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Date: Wed, 29 Feb 2012 19:01:48 +0100
From: Gilles Chanteperdrix <gilles.chanteperdrix@xenomai.org>
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Subject: Re: [Xenomai-help] Execution time profiling
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To: Charles Lesire-Cabaniols <charles.lesire@domain.hid>
Cc: xenomai@xenomai.org

On 02/29/2012 06:52 PM, Charles Lesire-Cabaniols wrote:
> 2012/2/29 Gilles Chanteperdrix <gilles.chanteperdrix@xenomai.org>
> 
>> 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.

-- 
					    Gilles.