8 processes. These results indicate that memory-less network adapters can benefit next generation InfiniBand systems.
12648516
Experiments in impulsive manipulation
In this paper, we present the results of our experimental effort in one form of impulsive manipulation: tapping. Our previous work studied the mechanics of tapping a planar object which then slides on a support surface, coming to rest due to friction. This work addresses the practical issues in creating a system which uses this mode of manipulation. We begin with the design of tapping devices-end effecters designed to deliver an impulse to an object, and report some of the issues we have found to be important in their design. Our next step was to perform single-tap experiments in order to fit and evaluate the models of impact and sliding. These experiments have shown that objects rotate less than predicted; we have found that the addition of a scaling factor for the torque due to friction enables the models to predict object motion reasonably well. In order to do positioning experiments, we developed a number of planning methods (or feedback control strategies) to compensate for errors in modeling, parameters, and actuation. These planning methods were successfully used to demonstrate a positioning task. We also have experimentally demonstrated that tapping can be used to position an object more precisely than the manipulator can position the tapping device. We offer some sensitivity analysis in support of this result.
40011370
Contextual Knowledge Representation, Retrieval and Interpretation in Multimedia e-Learning
In highly interactive modern multimedia e-learning environments, current e-learning support products based on basic information management technologies are not able to support semantic-based knowledge management and communication beyond heterogeneous multimedia learning resources. Much of desired intelligent e-learning functionality needs further research and technical developments with semantic context-awareness. Proposed framework in this paper is expected to improve the current isolated learning management status, by making the most use of related learning information, and enabling flexible knowledge retrieval, communication and transfer between instructors and learners. To work with related existing e-learning content description standards and enable a semantic-based interactive learning environment, this paper explores a set of novel contextual knowledge discovery and reuse techniques. Based on knowledge communication model analysis in university e-learning, a contextual knowledge representation model is presented. Corresponding knowledge retrieval and semantic knowledge interpretation techniques are presented afterwards towards supporting pedagogical learning approaches such as scenario-based learning.
2799741
Towards integrating semantics of multi-media resources and processes in e-Learning
Internet-based e-Learning has experienced a boom and bust situation in the past 10 years [32]. To bring in new forces to knowledge-oriented e-Learning, this paper addresses the semantic integration issue of multi-media resources and learning processes with theoretical learning supports in an integrated framework. This paper proposes a context-mediated approach that aims to enable semantic-based inter-operations across knowledge domains, even across the WWW and the Semantic Web [8]. The proposed semantic e-Learning framework enables intelligent operations of heterogeneous multi-media contents based on a generic semantic context intermediation model. This framework supports intelligent e-Learning with a knowledge network for knowledge object visualization, an enhanced Kolb's learning cycle [31] to guide learning practices, and a learning health care framework for personalized learning.
18025478
Facilitate knowledge communications
With current multimedia information management techniques, the knowledge communications among users in multimedia e-Learning environments are still limited at a relative low single type media servicing level. New developments in multimedia knowledge discovery, representation and integration are needed to improve the intelligence of the knowledge management and communications at the semantic level. This paper proposes a novel contextual knowledge management framework to improve the current isolated learning information retrieval and communication status, by enabling flexible knowledge representation beyond heterogeneous multimedia learning resources and facilitating multilevel knowledge communications between instructors and learners. Based on knowledge communication model analysis in university e-Learning environments, a contextual knowledge representation model is presented. Corresponding knowledge retrieval techniques are discussed afterwards. To demonstrate the proposed concepts and techniques, a case study in a virtual scenario-based learning environment shows how the presented framework works with existing e-Learning content description standards and multimedia information retrieval techniques, and consequently enables a semantic-based interactive learning environment.
416932
Parts Feeding on a Conveyor with a One Joint Robot
Abstract. This paper explores a method of manipulating a planar rigid part on a conveyor belt using a robot with just one joint. This approach has the potential of offering a simple and flexible method for feeding parts in industrial automation applications. In this paper we develop a model of this system and of a variation which requires no sensing. We have been able to characterize these systems and to prove that they can serve as parts feeding devices for planar polygonal parts. We present the planners for these systems and describe our implementations.