[LITMUS^RT] Feather Trace Tool in LITMUS-RT

[Björn Brandenburg]

Hi John,

what Felipe points out is correct: st_trace only traces real-time tasks. However, launching the script with rt_launch will not work because shell scripts fork of new processes, and real-time status is not inherited across a fork in LITMUS^RT.

If you are looking for a dummy workload to test your tracing setup, checkout rtspin in liblitmus. If you want to script task behavior for testing purposes, use Python, Perl, Lua, or some other scripting language that runs its interpreter as a single process (and launch the interpreter with rt_launch).

- Björn

On 13.11.2013, at 09:28, Felipe Cerqueira <felipeqcerqueira at gmail.com> wrote:

> Hi John,
> 
> st_trace only traces task events such as releases, deadlines and context-switches of real-time jobs.
> For it to work with the bash script, you need to launch your program with rt_launch, found in liblitmus folder.
> Otherwise the process will be considered a best-effort task and will not show up in the scheduling trace.
> 
> Thanks,
> Felipe
> 
> 
> 2013/11/13 Litmus ForLinux <litmustiger at gmail.com>
>> Hi,
>> 
>> I am a novice in Linux Kernel coding and I have found LITMUS to be interesting. I compiled and installed LITMUS-RT in my Linux (Ubuntu 12.04) as per the instructions given in the LITMUS website. Also I compiled feather trace tool in my LITMUS system.(including LIBLITMUS dependencies).
>> 
>> How to use feather tool and trace the process (by its release and execution time) using the litmus logs. I execute a background process and tried to trace the process using feather tool. Following are the steps : 
>> 
>> 1. I wrote following shell script  (task.sh)-
>>     ls 
>>     sleep 20
>>     ls
>>     sleep 20
>> 
>> Then I executed the script in the background  - sh  task.sh &
>> 2. Once the process starts to run in the background, I executed st_trace immediately.
>> 3. Trace tool starts executing and it gives a message - 
>> "Press Enter to end tracing" 
>> I pressed enter after some time and got following - 
>> "Disabling 10 events .... /dev/litmus_sched_trace1: 0 bytes read."
>> 
>> Because of this, are no contents inside the log file. If I try to execute some other task as mentioned in the feather trace tool documentation, "./st_trace global-exp" I encounter same "0 bytes read" message. 
>> 
>> Please help me to resolve this issue. I want to have to log file generated.
>> 
>> Thanks
>> John
>> 
>> 
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> 
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