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Document perf kernel parameters.

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Bartosz Taudul 2021-05-20 02:00:49 +02:00
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manual/tracy.tex
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@ -1843,6 +1843,20 @@ By default sampling is performed at 8 kHz frequency on Windows (which is the max
Call stack sampling may be disabled by using the \texttt{TRACY\_NO\_SAMPLING} define.
\begin{bclogo}[
noborder=true,
couleur=black!5,
logo=\bcbombe
]{Linux sampling rate limits}
The operating system may decide that sampling is taking too much CPU time and reduce the allowed sampling rate. This can be seen in \texttt{dmesg} output as:
\texttt{perf: interrupt took too long, lowering kernel.perf\_event\_max\_sample\_rate to \emph{value}}.
If the \emph{value} goes below the sample rate Tracy wants to use, sampling will be silently disabled. To make it work again, you can set an appropriate value in the \texttt{kernel.perf\_event\_max\_sample\_rate} kernel parameter, using the \texttt{sysctl} utility.
Should you want to disable this mechanism, you can set the \texttt{kernel.perf\_cpu\_time\_max\_percent} parameter to zero. Be sure to read what this would do, as it may have serious consequences that you should be aware of.
\end{bclogo}
\subsubsection{Executable code retrieval}
\label{executableretrieval}