Skip to content

Commit

Permalink
Boot time slides: updates from previous session notes
Browse files Browse the repository at this point in the history 
Signed-off-by: Michael Opdenacker <michael.opdenacker@bootlin.com>
  • Loading branch information
@michaelopdenacker
michaelopdenacker committed Jun 20, 2021
1 parent 8da72aa commit 8fd69c1
Show file tree
Hide file tree
Showing 6 changed files with 106 additions and 53 deletions.
3 changes: 1 addition & 2 deletions common/boneblack-sdcard-preparation.tex
View file
Expand Up @@ -8,8 +8,7 @@ \section{Prepare the SD card}
the requirements of the AM335x SoC so that it can find the bootloader in
this partition. It should be a FAT32 partition. We will store the
bootloader (\code{MLO} and \code{u-boot.img}), the kernel image
(\code{zImage}), the Device Tree (\code{am335x-boneblack.dtb}) and a
special U-Boot script for the boot.
(\code{zImage})and the Device Tree (\code{am335x-boneblack.dtb}).

\item A second partition for the root filesystem. It can use
whichever filesystem type you want, but for our system, we'll use
Expand Down
21 changes: 9 additions & 12 deletions slides/boot-time-bootloader/boot-time-bootloader.tex
View file
@@ -1,5 +1,7 @@
\section{Bootloader optimizations}

\subsection{Generic bootloader optimizations}

\begin{frame}
\frametitle{Bootloader}
\begin{itemize}
Expand Down Expand Up @@ -32,11 +34,6 @@ \section{Bootloader optimizations}
\item Remove the boot delay:\\
\code{setenv bootdelay 0}
\item This usually saves several seconds!
\item Before you do that, recompile U-Boot with
\kconfig{CONFIG_ZERO_BOOTDELAY_CHECK}, documented in
\code{doc/README.autoboot}. It allows to stop the autoboot
process by hitting a key even if the boot delay is set to
\code{0}.
\end{itemize}
\end{frame}

Expand Down Expand Up @@ -66,13 +63,13 @@ \section{Bootloader optimizations}
\begin{frame}
\frametitle{Bootloader: copy the exact kernel size}
\begin{itemize}
\item When copying the kernel from flash to RAM, we still see
\item When copying the kernel from {\bf raw} flash to RAM, we still see
many systems that copy too many bytes, not taking the
exact kernel size into account.
\item In U-Boot, use the \code{nboot} command:\\
\code{nboot ramaddr 0 nandoffset}
\item U-Boot using the kernel size information stored in the
\code{uImage} header to know how many bytes to copy.
\item A solution is to store the exact size of the kernel in an environment
variable, and use it a kernel loading time.
\item Of course, that's not needed when the kernel is loaded from a
filesystem, which knows how big the file is.
\end{itemize}
\end{frame}

Expand Down Expand Up @@ -151,9 +148,9 @@ \section{Bootloader optimizations}
\frametitle{Further U-Boot optimizations}
\begin{itemize}
\item Silence U-Boot console output. You will need to compile
U-Boot with \kconfig{CONFIG_SILENT_CONSOLE} and
U-Boot with \projconfig{u-boot}{CONFIG_SILENT_CONSOLE} and
\code{setenv silent yes}.\\
See \code{doc/README.silent} for details.
See \projfile{u-boot}{doc/README.silent} for details.
\end{itemize}
\end{frame}

Expand Down
8 changes: 5 additions & 3 deletions slides/boot-time-filesystems/boot-time-filesystems.tex
View file
Expand Up @@ -77,6 +77,8 @@ \section{Filesystem optimizations}
from 16 s to 0.8 s for a 128 MB partition.
\item Rather poor read and write performance,\\
compared to YAFFS2 and UBIFS.
\item JFFS2 only makes sense on small storage space,
where UBI would have too much overhead.
\end{itemize}
\end{frame}

