[Rcpp-devel] sugar performance

[Douglas Bates]

On Wed, Dec 22, 2010 at 5:33 AM,  <romain at r-enthusiasts.com> wrote:
>  Hello,
>
> Following Gabor's thread yesterday, I looked into R source code and figure that we don't need to test for NA when using numeric vector. See this:
>
> require(inline)
> require(Rcpp)
>
> pl <- cxxfunction( , '
>    return List::create(
>        NA_REAL + NA_REAL,
>        NA_REAL + 1.0,
>        1.0 + NA_REAL
>        );
> ', plugin = "Rcpp" )
> pl()
>
> As a consequence, I've updated plus.h to skip the tests when dealing with numeric sugar expressions.

Technically I think that you supposed to have code that assumes that
numeric NA's propagate inside a check for

#if  IEEE_754

#endif

The number of systems running R that don't follow the IEEE floating
point standard is vanishingly small but either very old systems
(SPARC/Solaris, I believe, possibly AIX on some esoteric hardware) or
newer architectures (some versions of ARM, various graphics chips
using CUDA and similar systems) might not so it is best to test.

>
>
> Also, I'm trying to write the looping internally in order to get a better comparison. With the attached file, I get:
>
> romain@ /tmp $ Rscript gab.R
> Le chargement a nécessité le package : inline
> Le chargement a nécessité le package : methods
> Le chargement a nécessité le package : Rcpp
> Le chargement a nécessité le package : rbenchmark
>   test replications elapsed relative user.self sys.self user.child sys.child
> 1 sugar            1   0.002      1.0     0.001        0          0         0
> 2     R            1   0.005      2.5     0.004        0          0         0
>   test replications elapsed relative user.self sys.self user.child sys.child
> 1 sugar            1   0.035      1.0     0.034    0.000          0         0
> 2     R            1   0.049      1.4     0.049    0.001          0         0
>   test replications elapsed relative user.self sys.self user.child sys.child
> 1 sugar            1   4.699 1.000000     3.701    0.999          0         0
> 2     R            1   5.324 1.133007     4.267    1.056          0         0
>   test replications elapsed relative user.self sys.self user.child sys.child
> 2     R            1  45.995 1.000000    39.076    6.911          0         0
> 1 sugar            1  61.249 1.331645    46.178   15.067          0         0
>
>
> Another contributor to the time difference is the handling of garbage collection. Each time the constructor of an Rcpp class is called, a call to R_PreserveObject is issued. And each time the destructor is called, R_ReleaseObject is called. In this R-devel thread last year:
> http://thread.gmane.org/gmane.comp.lang.r.devel/23167 , some inefficiency of these functions were revealed, with a patch from Simon, but this has not been incorporated into R yet.
>
> Maybe we can send a reminder to sponsor the patch or use something else in Rcpp instead.
>
>
> The benchmark shows that sugar beats R first, and then R gets better as the size of the vectors grow. I think this is related to loop unrolling. it seems that it gives good performance for smaller lengths and not as good for bigger lengths.
>
>
> Romain
>
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