labs/sysdev-application-development-and-debugging: add details about …

…perf

Signed-off-by: Thomas Petazzoni <[email protected]>

labs/sysdev-application-development-and-debugging/sysdev-application-development-and-debugging.tex

@@ -455,7 +455,9 @@ \section{Profiling the application with perf}
 \end{bashinput}
 
 See the time spent in various kernel (\code{[k]}) and userspace
-(\code{[.]}) functions.
+(\code{[.]}) functions. The details of the kernel functions is not
+visible, but additional symbol information can be added by building
+the kernel with the \code{CONFIG_KALLSYMS_ALL} option enabled.
 
 Now, let's profile the whole system. First, make sure that the system is
 currently playing audio. Then SSH to your board and run \code{perf top}