printk: add printk slides from elce2018

Signed-off-by: John Ogness <john.ogness@linutronix.de>

1 files changed, 123 insertions, 0 deletions

diff --git a/misc/pres_printk_en.tex b/misc/pres_printk_en.tex
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+\input{configpres}
+\date{2018-10-25}
+
+\section{printk}
+
+\title{Cleaning Up printk()}
+\author{John Ogness}
+
+\maketitle
+
+\newcommand\verbbf[1]{\textcolor[rgb]{0,0,0}{\textbf{#1}}}
+
+\subsection{printk: Issues}
+
+\begin{frame}[containsverbatim]
+\begin{itemize}
+\item global log buffer protected by \verb|raw_spinlock|
+\begin{itemize}
+\item disables interrupts
+\item not NMI safe
+\item not recursive safe
+\end{itemize}
+\item \verb|printk_safe|
+\begin{itemize}
+\item relies on \verb|irq_work|
+\item bogus timestamps
+\end{itemize}
+\item console drivers
+\begin{itemize}
+\item slow (serial, video, netconsole)
+\item executed by \verb|printk()| caller (possibly atomic)
+\end{itemize}
+\item INFO handled the same as EMERG
+\begin{itemize}
+\item \verb|BUG()| is worth the pain, but ''\verb|USB Video Class driver (1.1.1)|''?
+\end{itemize}
+\item last \verb|printk()| stuck with the bill
+\begin{itemize}
+\item it is not unbounded but it is a big wildcard
+\end{itemize}
+\item \verb|oops_in_progress| and \verb|bust_spinlocks()|
+\begin{itemize}
+\item um, yeah
+\end{itemize}
+\end{itemize}
+\end{frame}
+
+\subsection{printk: Proposal}
+
+\begin{frame}[containsverbatim]
+\begin{itemize}
+\item new static global lockless multi-reader multi-writer ring buffer
+\begin{itemize}
+\item interrupts never disabled
+\item NMI safe
+\item recursive safe
+\item available immediately
+\item obsoletes \verb|printk_safe| (log directly from \textbf{any} context)
+\end{itemize}
+\item grab timestamp as first line of \verb|printk()|
+\begin{itemize}
+\item accurate timestamps
+\end{itemize}
+\item create a single \verb|printk| kthread to handle printing to all consoles
+\begin{itemize}
+\item fully preemptible
+\item console driver pain goes away
+\end{itemize}
+\item introduce a \verb|write_atomic()| operation for consoles
+\begin{itemize}
+\item optional, NMI safe write implementation
+\end{itemize}
+\item introduce the concept of ''emergency messages''
+\begin{itemize}
+\item If a message is flagged for emergency and a console implements \verb|write_atomic()|, print the message for that console \textbf{directly}
+\item We are already sitting on the CPU! Use it!
+\item \verb|write_atomic()| for UART 8250 implemented as an example
+\end{itemize}
+\item add CPU ID to output to flag and sort messages
+\begin{itemize}
+\item simultaneous emergency/non-emergency messages
+\item simultaneous emergency messages
+\end{itemize}
+\end{itemize}
+\end{frame}
+
+\subsection{printk: Proposal: Issues}
+
+\begin{frame}[containsverbatim]
+\begin{itemize}
+\item messages printed out of order
+\begin{itemize}
+\item but timestamps have meaning
+\end{itemize}
+\item \verb|LOG_CONT| not yet implemented
+\begin{itemize}
+\item need to decide how best to implement it
+\end{itemize}
+\item the new ring buffer does not support dynamic resizing
+\begin{itemize}
+\item not looked into yet
+\end{itemize}
+\item vmcore data changes
+\begin{itemize}
+\item userspace ABI changes
+\end{itemize}
+\end{itemize}
+\end{frame}
+
+\subsection{}
+
+\begin{frame}[containsverbatim]
+\frametitle{Questions / Comments}
+Thank you for your attention!
+\vskip30pt
+\begin{Verbatim}[commandchars=\\\{\}]
+
+
+RCPT TO:<john.ogness@linutronix.de>
+\end{Verbatim}
+\end{frame}
+
+\end{document}