Lior Amar

An organizational grid of federated MOSIX clusters

MOSIX is a cluster management system that uses process migration to allow a Linux cluster to perform like a parallel computer. Recently it has been extended with new features that could make a grid of Linux clusters run as a cooperative system of federated clusters. On one hand, it supports automatic workload distribution among connected clusters that belong to different owners, while still preserving the autonomy of each owner to disconnect its cluster from the grid at any time, without sacrificing migrated processes from other clusters. Other new features of MOSIX include grid-wide automatic resource discovery; a precedence scheme for local processes and among guest processes (from other clusters); flood control; a secure run-time environment (sandbox) which prevents guest processes from accessing local resources in a hosting system, and support of cluster partitions. The resulting grid management system is suitable to create an intra-organizational high-performance computational grid, e.g., in an enterprise or in a campus. The paper presents enhanced and new features of MOSIX and their performance.

Combining Virtual Machine migration with process migration for HPC on multi-clusters and Grids

The renewed interest in virtualization gives rise to new opportunities for running high performance computing (HPC) applications on clusters and grids. These include the ability to create a uniform (virtual) run-time environment on top of a multitude of hardware and software platforms, and the possibility for dynamic resource allocation towards the improvement of process performance, e.g., by virtual machine (VM) migration as a means for load-balancing. This paper deals with issues related to running HPC applications on multi-clusters and grids using VMware, a virtualization package running on Windows, Linux and OS X. The paper presents the ldquoJobrunrdquo system for transparent, on-demand VM launching upon job submission, and its integration with the MOSIX cluster and grid management system. We present a novel approach to job migration, combining VM migration with process migration using Jobrun, by which it is possible to migrate groups of processes and parallel jobs among different clusters in a multi-cluster or in a grid. We use four real HPC applications to evaluate the overheads of VMware (both on Linux and Windows), the MOSIX cluster extensions and their combination, and present detailed measurements of the performance of Jobrun.

The MOSIX Direct File System Access Method for Supporting Scalable Cluster File Systems

MOSIX is a cluster management system that supports preemptive process migration. This paper presents the MOSIX Direct File System Access (DFSA), a provision that can improve the performance of cluster file systems by allowing a migrated process to directly access files in its current location. This capability, when combined with an appropriate file system, could substantially increase the I/O performance and reduce the network congestion by migrating an I/O intensive process to a file server rather than the traditional way of bringing the files data to the process. DFSA is suitable for clusters that manage a pool of shared disks among multiple machines. With DFSA, it is possible to migrate parallel processes from a client node to file servers for parallel access to different files. Any consistent file system can be adjusted to work with DFSA. To test its performance, we developed the MOSIX File-System (MFS) which allows consistent parallel operations on different files. The paper describes DFSA and presents the performance of MFS with and without DFSA.

An On-line Algorithm for Fair-Share Node Allocations in a Cluster

Proportional (fair) share schedulers are designed to provide applications with predefined portions of system resources. Single node operating systems use context-switch (preemption) to dynamically allocate the CPU(s) to running processes. This paper presents an online algorithm for proportional share allocations of nodes in a cluster, in a fashion that resembles a single-node system. The algorithm relies on preemptive process migrations for dynamic allocations of nodes to users. The paper presents the algorithm and its performance on a MOSIX organizational Grid with 60 nodes. We show that proportional share allocations can be achieved in a relatively short time (minutes).

The Power of Preemption in Economic Online Markets

In distributed computer networks where resources are under decentralized control, selfish users will generally not work towards one common goal, such as maximizing the overall value provided by the system, but will instead try to strategically maximize their individual benefit. This shifts the scheduling policy in such systems --- the decision about which user may access what resource --- from being a purely algorithmic challenge to the domain of mechanism design. In this paper we will showcase the benefit of allowing preemptionin such economic online settings regarding the performance of market mechanisms by extending the Decentralized Local Greedy Mechanism of Heydenreich et al. [11]. This mechanism was shown to be 3.281-competitive with respect to total weighted completion time if the players act rationally. We show that the preemptive versionof this mechanism is 2-competitive. As a by-product, preemption allows to relax the assumptions on jobs upon which this competitiveness relies. In addition to this worst case analysis, we provide an in-depth empirical analysis of the average case performanceof the original mechanism and its preemptive extension based on real workload traces. Our empirical findings indicate that introducing preemption improves both the utility and the slowdown of the jobs. Furthermore, this improvement does not come at the expense of low-priority jobs.

On the importance of migration for fairness in online grid markets

Computational grids oer users a simple access to tremendous computer resources for solving large scale computing problems. Traditional performance analysis of scheduling algorithms considers overall system performance while fairness analysis focuses on the individual performance each user receives. Until recently, only few grids and cluster systems provided preemptive migration (e.g. [2]), which is the ability of dynamically moving computational tasks across machines during runtime. The emergent technology of virtualization (e.g. [4]) provides o-the-shelf support for migration, thus making the use of this feature more accessible (even across dierent OS’s). In this paper, we study the close relation between migration and fairness. We present fairness and quality of service properties for economic online scheduling algorithms. Under mild assumptions we show that it is impossible to achieve these properties without the use of migration. On the other hand, if zero cost migration is used, then these properties can be satised.

Harnessing migrations in a market-based grid OS

Applying economic principles to grids is deemed promising to improve the overall value provided by such systems. End users can influence the allocation of resources by reporting valuations for these resources. Current market-based schedulers, however, are static, assume the availability of complete information about jobs (in particular with respect to processing times), and do not make use of the flexibility offered by advanced computing systems. In this paper, we present the implementation of economic resource allocation principles into MOSIX, a state-of-the-art management system for computing clusters and multi-cluster organizational grids. The system is designed so as to be able to work in large-scale settings with selfish agents. Facing incomplete information about jobspsila characteristics, it dynamically allocates jobs to computing machines by leveraging preemption and job migration, two distinct features offered by MOSIX. We validate and showcase the behavior of our economic model by means of experiments in the real system.