On 02/29/2012 08:44 PM, Charles Lesire-Cabaniols wrote:
> 2012/2/29 Gilles Chanteperdrix <[email protected]>
>
>> On 02/29/2012 07:03 PM, Charles Lesire-Cabaniols wrote:
>>> 2012/2/29 Gilles Chanteperdrix <[email protected]>
>>>
>>>> On 02/29/2012 06:52 PM, Charles Lesire-Cabaniols wrote:
>>>>> 2012/2/29 Gilles Chanteperdrix <[email protected]>
>>>>>
>>>>>> On 02/29/2012 06:29 PM, Charles Lesire-Cabaniols wrote:
>>>>>>> Hi guys,
>>>>>>>
>>>>>>> I have installed a Debian+Xenomai (2.6.0) OS on my Gumstix Overo.
>>>>>>>
>>>>>>> I want to evaluate the execution time of a simple program, executed
>> as
>>>> a
>>>>>>> real-time thread.
>>>>>>>
>>>>>>> I definitely wonder about which functions to use, as I have
>> completely
>>>>>>> inconsistent measures.
>>>>>>> I have tried using rt_timer_read, rt_timer_tsc, clock_gettime.
>>>>>>> I also directly read the CNNT register with ARM instructions (which
>> is
>>>>>> the
>>>>>>> only one I think correct) in order to have a (good?) reference.
>>>>>>> (...)
>>>>>>> What am I doing wrong?
>>>>>>
>>>>>> So, you should printf("%Lu %Lu\n", rt_timer_read(), rt_timer_tsc());
>>>>>>
>>>>>> Not printf("%lu", ...)
>>>>>>
>>>>>> --
>>>>>> Gilles.
>>>>>>
>>>>>
>>>>> Effectively, that looks cleaner, thanks:
>>>>>
>>>>> ----- Xenomai rt_timer_read -----
>>>>> start: 49166276042 ; end: 49166432273 ; (s-e): 156231 ; CET: 156231
>>>>> ----- Xenomai rt_timer_tsc -----
>>>>> start: 639161547 ; end: 639163539 ; (s-e): 1992 ; CET: 1992
>>>>> ----- Xenomai clock_gettime -----
>>>>> [ s] start: 946684855 ; end: 946684855 ; (s-e): 0 ; CET: 0
>>>>> [ns] start: 275520245 ; end: 275677089 ; (s-e): 156844 ; CET: 156844
>>>>>
>>>>> My ARM instruction reads 110554.
>>>>>
>>>>> Which Xenomai function should I use?
>>>>> Which one is supposed to be the more accurate?
>>>>> Does rt_timer_read return nsecs?
>>>>> What is the unit of rt_timer_tsc?
>>>>
>>>> rt_timer_tsc uses whatever hardware counter is available, you need
>>>> rt_timer_tsc2ns or rt_timer_ns2tsc to convert between this unit to and
>>>> from nanoseconds.
>>>>
>>>> For more details, see:
>>>>
>>>>
>>>>
>> http://www.xenomai.org/documentation/xenomai-2.6/html/api/group__native__timer.html
>>>>
>>>> Depending on how xenomai user-space was compiled, rt_timer_tsc should
>>>> have the lowest overhead.
>>>>
>>>
>>> And are the default options the best ones?
>>
>> Yes, but I am not sure the debian package uses the default one. Please
>> post here the disassembly of rt_timer_tsc, I will tell you if your
>> system is compiled for the lowest overhead.
>>
>>
> How to do that?
arm-none-linux-objdump -d /path/to/libnative.so.3 | less
search <rt_timer_tsc>, when you find it, post the disassembly here.
>
>
>>> How can I tune the TSC performance?
>>
>> You use the --enable-arm-tsc or --disable-arm-tsc option of xenomai
>> configure script. The default is --enable-arm-tsc=kuser and should be
>> the best option. If you pass --disable-arm-tsc, rt_timer_tsc will emit a
>> system call.
>>
>>
> I do not use the debian package, but I compile Xenomai from sources ;
> actually I have a vanilla kernel and a debain rootfs.
> I think --enable-arm-tsc is the default then.
Yes.
--
Gilles.
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