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Doc: More troubleshooting hints for perf profiler

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Apparently the chosen event type influences the stability of the
recording process and you can change the event type using the
additional arguments.

Change-Id: I0e1982d4d469e1e4d17e2aa01d3c5166ce8817a3
Reviewed-by: Venugopal Shivashankar <venugopal.shivashankar@digia.com>
This commit is contained in:
Ulf Hermann
2015-05-15 15:36:19 +02:00
parent 69d5fc1257
commit f335088ce1
1 changed files with 13 additions and 3 deletions
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16
doc/src/analyze/cpu-usage-analyzer.qdoc
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@@ -271,9 +271,19 @@
\li Some versions of Perf will not start recording unless given a
certain minimum sampling frequency. Try with a
\uicontrol {Sampling Frequency} of 1000.
\li On some devices, Perf support is not very stable and the Linux
kernel may randomly fail to record data after some time. Reboot the
device and try again.
\li On some devices, for example Boundary Devices i.MX6 Boards, the
Perf support is not very stable and the Linux kernel may randomly
fail to record data after some time. Perf can use different types
of events to trigger samples. You can get a list of available event
types by running \c {perf list} on the device and add
\c {-e <event type>} to the \uicontrol {Additional arguments} field
to change the event type to be used. The choice of event type
affects the performance and stability of the sampling.
\c {-e cpu-clock} is a safe but relatively slow option as it
does not use the hardware performance counters, but drives the
sampling from software. After the sampling has failed, reboot the
device. The kernel may have disabled important parts of the
performance counters system.
\endlist
Output from the helper program that processes the data is displayed in the