A Hardware Time Manager Implementation for the Xenomai Real-Time Kernel of Embedded Linux

Nowadays, the use of embedded operating systems in different embedded projects is subject to a tremendous growth. Embedded Linux is becoming one of those most popular EOSs due to its modularity, efficiency, reliability, and cost. One way to make it hard real-time is to include a real-time kernel like Xenomai. One of the key characteristics of a Real-Time Operating System (RTOS) is its ability to meet execution time deadlines deterministically. So, the more precise and flexible the time management can be, the better it can handle efficiently the determinism for different embedded applications. RTOS time precision is characterized by a specific periodic interrupt service controlled by a software time manager. The smaller the period of the interrupt, the better the precision of the RTOS, the more it overloads the CPU, and though reduces the overall efficiency of the RTOS. In this paper, we propose to drastically reduce these overheads by migrating the time management service of Xenomai into a configurable hardware component to relieve the CPU. The hardware component is implemented in a Field Programmable Gate Array coupled to the CPU. This work was achieved in a Master degree project where students could apprehend many fields of embedded systems: RTOS programming, hardware design, performance evaluation, etc.Comment: Embed With Linux (EWiLi) workshop, Lorient : France (2012

On Benchmarking Embedded Linux Flash File Systems

Due to its attractive characteristics in terms of performance, weight and power consumption, NAND flash memory became the main non volatile memory (NVM) in embedded systems. Those NVMs also present some specific characteristics/constraints: good but asymmetric I/O performance, limited lifetime, write/erase granularity asymmetry, etc. Those peculiarities are either managed in hardware for flash disks (SSDs, SD cards, USB sticks, etc.) or in software for raw embedded flash chips. When managed in software, flash algorithms and structures are implemented in a specific flash file system (FFS). In this paper, we present a performance study of the most widely used FFSs in embedded Linux: JFFS2, UBIFS,and YAFFS. We show some very particular behaviors and large performance disparities for tested FFS operations such as mounting, copying, and searching file trees, compression, etc.Comment: Embed With Linux, Lorient : France (2012

Toward a Unified Performance and Power Consumption NAND Flash Memory Model of Embedded and Solid State Secondary Storage Systems

This paper presents a set of models dedicated to describe a flash storage subsystem structure, functions, performance and power consumption behaviors. These models cover a large range of today's NAND flash memory applications. They are designed to be implemented in simulation tools allowing to estimate and compare performance and power consumption of I/O requests on flash memory based storage systems. Such tools can also help in designing and validating new flash storage systems and management mechanisms. This work is integrated in a global project aiming to build a framework simulating complex flash storage hierarchies for performance and power consumption analysis. This tool will be highly configurable and modular with various levels of usage complexity according to the required aim: from a software user point of view for simulating storage systems, to a developer point of view for designing, testing and validating new flash storage management systems

A Cache Management Strategy to Replace Wear Leveling Techniques for Embedded Flash Memory

Prices of NAND flash memories are falling drastically due to market growth and fabrication process mastering while research efforts from a technological point of view in terms of endurance and density are very active. NAND flash memories are becoming the most important storage media in mobile computing and tend to be less confined to this area. The major constraint of such a technology is the limited number of possible erase operations per block which tend to quickly provoke memory wear out. To cope with this issue, state-of-the-art solutions implement wear leveling policies to level the wear out of the memory and so increase its lifetime. These policies are integrated into the Flash Translation Layer (FTL) and greatly contribute in decreasing the write performance. In this paper, we propose to reduce the flash memory wear out problem and improve its performance by absorbing the erase operations throughout a dual cache system replacing FTL wear leveling and garbage collection services. We justify this idea by proposing a first performance evaluation of an exclusively cache based system for embedded flash memories. Unlike wear leveling schemes, the proposed cache solution reduces the total number of erase operations reported on the media by absorbing them in the cache for workloads expressing a minimal global sequential rate.Comment: Ce papier a obtenu le "Best Paper Award" dans le "Computer System track" nombre de page: 8; International Symposium on Performance Evaluation of Computer & Telecommunication Systems, La Haye : Netherlands (2011

