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Linux for High Performance and Real-Time Computing on

SMP Systems

∗

Dominique RAGOT, Yulen SADOURNY

Thales, Colombes, France

{dominique.ragot,yulen.sadourny}@fr.thalesgroup.com

Denis FOUEILLASSAR, Philippe COUVEE

Bull, Grenoble, France

{denis.foueillassar,philippe.couvee}@bull.net

L´eonard SIBILLE

CEA List, Fontenay aux Roses, France

leonard.sibille@cea.fr

Jean-Luc DEKEYSER, Philippe MARQUET, Eric PIEL, Julien SOULA

LIFL, University of Lille, France

{jean-luc.dekeyser,philippe.marquet,eric.piel,julien.soula}@liﬂ.fr

Hugo KOHMANN

Dolphin Interconnect, Oslo, Norway

hugo@dolphinics.no

Alexis BERLEMONT

Openwide, Paris, France

alexis.berlemont@openwide.fr

Abstract

Applications that require a combination of high-performance computing capabilities and real-time

behavior, although pervasive (simulation, medicine, training, multimedia communications), often rely on

speciﬁc hardware and software components that make them high performance but expensive, and quite

diﬃcult to develop, validate and moreover upgrade. The increasing performance of COTS and the volume

of software developed for these applications lead to the consideration of incremental development schemes

in addition to sole performance. In the ITEA Hyades project, industrial companies, research centres

and academic departments, propose a complete set of software technologies aimed at adding real-time

capabilities to multi-processor systems, with a strong commitment to standards. In this paper we present

the application requirements with respect to real-time, the architectural model proposed, as well as the

reasons for using the Linux operating system. Then, we introduce software components that have been

selected to provide real-time needs, among which are Adeos and ARTiS, and their expected contribution to

global performance. Finally we provide performance measurements for these elements.

∗

This work has been done in the scope of the Hyades project, ITEA 01010

1 Introduction

The integration of digital systems in many aspects

of life is now a reality of every day. In many ﬁelds of

activity: oﬃce, leisure, health, security, transporta-

tion, we are indeed communicating with computers,

without having to know how this communication is

managed. Terminals, computers and networks have

simply to bring together the required services to the

end-users in a seamless fashion. This integration re-

quires infrastructure components that must deliver

both functionality and performance. For a majority

of systems, performance relates to throughput, but

for a growing number of domains (video and audio

contents delivery, virtual reality, manufacturing pro-

cess control, sensor fusion) performance relates to

timely execution. Such applications have usually re-

quired non-standard and costly hardware and soft-

ware solutions. Their speciﬁcity had been for years

the justiﬁcation for the use of speciﬁc technology at

all levels: specialized DSP processors, specialized

operating systems lacking the support of standard

APIs and requiring custom applications, and also

specialised cluster interconnects.

Moreover the diﬀusion and utilization of paral-

lel distributed systems based on COTS (components

oﬀ the shelf) technology has widely increased in last

years. Today, using COTS, it is possible to build

up powerful clusters not only for number crunch-

ing but also for highly parallel commercial applica-

tions. Many computer manufacturers have adopted

this approach, and now high performance comput-

ing systems are available at a price very low with

respect to one decade ago.

Real-time capabilities for these systems have not

reached a comparable level of maturity due to lim-

ited market size. In order to evaluate what level of

performance could be reached, a multidisciplinary

team [1] has designed and developed real-time ex-

tensions for parallel systems whose requirements,

contents, and results are exposed in the following

chapters.

2 Applications requirements

For complex applications, real-time constraints are

expressed at several levels of interaction. When

there is close man-system interactions (e.g in virtual

reality applications), the constraints are expressed in

relation to perception. On the other hand, for data

acquisition systems, the receiver/emitter must not

cause data to be lost due to lack of temporal control

over some asynchronous events.

Because they are complex, these applications

also make large usage of components that are not in

dealing at all with real-time issues. For instance all

back end processing such as classiﬁcation, database

access, global conﬁguration and monitoring, typi-

cally rely on several legacy or third-party middle-

ware and tools components. The underlying soft-

ware architecture has to provide capabilities to inte-

grate these components in a seamless fashion.

