[IPython-dev] Feature request/how?

Fernando Perez Fernando.Perez at colorado.edu
Tue Feb 22 15:32:33 CST 2005


Ville Vainio wrote:
> On Tue, 2005-02-22 at 12:05 -0700, Fernando.Perez at colorado.edu wrote:
> 
> 
>>This is expected: the code I gave you uses genutils.clock(), which is written
>>(at least on Unix) to report only true CPU time.  A sleep() call doesn't
>>consume almost any cpu time at all.  Feel free to make a modified version of
>>this function which uses other timing routines from the time module if you want
>>wall clock time.  As far as I'm concerned, reporting wall clock time is in most
>>cases a bug, since it's completely context dependent.  But there are valid
>>cases for wanting it, so you could for example add a -w switch to this function
>>to use a wall clock instead.
> 
> 
> I'd be tempted to think that wall clock time should be the default.
> Isn't CPU time quite arbitrary measurement if the problem is I/O bound?
> timeit module also measures wallclock time (using time.time() on posix).
> 
> Knowing the wallclock time is also necessary to see whether the solution
> under experimentation will fly in a real application. It's hard to get
> an intuitive grasp from CPU time.

Well, I guess we just come from different backgrounds.  For me, cpu time is 
pretty much the only relevant number 99% of the time, but that's because I 
work in scientific computing problems which are not I/O bound.  For others, 
wall time may be what matters (I said as much above: "As far as I'm concerned, 
reporting wall clock time is in most cases a bug", note the _I_ in that quote).

I am unfortunately completely swamped right now, and can't afford to write a 
nice, generic, flexible timing magic which can address all valid usage cases. 
  If anyone volunteers a patch, I'll gladly include it (it's not hard). 
Otherwise, the basic, cpu-bound %time I wrote stays.  As is, it will be quite 
useful to scientific computing types (my most significant target market).

Regards,

f




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