[LITMUS^RT] /st_trace can not find sched_trace 0-7

[Glenn Elliott]

On Dec 15, 2013, at 9:13 AM, Luo, Zheng <luozheng at wustl.edu> wrote:

> Hi every,
> 
> I try to use the st_trace, however the program can not start correctly. I think when I compile the kernel, I already enable the trace flag (I attached the image). However it still can not find the sched_trace 0-7.
> 
> I send the screen shots and the .config too. Can anyone tell me that where I did wrong?
> 
> 
> <Screenshot 2013-12-15 08:04:15.png>
> 
> <Screenshot 2013-12-15 08:03:17.png>
> 
> 
> 
> Zheng Luo
> <config>_______________________________________________
> litmus-dev mailing list
> litmus-dev at lists.litmus-rt.org
> https://lists.litmus-rt.org/listinfo/litmus-dev



Hi Zheng,

Take a look at litmus-rt/litmus/Kconfig.  In the file you can see the configurable compile-time options in Litmus and their dependencies.  You need to select CONFIG_SCHED_TASK_TRACE to enable the tracing features you want.  As you can see in the Kconfig, CONFIG_SCHED_TASK_TRACE depends upon CONFIG_FEATHER_TRACE.  Looking at your screenshot, I see that (1) CONFIG_FEATHER_TRACE is not set and (2) you don’t even have the option to select CONFIG_FEATHER_TRACE.  This is because CONFIG_FEATHER_TRACE has the dependency “!CONFIG_RELOCATABLE”  (again, look at the FEATHER_TRACE entry in the Kconfig).  So:

1) Disable a relocatable kernel.  I can’t recall where it is exactly, but it is probably somewhere in the general settings.  In the menuconfig, you can hit “/“ and search (just like how search works in vim) for the string RELOCATABLE.
2) Enable feather trace.
3) Enable sched task trace

Note that “TRACE() debugging” generates text-based logs that can be read from /dev/litmus/log.  It is purely for debugging.  If you need to take performance measurements of Litmus, it is best to disable TRACE() debugging.

-Glenn
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