Re: Posix Execution time clock

[Hector Perez Tijero <perezh@unican.es>]

Hi all,

Just to complete the info. I have repeated a similar test (SMP and 
scaling frequency disabled in the BIOS, TSC clock) with another function:

If I measure the attached function with CLOCK_THREAD_CPUTIME_ID, I keep 
getting variable timing results. The execution of this function takes 
about 400 usecs in my system. Having called it more than 10_000 times, 
most of the measures are within 100 usecs from this value. This range 
makes sense to me. But I have found a few measures (less than 10 out of 
10_000) which are over 1100 usecs, which it's a bit suspicious. Since 
this clock just takes the execution time associated to a single thread 
(no preemption time should be included) and the function's execution 
time could be considered as "constant", it seems that something is going 
wrong with this kind of clock.

Any idea?

Thanks

Hector

PS: Ubuntu 2.6.24.-25-rt is based on 2.6.24.7-rt27 patch (link 
<http://packages.ubuntu.com/hardy-updates/linux-restricted-modules-2.6.24-25-rt>)

void make_job ()
{
  long temp = 0;
  int index, index2 = 0;
  for (index = 0; index < 5000; index ++) {
     temp += index;
     if (index%97 == 0) {
       for (index2 = 0; index2 < 1000; index2 ++) {
          temp +=index;
       }
     }
  }
}

Uwe Kleine-König escribió:
> On Tue, Dec 01, 2009 at 10:32:28AM -0200, Luis Claudio R. Goncalves wrote:
>   
>> Along with that, the latest version for 2.6.24, IIRC, was 2.6.24.7-rt27.
>> So, it sounds like you are using older versions of old software.
>>     
> The version scheme of Ubuntu doesn't allow to read the used rt patch
> from the kernel version.  The Ubuntu version used is 2.6.24-25-rt.  This
> only means something like:  The 25th Ubuntu revision of the 2.6.24
> kernel in the rt feature set.
>
> Best regards
> Uwe
>
>   
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