FFSMark : Un Benchmark pour Systèmes de Fichiers Dédiés aux Mémoires Flash

International audienceLa mémoire flash de type NAND est le principal média de stockage dans l'embarqué. L'un des moyens pour intégrer cette mémoire dans les systèmes informatiques est d'utiliser des systèmes de fichiers dédiés aux mémoires flash (Flash File Systems, FFS). Dans ce domaine, les benchmarks sont des programmes permettant de réaliser des études de performances et de comparer différents systèmes entre eux. Nous montrons dans cet article qu'un benchmark pour FFS doit prendre en compte les caractéristiques spécifiques des mémoires flash, d'une part dans son comportement, et d'autre part en ce qui concerne les métriques de performances disponibles en sortie. Dans ce contexte, nous proposons FFSMark, un benchmark ciblant les FFS, sensible aux spécificités des mémoires flash. FFSMark est dédié à être exécuté sous Linux, un système d'exploitation supportant les FFS les plus populaires. Nous présentons également une étude de cas, utilisant FFSMark pour comparer les performances des FFS JFFS2, YAFFS2 et UBIFS sur une plate-forme embarquée

Evaluation of the Performance/Energy Overhead in DSP Video Decoding and its Implications

Video decoding is considered as one of the most compute and energy intensive application in energy constrained mobile devices. Some specific processing units, such as DSPs, are added to those devices in order to optimize the performance and the energy consumption. However, in DSP video decoding, the inter-processor communication overhead may have a considerable impact on the performance and the energy consumption. In this paper, we propose to evaluate this overhead and analyse its impact on the performance and the energy consumption as compared to the GPP decoding. Our work revealed that the GPP can be the best choice in many cases due to the a significant overhead in DSP decoding which may represents 30% of the total decoding energy

A Multilevel I/O Tracer for Timing and Performance Analysis of Storage Systems in IaaS Cloud

REACTION 2014. 3rd International Workshop on Real-time and Distributed Computing in Emerging Applications. Rome, Italy. December 2nd, 2014.Data centers are more and more relying on hybrid storage systems consisting of flash memory based storage devices and traditional hard disk drives. Optimal data placement in such hybrid storage systems is a very important issue in the domain of cloud computing and virtualization. This is specially the case when users need that storage systems enforce Quality of Service requirements on I/Os performed, for example for multimedia applications. To characterize Virtual Machine (VM) I/O workload properties such as timing predictability or throughput, monitor-ing services are necessary on such new architectures. This article presents a multilevel I/O tracer for virtual machines that relies on and complement different state-of-the-art tools. It produces I/O traces at different levels of the Linux I/O software stack. The I/O tracer gives an exhaustive information that allows administrators to precisely characterize virtual machine I/O behavior in terms of percentage of read/write I/Os, percentage of random/sequential, I/O request inter-arrival time, etc. This tool is the first piece towards a middleware whose purpose is to meet user QoS requirements thanks to optimal data placement and migration policies in a hybrid storage system in the context of an IaaS Cloud.This work has been funded by the French government through the National Research Agency (ANR) Investment referenced ANR-A0-AIRT-07Publicad

Flashmon : un outil de trace pour les accès à la mémoire flash NAND

nombre de pages: 6International audienceLes mémoires flash deviennent une technologie incontournable dans le domaine de l'embarqué. Leur succès est dû, essentiellement, à leur taille, leur légèreté, leur résistance au choc et leur faible consommation énergétique. Concernant les performances, l'avantage majeur que représentent ces mémoires, comparées aux disques durs, est leur performance homogène en lecture (séquentielle ou aléatoire). En revanche, pour les écritures, elles souffrent d'une durée de vie réduite à cause du nombre très limité d'effacements pouvant être appliqué à leurs cellules. L'un des axes de recherche le plus important consiste à établir des politiques permettant de niveler l'usure sur toute la surface afin de maximiser sa durée de vie moyenne. Il apparaît donc très important d'avoir à disposition des outils permettant de tracer les accès à la mémoire flash. Ceci permet, d'une part, lors de la conception, de tester et de valider des solutions mettant en œuvre des mémoires flash, et d'autre part, après implémentation, de surveiller l'usure en cours de fonctionnement. Ce papier présente Flashmon, un outil flexible et configurable, permettant de tracer, en temps réel, les accès à la mémoire flash NAND embarquée. Flashmon a été développé dans le cadre d'un projet étudiant de Master 2eannée et sera proposé pour intégration dans les noyaux Linux

Performance Evaluation of Flash File Systems

Today, flash memory are strongly used in the embedded system domain. NAND flash memories are the building block of main secondary storage systems. Such memories present many benefits in terms of data density, I/O performance, shock resistance and power consumption. Nevertheless, flash does not come without constraints: the write / erase granularity asymmetry and the limited lifetime bring the need for specific management. This can be done through the operating system using dedicated Flash File Systems (FFSs). In this document, we present general concepts about FFSs, and implementations example that are JFFS2, YAFFS2 and UBIFS, the most commonly used flash file systems. Then we give performance evaluation results for these FFSs.Comment: Colloque du GDR SoC-SiP, Paris : France (2012