[bootlin/training-materials updates] master: Toolchain optimization updates (4e91d045)

[Michael Opdenacker]

Repository : https://github.com/bootlin/training-materials
On branch  : master
Link       : https://github.com/bootlin/training-materials/commit/4e91d0454cad88d1f08a4605dbd775013e21729d

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commit 4e91d0454cad88d1f08a4605dbd775013e21729d
Author: Michael Opdenacker <michael.opdenacker at bootlin.com>
Date:   Wed Apr 7 11:51:32 2021 +0200

    Toolchain optimization updates
    
    Signed-off-by: Michael Opdenacker <michael.opdenacker at bootlin.com>


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4e91d0454cad88d1f08a4605dbd775013e21729d
 .../boot-time-toolchain2/boot-time-toolchain2.tex  | 32 ++++++++++++----------
 1 file changed, 17 insertions(+), 15 deletions(-)

diff --git a/slides/boot-time-toolchain2/boot-time-toolchain2.tex b/slides/boot-time-toolchain2/boot-time-toolchain2.tex
index 4e94ec4a..b467811e 100644
--- a/slides/boot-time-toolchain2/boot-time-toolchain2.tex
+++ b/slides/boot-time-toolchain2/boot-time-toolchain2.tex
@@ -6,13 +6,16 @@
 This gives you the best time that can possibly be achieved (with the fastest storage).
 \end{frame}
 
-\setuplabframe {Trying a Thumb2 toolchain}
+\setuplabframe {Toolchain optimizations}
 {
 \begin{itemize}
 \item Measure filesystem and \code{ffmpeg} binary size. Time
       the execution of the application.
 \item Re-compile the root filesystem using a Thumb2 toolchain
-\item Measure size and time again.
+\item Re-compile the root filesystem with the {\em Musl}
+      C library instead of {\em uClibc}
+\item Find the best toolchain in terms of size and execution time.
+\item Have Buildroot generate an external toolchain ({\em SDK})
 \end{itemize}
 }
 
@@ -22,30 +25,29 @@ This gives you the best time that can possibly be achieved (with the fastest sto
 \begin{itemize}
 \item Testcase: root filesystem with \code{ffmpeg} and associated
       libraries (from our training labs)
-\item Compiled with gcc 7.4, generating {\em ARM} code:\\
-      Total filesystem size: 3.79 MB\\
+\item Compiled with gcc 9.3, generating {\em ARM} code:\\
+      Total filesystem size: 17.6 MB\\
       \code{ffmpeg} size: 227 KB
-\item Compiled with gcc 7.4, generating {\em Thumb2} code:\\
-      Total filesystem size: 3.10 MB (-18 \%)\\
+\item Compiled with gcc 9.3, generating {\em Thumb2} code:\\
+      Total filesystem size: 14.3 MB (-18 \%)\\
       \code{ffmpeg} size: 183 KB (-19 \%)
 \item Performance aspect: performance apparently slightly improved with Thumb2
-      (approximately less than 5 \%, but there are slight variations in measured
+      (about 2 \%, but there are slight variations in measured
       execution time, for one run to another).
 \end{itemize}
 \end{frame}
 
 \begin{frame}
 \frametitle{Lessons from labs: musl vs uClibc}
-{\em Tested while preparing the labs (too long to do this during the
-class)}\\
-
-Tried to replace {\em uClibc} by {\em musl} in our video player lab:
+Replacing {\em uClibc} by {\em musl} in our video player lab, keeping
+{\em Thumb2}:
 \begin{itemize}
-   \item musl library size: 680 KB (size of the \code{tar} archive for \code{lib/})
-   \item uClibc library size: 570 KB
-   \item uClibc saves 110 KB (useful), but otherwise no other significant change
+   \item Total system size with {\em uClibc}: 17.3 MB
+   \item Total system size with {\em Musl}: 14.4 MB
+   \item uClibc saves 80 KB (useful), but otherwise no other significant change
     in filesystem and code size. Not a surprise when the system is mostly filled
     with binaries relying on shared libraries.
 \end{itemize}
-We stuck to {\em uClibc}!
+Switching to {\em Musl} as it is supposed to allow for smaller static
+binariess, which will be useful in later labs.
 \end{frame}