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Théophile Bastian 2018-09-03 18:01:37 +02:00
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@ -8,6 +8,8 @@
\usepackage{amsmath} \usepackage{amsmath}
\usepackage{amsfonts} \usepackage{amsfonts}
\usepackage{amssymb} \usepackage{amssymb}
\usepackage{booktabs}
\usepackage{makecell}
\usepackage{../shared/my_listings} \usepackage{../shared/my_listings}
%\usepackage{../shared/my_hyperref} %\usepackage{../shared/my_hyperref}
@ -15,6 +17,9 @@
\usepackage{../shared/common} \usepackage{../shared/common}
\usepackage{../shared/todo} \usepackage{../shared/todo}
\renewcommand\theadalign{c}
\renewcommand\theadfont{\scriptsize\bfseries}
\setbeamertemplate{navigation symbols}{} \setbeamertemplate{navigation symbols}{}
\newcommand{\thenalert}[1]{\only<1>{#1}\only<2>{\alert{#1}}} \newcommand{\thenalert}[1]{\only<1>{#1}\only<2>{\alert{#1}}}
@ -242,6 +247,50 @@ unwind_context_t _eh_elf(
\end{itemize} \end{itemize}
\end{frame} \end{frame}
\begin{frame}{Compilation choices}
\textbf{In order to keep the compiler \alert{simple} and \alert{easily
testable}, the whole DWARF5 instruction set is not supported.}
\begin{itemize}
\item Tailored for \alert{x86\_64} (while DWARF is
architecture-agnostic)
\item Only supports \alert{unwinding registers}: \reg{rip}, \reg{rsp},
\reg{rbp}, \reg{rbx}
\begin{itemize}
\item[$\leadsto$] suitable for perf, not for gdb
\end{itemize}
\item Supports the \alert{wide majority} ($> 99.9\%$) of instructions
used (see later)
\begin{itemize}
\item Only supports few common expressions: already $~ 90\,\%$
of expressions used
\end{itemize}
\end{itemize}
\end{frame}
\begin{frame}[fragile]{A word on memory maps}
\textbf{Various functions come from various ELFs}\\
\pause{}
\hfill{}\textbf{\ldots{}and thus various \ehelfs{}}
\begin{lstlisting}[language=, numbers=none]
55c81b11e000-55c81b126000 000k /usr/bin/cat
55c81b325000-55c81b326000 007k /usr/bin/cat
55c81b326000-55c81b327000 008k /usr/bin/cat
55c81bcf3000-55c81bd14000 000k [heap]
7f8a5b4ed000-7f8a5b50f000 000k /usr/lib/libc-2.28.so
7f8a5b50f000-7f8a5b65a000 022k /usr/lib/libc-2.28.so
7f8a5b65a000-7f8a5b6a6000 16dk /usr/lib/libc-2.28.so
7f8a5b6ec000-7f8a5b6ee000 000k /usr/lib/ld-2.28.so
7f8a5b6ee000-7f8a5b70d000 002k /usr/lib/ld-2.28.so
7f8a5b70d000-7f8a5b715000 021k /usr/lib/ld-2.28.so
7ffc8a66b000-7ffc8a68c000 000k [stack]
7ffc8a74a000-7ffc8a74d000 000k [vvar]
7ffc8a74d000-7ffc8a74f000 000k [vdso]
\end{lstlisting}
\end{frame}
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\subsection{Outlining} \subsection{Outlining}
@ -338,7 +387,183 @@ unwind_context_t _eh_elf(
\end{itemize} \end{itemize}
\end{frame} \end{frame}
\begin{frame}{libunwind implementation}
\begin{itemize}
\item \alert{libunwind}: \textit{de facto} standard library for
unwinding
\item Uses DWARF in background
\item \alert{Used by perf} as a backend for unwinding
\pause{}\vspace{1em} \item{} Easiest way to use \ehelfs{} in perf:
\alert{implement an alternative libunwind}
\item{} Result: \alert{alternative implementation} of libunwind, nearly
plug-and-play!
