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\renewcommand{\FIGREP}{src/cluster_architecture/figures}
\section{Cluster Architecture}
\label{sec:cluster_architecture}
\intersec{helvetios}
\begin{frame}[t]
\frametitle{Cluster Architecture}
\framesubtitle{}
\begin{itemize}
\item The goal of this section is to understand what's under the cluster's
hood
\item In order to take full advantage of your computer, you have to
understand how it works, what are the limits, etc.
\item We'll go from the cluster level down to the core level
\end{itemize}
\addimage[width=7cm]{\FIGREP/summit}{5.5cm}{0.5cm}
\end{frame}
\subsection{Cluster as a whole}
\label{sec:cluster}
\begin{frame}
\frametitle{Cluster Architecture}
\framesubtitle{General presentation}
\begin{minipage}{0.5\linewidth}
\begin{itemize}
\item An HPC cluster is composed of
\begin{itemize}
\item Login node(s)
\item Compute nodes
\item Storage system
\item High performance interconnect
\end{itemize}
\item Using a scheduler, the simulations are sent to the compute nodes
which perform the computations
\item The simulation data is written on the storage systems. At SCITAS:
\begin{itemize}
\item \code{/home}: store source files, input data, small files
\item \code{/work}: collaboration space for a group
\item \code{/scratch}: temporary huge result files
\end{itemize}
Please, note that only \cmd{/home} and \cmd{/work} have backups!
\cmd{/scratch} data can be erased at any moment!
\end{itemize}
\end{minipage}
\addimage[width=6cm]{\FIGREP/abstract_architecture}{9.5cm}{1.5cm}
\end{frame}
\note{
\begin{itemize}
\item The users connect to the login node
\item Backups on \code{/work} are paying
\end{itemize}
}
\begin{frame}[t]
\frametitle{Cluster Architecture}
\framesubtitle{A few numbers}
\textbf{Let's go back to Summit}
\begin{itemize}
\item Second most powerful HPC cluster in the world according to the
\href{https://www.top500.org/lists/top500/list/2021/06/}{Top500 June
2021 list}
\item It is composed of \SI{4608}{} compute nodes
\item Power consumption of \SI{10096.00}{\kilo\watt}
% Consommation annuelle par habitant en Suisse ~6956kWh
\item Equivalent consumption as a city with $\sim$\SI{13000}{} inhabitants
% Prix du kWh a Lausanne ~20 centimes
\item In Lausanne, running Summit would cost $\sim$\SI{50000}{\chf\per\day} only for electricity!
\end{itemize}
\addimage[width=5cm]{\FIGREP/summit}{5.5cm}{1.0cm}
\end{frame}
\subsection{The compute node}
\label{sec:node}
\begin{frame}[t]
\frametitle{Cluster Architecture}
\framesubtitle{Let's dive into a compute node!}
\begin{itemize}
\item The compute node is the basic building bloc of a cluster
\item It is composed of one or more CPU with RAM (memory) and eventually one
or more accelerator, e.g. GPUs
\item All the nodes are connected together with an interconnect
\end{itemize}
\addimage[width=4.5cm]{\FIGREP/node_architecture}{5.75cm}{1.0cm}
\end{frame}
\note{
\begin{itemize}
\item A compute node is like a personal computer on steroid
\end{itemize}
}
\subsection{The CPU}
\label{sec:cpu}
\begin{frame}[t]
\frametitle{Cluster Architecture}
\framesubtitle{Central processing unit}
\begin{itemize}
\item The CPU is the ``brain'' of the node
\item CPUs work in clock cycles; they are the ``heart beat'' of the CPU
\item It is composed of cores and different levels of memories called caches
\item There are usually three levels of cache called L1, L2, and L3
\end{itemize}
\vspace{0.8cm}
\begin{table}
\hspace{5cm}
\scriptsize
\begin{tabular}{@{}llll@{}}
\toprule
\textbf{Event} & \textbf{Latency} & \textbf{Scaled} & \textbf{Capacity} \\
\midrule
1 CPU cycle & 0.1\,ns & 1 s & -- \\
L1 cache access & 1\,ns & 10\,s & kB \\
L2 cache access & 1\,ns & 10\,s & MB \\
L3 cache access & 10\,ns & 1\,min & MB \\
RAM access & 100\,ns & 10\,min & GB \\
Solid-state disk access & 100\,$\mu$s & 10 days & TB \\
Hard-disk drive access& 1--10\,ms & 1--12 months & TB \\
\bottomrule
\end{tabular}
\end{table}
\addimage[width=4cm]{\FIGREP/cpu_architecture}{3cm}{1.5cm}
\end{frame}
\note{
\begin{itemize}
\item Caches are extremely fast memories that are used to hide the latency
of other memories (RAM, hard drive, etc.)
\item However, they are usually quite small compared to e.g. RAM, hard drive
\item L1 is the closest to the core, followed by L2 and L3
\item Some cache levels are private to a core, e.g. here L1 and L2
\end{itemize}
}
\begin{frame}[t]
\frametitle{Cluster Architecture}
\framesubtitle{Summary of SCITAS' clusters}
\textcolor{red}{I would like to put a summary of SCITAS' clusters, but I would
need to introduce also the concept of \si{\flops}...}
\vfill
\begin{minipage}{0.32\linewidth}
\begin{center}
\textbf{Fidis}
\end{center}
\end{minipage}
\hfill
\begin{minipage}{0.32\linewidth}
\begin{center}
\textbf{Helvetios}
\end{center}
\end{minipage}
\hfill
\begin{minipage}{0.32\linewidth}
\begin{center}
\textbf{Izar}
\end{center}
\end{minipage}
\end{frame}
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