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\title{Real-Time CORBA performance on Linux-RT\_PREEMPT}
\subtitle{9th Real-time Linux Conference Linz - Austria}
\author{Manuel Traut}
\institute{Linutronix GmbH}
%\logo{\includegraphics[width=\textwidth]{img/linutronix.jpg}}

\begin{document}

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\begin{frame}
        \tableofcontents
\end{frame}

\section{Introduction}
\subsection{Industrial automation}

\begin{frame}
\frametitle{State-of-the-art}
\begin{block}{Communication}
\begin{itemize}
\item broad variety of industrial fieldbusses
\begin{itemize}
\item CAN
\item Interbus
\item Profibus
\item \dots
\end{itemize}
\item ethernet gains popularity
\begin{itemize}
\item EtherCAT
\item profiNET
\item DeviceNet
\item \dots
\end{itemize}
\end{itemize}
\end{block}
\end{frame}

\begin{frame}
\frametitle{State-of-the-art}
\begin{block}{Controls}
\begin{itemize}
\item PLCs
\begin{itemize}
\item Siemens Simatic, \dots
\item Rockwell PLC-5, \dots
\item \dots
\end{itemize}
\item PC-based controls with real-time operating systems are gaining popularity
\begin{itemize}
\item from the IT world known interfaces (USB, Ethernet, \dots)
\item specialized software for machine control
\end{itemize}
\end{itemize}
\end{block}
\end{frame}

\begin{frame}
\frametitle{PC-based controls and ethernet communications}
allow to use IT middleware solutions in automation
\begin{block}{Advantages of middleware}
\begin{itemize}
\item flexible reusability of software modules
\item ease of maintenance
\item fast development cycles
\item abstraction (operating system, programming language)
\item often repeated complex tasks can be done in middleware
\begin{itemize}
\item connection handling
\item object alocation
\item quality of services
\end{itemize}
\end{itemize}
\end{block}
\end{frame}

\begin{frame}
\frametitle{Contemplated configuration}
\begin{block}{Linux 2.6 with RT\_PREEMPT}
\begin{itemize}
\item successive vanilla integration
\item real-time in userspace
\item available for most recently used architectures
\begin{itemize}
\item x86 and x86\_64
\item arm
\item mips
\item powerpc
\end{itemize}
\end{itemize}
\end{block}
\end{frame}

\begin{frame}
\frametitle{Contemplated configuration}
\begin{block}{TAO, real-time CORBA distribution}
\begin{itemize}
\item c++ implementation
\item based on ACE (operating system independent)
\item RTCORBA specification implemented
\item open source software
\item commercial support
\item widely used
\end{itemize}
\end{block}
\end{frame}

\subsection{CORBA}

\begin{frame}
\frametitle{Common Object Request Broker Architecture}
\begin{block}{abstracts}
\begin{itemize}
\item operating systems
\item programming language
\item transport protocol
\end{itemize}
\end{block}
\end{frame}

\begin{frame}
\frametitle{Functional principle}
\begin{center}
\includegraphics[height=0.8\textheight]{img/orb.jpg}
\end{center}
\end{frame}

\begin{frame}
\frametitle{Functional principle}
\begin{block}{CORBA Services}
\begin{itemize}
\item Naming Service
\begin{itemize}
\item Task A: bind object ior with name to Naming Service
\item Task B: resolve object ior by name from Naming Service
\end{itemize}
\item Messaging Service
\begin{itemize}
\item Task A: send messages to Messaging Service (Publisher)
\item Task B: subscribe for messages, e.g. filtered by topic, from the Messaging Service
\end{itemize}
\end{itemize}
\end{block}
\end{frame}

\begin{frame}
\frametitle{Real-time CORBA extensions}
\begin{center}
\includegraphics[height=0.7\textheight]{img/rtcorbaext.jpg}
\end{center}
\begin{raggedright}
%\scriptsize OMG Real-time CORBA speccification
\end{raggedright}
\end{frame}

\subsection{ACE/TAO framework}

\begin{frame}
\frametitle{Software architecture}
\begin{center}
\includegraphics[height=0.7\textheight]{./img/ace.jpg}
\end{center}
\begin{raggedright}
\scriptsize http://cs.wustl.edu/schmidt/ACE
\end{raggedright}
\end{frame}

\section{Performance measurements}

\begin{frame}
\begin{quote}
One of the problems of taking things apart and seeing how they work, 
supposing you're trying to find out how a cat works, 
you take that cat apart to see how it works, what you've got in your hands is a non-working cat. 