In order to assess the versatility of the proposed

architecture for this class of applications, we have

chosen the following two cases:

2.1 Virtual Reality

One application of the real-time kernel is the simu-

lation of industrial parts in virtual reality. Industri-

alists currently use real-life mock-ups for assembly

testing. This process takes a large amount of time

and money. Virtual reality makes such testing eas-

ier and cheaper. Once converted into appropriate

3D computer models, industrial parts are integrated

into a simulation framework which computes dy-

namics and collisions between parts. In addition,

the simulation is connected to a force-feedback de-

vice which enables the user to feel collision forces,

as shown on ﬁgure 1.

This device, however, must be fed with force

data at a very high rate (1kHz, typically). Failure

to respect this rate results in jitter, and eventually

makes the simulation crash. Today, the simulated

3D models can only consist of a few thousand poly-

gons, because of this rate constraint. A SMP ma-

chine enables developers to isolate and make par-

allel the dynamics and collision processes, which

should give dramatically better performance. The

real-time patch will ensure the real-time constraint

is enforced. All this should result in more detailed

models, and better testing accuracy.

FIGURE 1: Linking a haptic device to a 3D sim-

ulation

2.2 Video proxy

The video proxy is an application located some-

where in the network between the server and the

end-user. It is typically placed at the edge of a net-

work, where the available bandwidth or the security

requirements change (see ﬁgure 2). The purpose of

a video proxy is mainly to adapt the video streams

going through it, depending on the users’ character-

istics at the end of the delivery chain.

FIGURE 2: Proxy in video distribution

Description and Functionality The processing of

a video stream during its transmission requires spe-

cialised modules, due to the high data rates in-

volved. A video proxy allows to perform user au-

thentication as well as ﬁltering and logging on any

traﬃc that traverses the proxy server. But its main

and most heavy task consists of pure video-related

processing, speciﬁcally at the edge of heterogeneous

networks:

• Transcoding of video content, i.e. dynamic

adaptation to ensure a certain quality-of-

service. Some content formats are designed to

optimise scalability, such as Motion JPEG 2000

or the upcoming MPEG-SVC, thus allowing to

transcode streams without going through the

entire encoding chain.

• Scalable encryption to ensure the conﬁdential-

ity of critical data. This kind of encryption

selects the byte chunks to cipher and allows

to keep the structure of the video content in-

tact. One of the main advantages of these tech-

niques is to allow the transcoding of ciphered

streams.

A generic video proxy can implement some traf-

ﬁc control, but does not contain any ﬁrewalling ca-

pability. In this way, it can be deployed behind a

traditional ﬁrewall platform. Therefore, a typical

use on a private network area can be the follow-

ing: a main ﬁrewall accepting inbound traﬃc, de-

termines which application is being targeted, and

then hands oﬀ the traﬃc to an appropriate proxy

server, e.g. videos to the video proxy. This way,

such a dedicated proxy can be used to decrease the

work load on the ﬁrewall and to perform more spe-

cialised processing that otherwise may be diﬃcult

or even impossible to perform on the ﬁrewall itself.

Application constraints Today, the two main limi-

tations for video proxy modules are the low ﬂexibil-

ity of content formats, although some standards are

emerging, and the computing power of networks

nodes, which have high performance for basic pro-

cesses such as routing but are not optimised for more

complex computation like transcoding.

The critical parameters for the machine when

the proxy runs are the CPU-load and the achieved

quality of service for the clients behind. The appli-

cation performs a continuous, on-stream processing

and must do the work in real-time, so that the video

quality, resolution and frame-rate remain constant

on the end-users’ players.

3 The proposed architecture

Multiprocessor systems are well suited to provide

the required processing power for such applications

as well as a choice of operating systems and mid-

dleware tools, at least when excluding real-time is-

sues. Including real-time capabilities directly usable

by application designers dramatically reduces this

choice and oﬀers a limited set of solutions:

1. pure RTOS-based solutions are usually quite

limited in terms of middleware and tools sup-

ported, and only a very few of them have sup-

port for multiprocessor systems. The appli-

cation developer has usually no choice but to

partition the number of processors available

in two sets: one with RT capabilities running a

RTOS, and the other running a GPOS with all

applications. Communications within and be-

tween sets are done using MPI-like primitives.

Besides having to statically deﬁne resources

for RT and non-RT parts of the application,

this solution requires that all communication

software be developed in a way that is highly

dependent on the underlying machine archi-

tecture.

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zyzhang3

2015-01-01

好文章，感谢楼主，学习了！

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