[Developers] Proposed Cactus Timer API Completion

David Rideout (drideout) drideout at hamilton.edu
Tue Aug 3 17:50:38 CDT 2004


One can use the unit string to decide what the timer value means, along with a convention of what to put in the string.

I think a 64 bit integer makes more sense when counting discrete objects, no?  It has greater precision, since no bits are wasted on the exponent.  At some point it will be impossible to increment the  floating point timer, and this will occur some orders of magnitude before the (same size) integer overflows.

-David

----- Original Message -----
From: Erik Schnetter <schnetter at aei.mpg.de>
Date: Tuesday, August 3, 2004 5:43 pm
Subject: Re: [Developers] Proposed Cactus Timer API Completion

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> On Tuesday 03 August 2004 23:27, David Rideout (drideout) wrote:
> > Isn't there a PAPI thorn which measures all sorts of fun things such
> > as cache misses and integer operations, using the Cactus timer 
> API? 
> > How hard can it be to generalize to measuring things with counters
> > whose physical interpretation may be something other than time?  Why
> > not just carry around a description string and a string for 
> units? 
> 
> A description string is only useful for printing to the user.  If 
> the 
> programme should take any action after measuring an elapsed time, 
> it 
> has to know the unit of the measurement.  For example, if you want 
> to 
> schedule checkpointing is such a manner that it takes no more than 
> 10% 
> of the run time, then it doesn't help you if the timer says that 
> checkpointing took 100.5 units, unless you know the unit.  
> (seconds?  
> milliseconds?  fortnights?  cache misses?)  Therefore I would 
> suggest 
> that the timing unit is always "second", and that the type is 
> either 
> "double" or "CCTK_REAL".
> 
> Incidentally, many events occur so often that 32 bits are not 
> enough to 
> count them.  In this case, the simplest (and portable) solution is 
> to 
> use "double" or "CCTK_REAL" for counts as well.
> 
> - -erik
> 
> - -- 
> Erik Schnetter <schnetter at aei.mpg.de>   
> http://www.aei.mpg.de/~eschnett/
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