Expand All @@ -92,18 +94,18 @@ \section{Filesystem optimizations}

\begin{frame}
\frametitle{UBIFS}
For raw flash storage
For raw flash storage, on top of the UBI layer
\begin{itemize}
\item Advantages:
\begin{itemize}
\item Good read and write performance (similar to YAFFS2)
\item Other advantages: better for wear leveling (can operate on the
whole UBI space, not only within a single partition).
whole UBI space, not only within a single partition).
\end{itemize}
\item Drawbacks:
\begin{itemize}
\item Not appropriate for small partitions (too much metadata
overhead). Use JFFS2 or JAFFS2 instead.
overhead). Use JFFS2 or JAFFS2 instead.
\item Not so good mount time, because of the time needed
to initialize UBI ({\em UBI Attach}: at boot time or running
\code{ubi_attach} in user space).
Expand Down
38 changes: 15 additions & 23 deletions slides/boot-time-measuring/boot-time-measuring.tex
View file
Expand Up @@ -55,6 +55,7 @@ \section{Measuring}
\frametitle{Time measurement equipment: serial port}
\begin{columns}
\column{0.75\textwidth}
\small
\begin{itemize}
\item Useful when you don't have monitoring hardware, or don't want to make
take any risk connecting wires to the hardware.
Expand All @@ -63,40 +64,28 @@ \section{Measuring}
runs on a PC connected to the serial port.
\item On the board, requires a real serial port (directly connected to the CPU),
immediately usable from the earliest parts of the boot process.
Attaching a USB-to-serial dongle to a USB {\bf host} port on
the device won't do: USB is available much later and messages
go through more complex software stacks (loss of time accuracy).
\item Limitation: won't be able to time the "Power on" event in
an accurate way. But acceptable as you can assume that
the time to run the first stage bootloader is constant.
\end{itemize}
\column{0.25\textwidth}
% From https://openclipart.org/detail/173570/serial-db9-female-by-deusinvictus-173570
\includegraphics[width=\textwidth]{slides/boot-time-measuring/serial_db9_female.pdf}
\end{columns}
\end{frame}

\begin{frame}
\frametitle{Time measurement equipment: USB to serial}
\begin{columns}
\column{0.65\textwidth}
\begin{itemize}
\item Serial ports over USB {\bf device} are fine if there's an on-board
serial-to-USB chip directly connected to the CPU serial port (very frequent).
\item Attaching a USB-to-serial dongle to a USB {\bf host} port on
the device won't do: USB is available much later and messages
go through more complex software stacks (loss of time accuracy).
\item All development boards have a standard or USB serial port.
\end{itemize}
\column{0.35\textwidth}
% From https://openclipart.org/detail/135721/usb-cable-by-gsagri04
\includegraphics[width=\textwidth]{slides/boot-time-measuring/GS_USB_Cable.pdf}
\includegraphics[width=\textwidth]{slides/boot-time-measuring/serial_db9_female.pdf}\\
\vspace{1cm}
% From https://openclipart.org/detail/135721/usb-cable-by-gsagri04
\includegraphics[width=\textwidth]{slides/boot-time-measuring/GS_USB_Cable.pdf}
\end{columns}
\end{frame}

