Examinando por Autor "Ballesteros, Francisco J."

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Optimistic Semaphores with Non-deterministic Choice Operation for Heterogeneous Manycore Systems
(Wiley, 2015) Soriano-Salvador, Enrique; Guardiola Múzquiz, Gorka; Ballesteros, Francisco J.
The Nix operating system permits different roles to be assigned to the cores. One of the roles is to be able to run user-space code with no interrupts from the operating system, which is particularly useful for high-performance computing. System calls are especially expensive to a core playing this role. This paper presents a new implementation of optimistic semaphores that avoid performing expensive system calls in an uncontended scenario. The implementation is straightforward and somewhat unorthodox: a semaphore is based on a data structure and a lock that are shared between user space and kernel space. This study aims at evaluating if such an approach is viable. In addition, the implementation includes a non-deterministic choice operation over a collection of semaphores, altsems. This novel operation facilitates the creation of higher-level communication mechanisms, such as sockets and channels. To support this claim, we implemented a new kind of buffered communication channels named tubes, tailored for communicating processes running on different (heterogeneous) cores. The paper describes the implementation of the semaphores and the tubes, a comparative analysis of optimistic and non-optimistic semaphores on Nix, and a comparative analysis of tubes and other kinds of communication channels that are available on the Nix operating system. Copyright © 2014 John Wiley & Sons, Ltd.
ZX: A network file system for high-latency networks
(Wiley, 2018) Ballesteros, Francisco J.; Guardiola Múzquiz, Gorka; Soriano-Salvador, Enrique
Using a central file server is good for interactive access to files, because of the coherency implied by a centralized design. In fact, within local area networks, this is a common case. However, distributed environments in use today may exhibit round-trip times on the order of 50 or 100 ms. This is a problem for interactive file access to a central file server because of the resulting access times. Although aggressive caching and loosely synchronized replicas may be used for distributed file access, there are cases where the better coherency provided by a central server is still desirable. In this paper, we present ZX, a distributed file system and protocol designed with latency in mind. It can use caching, but it does not require caching or batching to address latency issues. ZX relies on a novel channel-based file system interface. It includes find requests and leverages streaming requests to work well under high-latency conditions. Unlike other protocols designed for distributed access to a central server, ZX tolerates round-trip times on the order of 50 or 100 ms to access a central file server for interactive usage such as compiling shared sources, running binaries, editing documents, and other similar workloads. It can be used on UNIX using a FUSE adaptor while permitting native ZX speakers to run faster.