[bootlin/training-materials updates] master: preempt-rt : Refactor hwlatdetect, NMI, and introduce rtla (368a40e8)

[Maxime Chevallier]

Repository : https://github.com/bootlin/training-materials
On branch  : master
Link       : https://github.com/bootlin/training-materials/commit/368a40e853a3a45f0a68960a43173d419f1c20f6

>---------------------------------------------------------------

commit 368a40e853a3a45f0a68960a43173d419f1c20f6
Author: Maxime Chevallier <maxime.chevallier at bootlin.com>
Date:   Mon Jan 9 22:33:20 2023 +0100

    preempt-rt : Refactor hwlatdetect, NMI, and introduce rtla
    
    Signed-off-by: Maxime Chevallier <maxime.chevallier at bootlin.com>


>---------------------------------------------------------------

368a40e853a3a45f0a68960a43173d419f1c20f6
 .../realtime-linux-benchmarking.tex                | 49 ++++++++++++++++++----
 .../realtime-linux-hardware.tex                    |  3 +-
 2 files changed, 43 insertions(+), 9 deletions(-)

diff --git a/slides/realtime-linux-benchmarking/realtime-linux-benchmarking.tex b/slides/realtime-linux-benchmarking/realtime-linux-benchmarking.tex
index edb2d02a..2df43f88 100644
--- a/slides/realtime-linux-benchmarking/realtime-linux-benchmarking.tex
+++ b/slides/realtime-linux-benchmarking/realtime-linux-benchmarking.tex
@@ -73,6 +73,41 @@ cat /sys/kernel/tracing/tracing_max_latency
   \end{itemize}
 \end{frame}
 
+\begin{frame}
+	\frametitle{hwlatdetect}
+	Tool provided by \code{rt-tests}, relying on a dedicated kernel feature
+	\begin{itemize}
+		\item Allows detecting NMIs and Hardware latencies the kernel is normally unaware of
+		\item Runs a loop on all CPU cores with local interrupts disabled
+		\item Only NMIs and Hardware Latencies can interrupt the loop
+		\item Samples a high precision timer and looks for large gaps between samples
+		\item Useful to benchmark and validate a hardware platform
+		\item Must \textbf{not} be used in production environment, introduces huge latencies
+	\end{itemize}
+\end{frame}
+
+\begin{frame}
+	\frametitle{osnoise}
+	\begin{itemize}
+		\item Gives an overview of "noise" sources from the Kernel and the Hardware
+		\item Uses a similar measurement loop as \code{hwlatdetect}
+		\item Uses \code{tracepoints} to detect the source of noise :
+			\begin{itemize}
+				\item Thread Latency : Latencies due to the measuring thread being preempted
+				\item SoftIRQ Latency : Latencies due to softIRQ processing
+				\item IRQ Latency : Latencies introduced by IRQs
+				\item NMI Latency : Latencies introduced by NMIs
+				\item Hardware Latency : Latencies that aren't explained by any of the above
+			\end{itemize}
+		\item \code{trace-cmd start -p osnoise} : Start recording os noise events
+		\item \code{trace-cmd start -p osnoise -e osnoise} : Start recording noise events and trace their cause
+	\end{itemize}
+\end{frame}
+
+\begin{frame}
+	\frametitle{timerlat}
+\end{frame}
+
 \begin{frame}
 	\frametitle{kernelshark}
 	\begin{itemize}
@@ -86,16 +121,14 @@ cat /sys/kernel/tracing/tracing_max_latency
 \end{frame}
 
 \begin{frame}
-	\frametitle{hwlatdetect}
-	Tool provided by \code{rt-tests}, relying on a dedicated kernel feature
+	\frametitle{rtla}
+	\textbf{R}eal\textbf{T}ime \textbf{L}inux \textbf{A}nalysis tool
 	\begin{itemize}
-		\item Allows detecting NMIs, that the kernel is normally unaware of
-		\item Runs a loop on all CPU cores with local interrupts disabled
-		\item Only NMIs can interrupt the loop
-		\item Samples a high precision timer and looks for large latencies
-		\item Useful to benchmark and validate a hardware platform
-		\item Must \textbf{not} be used in production environment, introduces huge latencies
+		\item Developped by Daniel Bristot de Oliveira
+		\item High-level interface to the \code{timerlat} and \code{osnoise} tracers
+		\item \code{rtla osnoise|timerlat top|hist} gives high-level view of noise and latencies
 	\end{itemize}
+
 \end{frame}
 
 \begin{frame}
diff --git a/slides/realtime-linux-hardware/realtime-linux-hardware.tex b/slides/realtime-linux-hardware/realtime-linux-hardware.tex
index d47cd931..3e0e22a7 100644
--- a/slides/realtime-linux-hardware/realtime-linux-hardware.tex
+++ b/slides/realtime-linux-hardware/realtime-linux-hardware.tex
@@ -14,7 +14,7 @@
 
 \begin{frame}
 	\frametitle{Non-Maskable Interrupts}
-	Non-Maskable Interrupts can't be disabled, and are often transparent to the OS
+	Non-Maskable Interrupts can't be disabled, and can be transparent to the OS
 	\begin{itemize}
 		\item Common NMIs are System Management Interrupts (SMIs)
 		\item SMIs run in a dedicated context, the System Management Mode
@@ -22,6 +22,7 @@
 		\item Used for thermal management, remote configuration, and are very opaque
 		\item Can't be prevented, predicted, monitored or controlled
 		\item Modern CPUs can expose a NMI counter
+		\item Kernel-processed NMIs can be instrumented with \code{ftrace}
 		\item \code{hwlatdetect} can help measure the NMIs on a given system
 	\end{itemize}
 	% SMM, SMI