Sirocco: cost-effective fine-grain distributed shared memory

Software fine-grain distributed shared memory (FGDSM) provides a simplified shared-memory programming interface with minimal or no hardware support. Originally software FGDSMs targeted uniprocessor-node parallel machines. This paper presents Sirocco, a family of software FGDSMs implemented on a network of low-cost SMPs. Sirocco takes full advantage of SMP nodes by implementing inter-node sharing directly in hardware and overlapping computation with protocol execution. To maintain correct shared-memory semantics, however SMP nodes require mechanisms to guarantee atomic coherence operations. Multiple SMP processors may also result in contention for shared resources and reduce performance. SMP nodes also impact the cost trade-off. While SMPs typically charge higher price-premiums, for a given system size SMP nodes substantially reduce networking hardware requirement as compared to uniprocessor nodes. In this paper, we ask the question “Are SMPs cost-effective building blocks for software FGDSM?” We present experimental measurements on Sirocco implementations ranging from an all-software system to a system with minimal hardware support. Together with simple cost models we show that low-cost SMP nodes: (i) result in competitive performance with uniprocessor nodes, (ii) substantially reduce hardware requirement and are more cost- effective than uniprocessor nodes, (iii) significantly benefit from hardware support for coherence operations, and (iv) are especially beneficial for FGDSMs with high-overhead coherence operation

UNIVERSITY OF WISCONSIN—MADISON

Shared memory, one of the most popular models for programming parallel platforms, is becoming ubiquitous both in low-end workstations and high-end servers. With the advent of low-latency networking hardware, clusters of workstations strive to offer the same processing power as high-end servers for a fraction of the cost. In such environments, shared memory has been limited to page-based systems that control access to shared memory using the memory’s page protection to implement shared memory coherence protocols. Unfortunately, false sharing and fragmentation problems force such systems to resort to weak consistency shared memory models that complicate the shared memory programming model. This thesis studies fine-grain distributed shared memory (FGDSM) systems on networks of workstations to support shared memory and it explores the issues involved in the implementation of FGDSM systems on networks of commodity workstations running commodity operating systems. FGDSM systems rely on fine-grain memory access control to selectively restrict reads and writes to cache-block-sized memory regions. The thesis presents Blizzard, a family of FGDSM systems running on a network of workstations. Blizzard supports the Tempes

Address Translation Mechanisms in Network Interfaces

Good network hardware performance is often squandered by overheads for accessing the network interface (NI) within a host. NIs that support user-level messaging avoid frequent operating system (OS) action yet unnecessary copying can still result in low performance. We explore improving application messaging performance by eliminating all unnecessary copies (minimal messaging). For minimal messaging, NIs must support address translation and must do so more richly than has been done in the past. NI address translation should flexibly support higher-level abstractions, map all user space, exploit translation locality, and degrade gracefully when locality is poor. We classify NI address translation implementations based on where the lookup and the miss handling are performed (CPU or NI). We present alternative designs and we consider how they interact with the OS. We provide simulation results that evaluate the alternative design points and we demonstrate feasibility with a real implement..

Sirocco: Cost-Effective Fine-Grain Distributed . . .

Software fine-grain distributed shared memory (FGDSM) provides a simplified shared-memory programming interface with minimal or no hardware support. Originally software FGDSMs targeted uniprocessor-node parallel machines. This paper presents Sirocco, a family of software FGDSMs implemented on a network of low-cost SMPs. Sirocco takes full advantage of SMP nodes by implementing inter-node sharing directly in hardware and overlapping computation with protocol execution. To maintain correct shared-memory semantics, however, SMP nodes require mechanisms to guarantee atomic coherence operations. Multiple SMP processors may also result in contention for shared resources and reduce performance. SMP nodes also impact the cost trade-off. While SMPs typically charge higher price-premiums, for a given system size SMP nodes substantially reduce networking hardware requirement as compared to uniprocessor nodes. In this paper, we ask the question "are SMPs cost-effective building blocks for software..

The effect of time-dependent γ-pumping on buoyant magnetic structures

In this paper, we explore for the first time the interactions of the net downward, time-dependent, γ-pumping overlying an imposed layer of magnetic fluid, in a polytropic atmosphere. Our calculations show that an equipartition of energy, between the magnetic and kinetic components, must be reached for buoyancy-driven magnetic structures to rise into the pumping region. However, structures do not rise unhindered, as in a previous investigation. We show that the evolution and other features of the emerging magnetic flux structures are significantly affected by the temporal variation of the γ-pumping. The rate of emerging structures, the strength of magnetic concentrations and the extent to how far magnetic field can travel were all found to depend on the timescale of the γ-pumping