[ag-automation] echo 1 > /sys/kernel/debug/tracing/latency_hist/enable/preemptirqsoff causes crash

[Carsten Emde]

Matthias,

>> Did you forget to disable sleep states?
>>
>> This is best done by writing "0" to /dev/cpu_dma_latency such as
>>
>> int fd = open("/dev/cpu_dma_latency", O_WRONLY);
>> if (fd >= 0)
>>     write(fd, "0", 1);
>> /* do not close fd */
>
> Yes, I did that. lsof confirmed.
Hmm, then the next step probably is to implement something similar to 
cyclictest's break trace command in your application:
1. Start function tracing
2. Run your application
3. If your application detects the increased latency -> write "0" to 
/sys/kernel/debug/tracing/tracing_on
4. Analyze the trace

	-Carsten.