The Sampling Enabling Product (SEP) is a powerful tool for collecting event based profiling data on a system. SEP uses a hardware based, low-overhead and system-wide collector that helps identify the modules and functions that are consuming the most time. This article discusses several techniques that we have found useful when troubleshooting issues with SEP.
In troubleshooting SEP issues on embedded Linux* systems, there are several steps you should take:
Loading the sep driver
Run the command: “./insmod-sep3” .
Increasing the size of the /tmp partition
Configuring stack size
Disable nmi watchdog timer
The NMI Watchdog can be used in the Linux* kernel to periodically detect if the CPU is locked. When CPU-locking occurs, the NMI Watchdog service does the following:
However NMI Watchdog needs to use a PMU counter, so other performance tools including SEP can’t use PMU event-based sampling data collections.
To disable the nmi watchdog timer use the following command:
echo 0 > /proc/sys/kernel/nmi_watchdog
Allow kernel symbols to be visible to data collector
if “cat /proc/sys/kernel/kptr_restrict” is anything but 0, then
echo 0 > /proc/sys/kernel/kptr_restrict
This allows the kernel symbols to be visible to the data collector. If not set, you will see all the kernel samples attributed to “Unknown module” or “Other64” or “Other32”.
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Notice revision #20110804