\end{itemize}
\end{frame}
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\section{Results}
\begin{frame}{Time performance}
\small
\centering
\begin{tabular}{l r r r r r}
\toprule
\thead{Unwinding method} & \thead{Frames \\ unwound}
& \thead{Tot.\ time \\ ($\mu s$)}
& \thead{Avg. \\ time / frame \\ ($ns$)}
& \thead{Time \\ ratio} \\
\midrule
\alert{\ehelfs{}}
& 23506 % Frames unwound
& 14837 % Total time
& 631 % Avg time
& 1
\\
\prog{libunwind}, \alert{cached}
& 27058 % Frames unwound
& 441601 % Total time
& 16320 % Avg time
& \alert{25.9}
\\
\prog{libunwind}, \alert{uncached}
& 27058 % Frames unwound
& 671292 % Total time
& 24809 % Avg time
& \alert{39.3}
\\
\bottomrule
\end{tabular}
\end{frame}
\begin{frame}{Space performance}
\begin{center}
\begin{tabular}{r r r r r r}
\toprule
\thead{Object}
& \thead{Original \\ program size \\ (KiB)}
& \thead{Original \\ \lstc{.eh\_frame} \\ (KiB)}
& \thead{Generated \\ \ehelf{} \\ (KiB)}
& \thead{\% \\ original \\ size}
& \thead{Growth \\ factor} \\
\midrule
libc
& 1\,434 & 130.1 & 313.2 & 21.88 & 2.41 \\
libpthread
& 58.1 & 11.6 & 25.4 & 43.71 & 2.19 \\
ld
& 129.6 & 9.6 & 28.6 & 22.09 & 2.97 \\
hackbench
& 2.9 & 0.555 & 2.8 & 93.87 & 4.99 \\
Total
& 1\,638 & 151.8 & 370.0 & 22.81 & \alert{2.44} \\
\bottomrule
\end{tabular}
\end{center}
\end{frame}
\newcommand{\ofsupp}[1]{$\left[\text{#1}\right]$}
\begin{frame}{Instructions coverage}
\scriptsize\centering
\begin{tabular}{r r r r r r}
\toprule
\thead{}
& \thead{Undef}
& \thead{Same \\ value}
& \thead{Offset}
& \thead{Val \\ offset}
& \thead{Reg}
\\
\midrule
\makecell{Only supp. \\ columns} \vspace{.4em}
& 1698 (0.006\,\%)
& 0
& 30\,M (99.9\,\%)
& 0
& 14 (0\,\%)
\\
All columns
& 1698 (0.003\,\%)
& 0
& 55\,M (99.9\,\%)
& 0
& 22 (0\,\%)
\\
\bottomrule
\toprule
\thead{}
& \thead{Expr \\ \ofsupp{supported}}
& \thead{Val \\ expr}
& \thead{Archi.}
& & \thead{Total}
\\
\midrule
\makecell{Only supp. \\ columns} \vspace{.4em}
& \makecell{4475 (0.015\,\%) \\ \ofsupp{81.4\,\%}}
& 0
& 0
& & 30044442
\\
All columns
& \makecell{12367 (0.02\,\%) \\ \ofsupp{91.7\,\%}}
& 0
& 0
& & 54680492
\\
\bottomrule
\end{tabular}
\vspace{2em}\pause{}
\textbf{Among \alert{4000} randomly sampled filed, only \alert{24}
containing unsupported instructions}
\end{frame}
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\section{A glance at future work} \section{A glance at future work}
\begin{frame}{What next?}
\begin{itemize}
\item \alert{Outlining} was super efficient for
compactness\ldots{} Worth trying on standard DWARF\@?
\item Implement a release-ready, packageable, easy to use version of
perf with \ehelfs{} and submit it for inclusion
\item{} Measure \alert{C++ exceptions overhead} precisely in common
software
\item{} Implement \alert{\ehelfs{}} support for \alert{C++ runtime}
exception handling
\item{} \ldots{}and many more possibilities to explore!
\end{itemize}
\end{frame}
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\section*{}
\begin{frame}
\begin{columns}[c]
\begin{column}{0.35\textwidth}
\includegraphics[width=\linewidth]{img/keep_breathing}
\end{column}
\begin{column}{0.65\textwidth}
\begin{center}
\huge
And remember\ldots{}
\smallskip
DWARF is slow!
\end{center}
\end{column}
\end{columns}
\begin{center}
\Huge\bfseries
Thank you!
\end{center}
\end{frame}
\end{document} \end{document}