\begin{frame}
\frametitle{grabserial}
\url{https://elinux.org/Grabserial} (by Tim Bird)
\begin{itemize}
\item A Python script to add timestamps to messages coming from a
serial console.
\item A Python script to add timestamps to messages received on a
serial console.
\item Key advantage: starts counting very early (bootstrap and bootloader)
\item Another advantage: no overhead on the target, because run on the host machine.
\item Drawbacks: may not be precise enough. Can't measure power up time.
Expand All @@ -121,7 +110,8 @@ \section{Measuring}
\begin{itemize}
\item You can interrupt \code{grabserial} manually (with
\code{[Ctrl][c]}) when you have gone far enough.
\item The \code{-m} and \code{-q} options actually expect a regular expression.
\item The \code{-m} ({\bf m}atch start pattern) and \code{-q} ({\bf
q}uit pattern) options actually expect a regular expression.
A normal string may not match in the middle of a line.
\item Example: you may have to replace \code{-m "Starting kernel"} by
\code{-m ".*Starting Kernel.*"}.
Expand All @@ -134,7 +124,9 @@ \section{Measuring}
\begin{itemize}
\item \code{time} for measuring application time
\item \code{strace} for application tracing
\item \code{bootchartd} for tracing the execution of system services
\item \code{bootchartd} for tracing the execution of system services.
\item More specifically, \code{systemd-analyze} if your system
is started with {\em Systemd}.
\item \kconfig{CONFIG_PRINTK_TIME} and \code{initcall_debug} for
tracing kernel code and functions.
\end{itemize}
Expand Down
69 changes: 67 additions & 2 deletions slides/boot-time-measuring/using-grabserial.dia
View file
Expand Up @@ -227,12 +227,12 @@
<dia:point val="10.1,5.975"/>
</dia:attribute>
<dia:attribute name="obj_bb">
<dia:rectangle val="10.1,5.23644;31.0975,15.7728"/>
<dia:rectangle val="10.1,5.21303;31.1209,15.8196"/>
</dia:attribute>
<dia:attribute name="text">
<dia:composite type="text">
<dia:attribute name="string">
<dia:string>#$ ~/bin/grabserial -d /dev/ttyACM0 -m RomBOOT -t -e 30
<dia:string>#$ ~/bin/grabserial -d /dev/ttyACM0 -m RomBOOT -t -e 30 -o boot.log
[0.000002 0.000002] RomBOOT
[0.054440 0.054440]
[0.054594 0.000154]
Expand Down Expand Up @@ -662,5 +662,70 @@ the previous time stamp#</dia:string>
<dia:enum val="3"/>
</dia:attribute>
</dia:object>
<dia:object type="Standard - ZigZagLine" version="1" id="O18">
<dia:attribute name="obj_pos">
<dia:point val="26.95,6.2"/>
</dia:attribute>
<dia:attribute name="obj_bb">
<dia:rectangle val="26.5882,6.15;39.5,8.75"/>
</dia:attribute>
<dia:attribute name="orth_points">
<dia:point val="26.95,6.2"/>
<dia:point val="26.95,7.35"/>
<dia:point val="39.45,7.35"/>
<dia:point val="39.45,8.7"/>
</dia:attribute>
<dia:attribute name="orth_orient">
<dia:enum val="1"/>
<dia:enum val="0"/>
<dia:enum val="1"/>
</dia:attribute>
<dia:attribute name="autorouting">
<dia:boolean val="false"/>
</dia:attribute>
<dia:attribute name="start_arrow">
<dia:enum val="22"/>
</dia:attribute>
<dia:attribute name="start_arrow_length">
<dia:real val="0.5"/>
</dia:attribute>
<dia:attribute name="start_arrow_width">
<dia:real val="0.5"/>
</dia:attribute>
</dia:object>
<dia:object type="Standard - Text" version="1" id="O19">
<dia:attribute name="obj_pos">
<dia:point val="38.025,9.49856"/>
</dia:attribute>
<dia:attribute name="obj_bb">
<dia:rectangle val="38.025,8.76;42.4025,10.4963"/>
</dia:attribute>
<dia:attribute name="text">
<dia:composite type="text">
<dia:attribute name="string">
<dia:string>#Copy the output
to a file too#</dia:string>
</dia:attribute>
<dia:attribute name="font">
<dia:font family="Latin Modern Sans" style="0" name="Courier"/>
</dia:attribute>
<dia:attribute name="height">
<dia:real val="0.80000000000000004"/>
</dia:attribute>
<dia:attribute name="pos">
<dia:point val="38.025,9.49856"/>
</dia:attribute>
<dia:attribute name="color">
<dia:color val="#0000ffff"/>
</dia:attribute>
<dia:attribute name="alignment">
<dia:enum val="0"/>
</dia:attribute>
</dia:composite>
</dia:attribute>
<dia:attribute name="valign">
<dia:enum val="3"/>
</dia:attribute>
</dia:object>
</dia:layer>
</dia:diagram>
20 changes: 9 additions & 11 deletions slides/boot-time-principles/boot-time-principles.tex
View file
Expand Up @@ -77,17 +77,15 @@ \section{Principles}
\begin{frame}
\frametitle{Build automation}
\begin{itemize}
\item Very important to automate the way the root filesystem is built,
if not done yet. That's always the first thing we do in boot time
reduction projects, and it's worth investing 1 or 2 days doing
this.
\item Otherwise, you may lose existing optimizations or introduce new bugs
when making further optimizations. Without a build system,
you will waste a lot of time too.
\item Can be done through build systems such as Buildroot or Yocto,
or using the original build automation of the project.
\item Can also be done for kernel and bootloader optimizations, though
the need is less critical.
\item Build automation is a very important part of a successful project.
\item So, through the build system, you should automate any remaining
manual step and all the new optimizations that you will implement
to reduce boot time. Without such automation, you may forget some
optimizations, or introduce new bugs when making further optimizations.
\item Boot time optimization projects required countless rebuilds too,
automating image generation will save a lot of time too.
\item Kernel and bootloader compiling and optimizations can also be
taken care of by the build system, though the need is less critical.
\end{itemize}
\end{frame}

Expand Down

0 comments on commit 8fd69c1

Please sign in to comment.