elc16.tex

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\title[Lessons from Ion]{Lessons from Ion}

\author{Laura Abbott}
\institute[Red Hat]
{
\textit{labbott@redhat.com}
\\
\textit{labbott@fedoraproject.org}
\\
\textit{laura@labbott.name}
}
\date{April 6, 2016}

\begin{document}

\begin{frame}
\titlepage
\end{frame}

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%	PRESENTATION SLIDES
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\begin{frame}
\frametitle{Which Ion?}
\begin{itemize}
\item Not the tiling window manager
\item Not the cell phone
\item Not the latest framework Google released
\item Yes, the framework in drivers/staging/android/ion
\end{itemize}
\end{frame}

\begin{frame}
\frametitle{Who Am I?}
\begin{itemize}
\item Not the original Ion author
\item Used to crash cell phones
\item Currently crash Fedora
\item "Maintainer" of Ion
\end{itemize}
\end{frame}

\begin{frame}
\frametitle{Why?}
\Huge{\centerline{Why am I talking about this?}}
\end{frame}

\begin{frame}
\frametitle{Ion introduction}
\begin{itemize}
\item Need a way to manage memory pools
\item Everyone has a pet framework
\item Ion is consolidated framework
\item Sharing, allocation, mapping
\item Lesson: consolidation is good
\end{itemize}
\end{frame}

\begin{frame}
\frametitle{Ion concepts: Heap}
\begin{itemize}
\item Single type of memory
\item Specific carveout region, buddy pages, CMA region etc.
\item bitmask of IDs for allocation
\item allows for fallback depending on system configuration
\end{itemize}
\end{frame}

\begin{frame}[fragile]
\frametitle{Ion concepts: Heap}
\begin{verbatim}
struct ion_allocation_data {
        size_t len;
        size_t align;
        unsigned int heap_id_mask;
        unsigned int flags;
        ion_user_handle_t handle;
};

#define ION_IOC_ALLOC           _IOWR(ION_IOC_MAGIC, 0, \
                               struct ion_allocation_data)
\end{verbatim}
\end{frame}


\begin{frame}
\frametitle{Heap example: System X}
\begin{itemize}
\item Some mixture of heaps
\item Some IOMMUs, some not
\item Heaps A and B
\item \begin{itemize}
\item Heap A - carveout highest priority
\item Heap B - buddy pages
\end{itemize}
\end{itemize}
\end{frame}

\begin{frame}
\frametitle{Heap example: System Y}
\begin{itemize}
\item Fun new hardware block
\item Requirement: use the memory that was carved out for Heap A
\item Existing heap ID or new heap ID?
\end{itemize}
\end{frame}

\begin{frame}
\frametitle{Heap example: System Z}
\begin{itemize}
\item Beautiful looking system
\item Beautiful looking hardware errata to work around
\item One errata time n systems = wait where did the bits go?
\end{itemize}
\end{frame}

\begin{frame}
\frametitle{Heap conclusion}
Lesson: Think about your ABIs. \\
Please make them discoverable
\end{frame}


\begin{frame}
\frametitle{Ion concept: Client}
\begin{itemize}
\item Notion of 'ownership'
\item open("/dev/ion") and kernel APIs
\item Lesson: existing models are there for a reason
\end{itemize}
\end{frame}

\begin{frame}
\frametitle{Sharing}
\begin{itemize}
\item fds for sharing
\item dma\_buf is the generic version
\item Lesson: Take what works!
\end{itemize}
\end{frame}

\begin{frame}
\frametitle{Ion concept: buffer/handle}
\begin{itemize}
\item buffer represents a specific allocation
\item handle reference per client
\item Reference counting of everything! \\
\includegraphics[scale=0.5]{ion_handle.png}
\end{itemize}
\end{frame}

\begin{frame}
\frametitle{Writing correct code is hard}
\begin{itemize}
\item Reference counting is hard to get right for everyone!
\item Still finding race conditions
\item Users need to be able to debug their code (I don't want to debug your code)
\end{itemize}
\end{frame}

\begin{frame}
\frametitle{What did we learn here?}
Lesson: Concurrency is hard \\
Lesson: Think about debugging in the beginning
\end{frame}

\begin{frame}
\frametitle{So}
Do we still need Ion? Does anyone care?
\end{frame}

\begin{frame}
\frametitle{Yes and...}
\begin{itemize}
\item Android?
\item Userspace allocation seems popular
\item Generic allocation framework?
\item Devicetree?
\item Lesson: mainlining takes work. Why are you doing it?
\end{itemize}
\end{frame}

\begin{frame}
\frametitle{Summary}
\begin{itemize}
\item The kernel has missing pieces, code but think about your goals
\item ABIs are hard
\item Concurrency is hard
\item Debugging is hard
\item Think twice before creating your own model, expand instead
\item Do you care about getting it in mainline?
\end{itemize}
\end{frame}

\begin{frame}
\frametitle{Questions?}
\Huge{\centerline{Questions?}}
\end{frame}

\end{document}