CPU time, elapsed time, multiple processors and time measurements

[rase]

Now and then we have discussions here in the forum about CPU time, elapsed time, with single or multiple threads, and the intricacies of time measurements using functions and subroutines provided by IVF and Windows. Although I use time-measuring functions for a number of years now, I am not always sure what I get from the functions and subroutines in fact. Could Dr Fortran perhaps be so kind to write a tutorial about the subject, sharing his encyclopedic knowledge about the subject with us?

[SergeyKostrov]

There is a very short description for CPU_TIME function in another thread: Forum Topic: CPU time vs. time Web-link: software.intel.com/en-us/forums/topic/392280 Note: Take a look at first a couple of posts. Thanks.

[Bernard]

What dll CPU_TIME belongs to?Does anybody know?

[SergeyKostrov]

>>...What dll CPU_TIME belongs to? Does anybody know? This is Not a DLL. This is a Fortran function and take a look at online help for more information.

[Bernard]

This is compiler intrinsic function.I was interested more in implementation.What timer this function accesses.

[SergeyKostrov]

You were told many times in the past that Intel doesn't release that information, that is implementation details.

[Bernard]

Sorry sometimes in the heat of discussion you can easily forgot such a things.

[SergeyKostrov]

You could try to find Open Source Fortran and take a look at sources of CPU_TIME function ( of course if it is supported and implemented ).

[Bernard]

Thanks Sergey.

[TimP]

One of the more recent discussions about ifort windows timers: http://software.intel.com/en-us/forums/topic/277492

It's true there is more open discussion relative to gfortran on Windows, and it was agreed recently that improvements are needed there.

[Bernard]

By looking at mentioned by Tim article it is clear that CPU_TIME on Win platform can use one of the RTC available.It is my theory that for example on Win platform CPU_time can call indirectly one of the Hal timing functions.

[Steven_L_Intel1]

Thanks for the article suggestion - I'll keep it in mind.

[SergeyKostrov]

Please take a look at: Forum Topic: Precision of CPU_Time and System_Clock Web-link: software.intel.com/en-us/forums/topic/277492