Re: [Xenomai] BeagleBone Xenomai Latency

[Charles Steinkuehler <charles@steinkuehler.net>]

On 1/12/2014 2:56 PM, Gilles Chanteperdrix wrote:
> On 01/11/2014 09:58 PM, Charles Steinkuehler wrote:
>> (Starting a new thread)
>> On 1/7/2014 5:13 PM, Gilles Chanteperdrix wrote:
>>> On 01/07/2014 11:55 PM, Charles Steinkuehler wrote:
>>>> On 1/7/2014 4:47 PM, Gilles Chanteperdrix wrote:
>>>>> Is there any chance you could trigger a trace with the I-pipe 
>>>>> tracer?
>>>
>>>> I can try...give me a while to sort through the I-pipe:Tracer wiki
>>>> page (or are there better instructions?).
>>>
>>> Enable I-pipe tracer in kernel configuration, especially
>>> IPIPE_TRACE_MCOUNT, and IPIPE_TRACE_VMALLOC.
>>>
>>> When the system has booted, do:
>>>
>>> echo 1 > /proc/ipipe/trace/enable
>>> echo 1000 > /proc/ipipe/trace/back_trace_points
>>>
>>> Then launch latency -p 200 -f
>>>
>>> Run the load you usually run (for instance dohell).
>>>
>>> When the test is finished, do
>>> cat /proc/ipipe/trace/frozen > /tmp/frozen.txt
>>>
>>> then post the resulting frozen.txt to this list.
>>>
>>> Expect the latency found by the test to be double the latency you get
>>> without the I-pipe tracer.
>>
>> OK, I tested a variety of kernels.  Simply enabling the ipipe trace
>> options on the otherwise unchanged kernel configuration I'm using
>> resulted in a system that was *EXTREMELY* slow and unresponsive, even
>> before I enabled the iPipe trace.  After waiting the better part of a
>> day for a GUI application to launch, I gave up on this kernel and tested
>> one with the recommended performance options:
>>
>>
>> Already in the BeagleBone Xenomai kernels I've been building:
>>> optimize for size
>>> disable CONFIG_PREEMPT
>>> enable stack unwinding
>>> disable root thread priority coupling (xenomai option)
> 
> The .config you attached to the mail I am answering has CONFIG_PREEMPT
> enabled.
> You may want to select CONFIG_PREEMPT_NONE.

OK, thanks for the clarification.  I show CONFIG_PREEMPT was not set,
but CONFIG_PREEMPT_VOLUNTARY was:

# CONFIG_PREEMPT_NONE is not set
CONFIG_PREEMPT_VOLUNTARY=y
# CONFIG_PREEMPT is not set

I can select CONFIG_PREEMPT_NONE and re-test.

> I also do not really understand the trace you have attached. Are you
> running other real-time tasks than the latency test? Because to get
> accurate results, you should run the latency test without any other
> programs using xenomai.

Yes, my primary load is running LinuxCNC, which uses Xenomai.  I'll
build a new kernel and post a new trace, this time without running any
other programs that use Xenomai.

Thanks for all the advice and help!

-- 
Charles Steinkuehler
charles@steinkuehler.net

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