The cat wasn't a sort of clunky mechanism that was susceptible to our available tools of analysis.
\end{quote}
\begin{raggedright}
\scriptsize Douglas Adams, Hitchhiker's Guide tot the Galaxy
\end{raggedright}
\end{frame}

\begin{frame}
\frametitle{Measurement environment}
\begin{center}
\includegraphics[height=0.8\textheight]{img/versuch4.jpg}
\end{center}
\end{frame}

\subsection{Remote Procedure Calls}

\begin{frame}
\frametitle{Sequence diagram}
\begin{center}
\includegraphics[width=\textwidth]{img/sequenzV1.jpg}
\end{center}
\end{frame}

\begin{frame}
\frametitle{Latency histogram}
\begin{center}
\includegraphics[height=0.7\textheight]{img/v1Last.jpg}
\end{center}
\begin{raggedright}
\scriptsize RT\_PREEMPT, with system load
\end{raggedright}
\end{frame}

\begin{frame}
\frametitle{Latency histogram}
\begin{center}
\includegraphics[height=0.7\textheight]{img/vanilla-ohne-last.jpg}
\end{center}
\begin{raggedright}
\scriptsize vanilla, without system load
\end{raggedright}
\end{frame}

\begin{frame}
\frametitle{Latency histogram}
\begin{center}
\includegraphics[height=0.7\textheight]{img/vanilla-mit-last.jpg}
\end{center}
\begin{raggedright}
\scriptsize vanilla, with system load
\end{raggedright}
\end{frame}

\begin{frame}
\frametitle{Latency histogram}
\begin{center}
\includegraphics[height=0.7\textheight]{img/v3Last.jpg}
\end{center}
\begin{raggedright}
\scriptsize RT\_PREEMPT, two prioizations, with system load
\end{raggedright}
\end{frame}

\begin{frame}
\frametitle{Latency histogram}
\begin{center}
\includegraphics[height=0.7\textheight]{img/v4plot.jpg}
\end{center}
\begin{raggedright}
\scriptsize RT\_PREEMPT, dependency between data package size and latency
\end{raggedright}
\end{frame}

\subsection{Event-channel}

\begin{frame}
\frametitle{Sequence diagram}
\begin{center}
\includegraphics[width=\textwidth]{img/sequenzV2.jpg}
\end{center}
\end{frame}

\begin{frame}
\frametitle{Latency histogram}
\begin{center}
\includegraphics[height=0.7\textheight]{img/v2Last.jpg}
\end{center}
\begin{raggedright}
\scriptsize RT\_PREEMPT, TAO RT Event-Channel, with system load
\end{raggedright}
\end{frame}

\section{Status: ACE/TAO on RT\_PREEMPT}

\subsection{Needed operating system functionalities}

\begin{frame}
\frametitle{End to end real-time guarantee}
\begin{block}{Real-time scheduling}
\begin{itemize}
\item deterministic scheduling latency
\item RTCORBA expects priorization based scheduling
\item interrupts shouldn't destroy deterministic scheduling
\end{itemize}
\end{block}
\pause
\begin{block}{Real-time I/O}
\begin{itemize}
\item hardware device priorization is required
\begin{itemize}
\item IO hardware, used for machine control (measurements)
\item Network device, used for RTCORBA communication
\end{itemize}
\end{itemize}
\end{block}
\end{frame}

\begin{frame}
\frametitle{End to end real-time guarantee}
\begin{block}{real-time networking}
\begin{itemize}
\item measurements were made with IIOP using diffserv priorization in the IP header
\item diffserv has to be supported by all attendees
\begin{itemize}
\item operating systems network stack
\item nic driver
\item switches
\end{itemize}
\item in most cases real-time is lost, if the packages has to pass routers
\end{itemize}
\end{block}
\end{frame}

\begin{frame}
\frametitle{Used RT\_PREEMPT features}
\begin{block}{Scheduling}
\begin{itemize}
\item PI-Mutexes
\item priorization based scheduler (same as in vanilla)
\item interrupt handling in kernel threads
\end{itemize}
\end{block}
\pause
\begin{block}{Real-time IO}
\begin{itemize}
\item priorization of interrupts (kernel threads)
\item problems with interrupt sharing
\end{itemize}
\end{block}
\end{frame}

\begin{frame}
\frametitle{Used RT\_PREEMPT features}
\begin{block}{Real-time networking}
\begin{itemize}
\item priorization of network interrupts
\item problems with different priorized nics:
\begin{itemize}
\item all ethernet traffic is handled in two common softirqs
\end{itemize}
\item kernel community has already discussed solutions
\end{itemize}
\end{block}
\end{frame}

\section{Conclusion}

\begin{frame}
\begin{block}{Promising solution}
\begin{itemize}
\item acceptable measurement results
\item improvements can be made in the networking layer
\end{itemize}
\end{block}
\begin{block}{not only automation industry}
also other application areas, eg.
\begin{itemize}
\item telecommunication
\item stock market
\item \dots
\end{itemize}
need deterministic networking.
\end{block}
\end{frame}

\begin{frame}
\frametitle{ACE/TAO and RT\_PREEMPT enabled Linux}
\begin{itemize}
\item is already a useful and solid environment
\item further improvements in foreseeable future
\end{itemize}
\end{frame}

\begin{frame}
\frametitle{Thank you for your attention}
\begin{block}{Contact}
\vskip3pt
Linutronix GmbH\\
Manuel Traut\\
\vskip3pt
Auf dem Berg 3\\
88690 Uhldingen\\
Germany\\
\vskip3pt
eMail manuel.traut@linutronix.de\\
fon +49 7556 919 891
\end{block}
\end{frame}


\end{document}
