[fpc-devel] High performance Linux timer

[Graeme Geldenhuys]

Felipe Monteiro de Carvalho wrote:
> I once implemented a high precision timer on linux, but I don't
> remember how I did it. Look at the code here:
> 
> http://wiki.lazarus.freepascal.org/EpikTimer
> 

Thanks, I'll have a look at the code for more details. From the wiki, it 
sounds like there might be some issues EpikTimer implementation though.

  * .... Timestamp Counter.
  * Pentium IV 3,2Mhz on Windows and Linux with great precision (~ 
3,220,000,000 ticks per second)


Timestamp counter from the CPU (assuming we are speaking of RDTSC) is 
susceptible to many issue. eg: A Intel P4 3.2Mhz does not always produce 
3,220,000,000 ticks per second. Powersaving features like SpeedStep, 
Hibernate etc all affect the CPU clock speed. Also on a multi-core 
system, not all cores are guaranteed to run at the same clock speed.

Above information was gathered from the WikiPedia article.
   http://en.wikipedia.org/wiki/Rdtsc

Anybody know what Win32's QueryPerformanceCounter() uses internally to 
get a stable timer?  Or is QueryPerformanceCounter also susceptible to 
powersaving features?


Regards,
   - Graeme -


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