[bootlin/training-materials updates] master: Real-time lab: use chrt before adding load (ab0448b6)

[Michael Opdenacker]

Repository : https://github.com/bootlin/training-materials
On branch  : master
Link       : https://github.com/bootlin/training-materials/commit/ab0448b6cf93b3ac99288277f6577247233ca329

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commit ab0448b6cf93b3ac99288277f6577247233ca329
Author: Michael Opdenacker <michael.opdenacker at bootlin.com>
Date:   Thu May 20 18:32:11 2021 +0200

    Real-time lab: use chrt before adding load
    
    - Making more sense in my opinion, running the test
      program without chrt just gives meaningless results.
    
    Signed-off-by: Michael Opdenacker <michael.opdenacker at bootlin.com>


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ab0448b6cf93b3ac99288277f6577247233ca329
 labs/sysdev-real-time/sysdev-real-time.tex | 12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

diff --git a/labs/sysdev-real-time/sysdev-real-time.tex b/labs/sysdev-real-time/sysdev-real-time.tex
index d0f4ed1d..2ece8cc3 100644
--- a/labs/sysdev-real-time/sysdev-real-time.tex
+++ b/labs/sysdev-real-time/sysdev-real-time.tex
@@ -159,15 +159,17 @@ Now, do the following tests:
 \begin{itemize}
 \item Run the \code{rttest} program with nothing special and write
   down the results.
-\item Run \code{rttest} again and at the same time, add some workload
-  to the board, by running \code{/root/doload 300 > /dev/null 2>&1 &}
+\item Run \code{rttest} once again, but this time
+  using the \code{SCHED_FIFO} scheduling class at priority
+  \code{99}, using the \code{chrt} command. Without this, the kernel
+  doesn't know that your program should be given absolute priority
+  over other processes.
+\item Run \code{rttest} again through \code{chrt}, but right before,
+  add some extra load, by running \code{/root/doload 300 > /dev/null 2>&1 &}
   on the board, and using \code{netcat 192.168.0.100 5566} on your
   workstation in order to flood the network interface of the Xplained
   board (where \code{192.168.0.100} is the IP address of the Xplained
   board).
-\item Run \code{rttest} once again with the workload, but by running
-  the program in the \code{SCHED_FIFO} scheduling class at priority
-  \code{99}, using the \code{chrt} command.
 \end{itemize}
 
 \subsection{Testing the preemptible kernel}