[Rcpp-devel] New self-contained OpenMP example (Was: Stack imbalance warning when using Rcpp and OpenMP)

[Dirk Eddelbuettel]

On 26 August 2011 at 08:37, Davor Cubranic wrote:
| On August 25, 2011 05:32:45 PM Dirk Eddelbuettel wrote:
| > Long story short I just committed a new self-contained example to the Rcpp
| > source which you can look at (and copy) via the URL
| [...]
| > The results bear this out. On my (standard i7, four cores hyperthreaded)
| > box:
| > 
| > edd at max:~$ r ~/svn/rcpp/pkg/Rcpp/inst/examples/OpenMP/OpenMPandInline.r
| > Loading required package: methods
| >               test replications elapsed relative user.self sys.self
| > 2     funOpenMP(z)          100   3.219 1.000000     25.26     0.07
| > 3 funSerialRcpp(z)          100   9.030 2.805219      9.43     0.32
| > 4  funSugarRcpp(z)          100   9.423 2.927307      9.06     0.35
| > 1     funSerial(z)          100   9.601 2.982603      9.59     0.00
| > edd at max:~$
| > 
| [...]
| > Rcpp sugar has no real leg up on manual loops, but is the shortest
| > implementation in two lines. Looping over an Rcpp vector is a little faster
| > than looping over a C++ STL vector (which incurs a copy).
| 
| I know you wanted to keep all code looking the same, but with std::transform 
| all serial code is very short:

Good thinking, I'll make that change!

| serialStdAlgCode <- '
|    std::vector<double> x = Rcpp::as<std::vector< double > >(xs);
|    std::transform(x.begin(), x.end(), x.begin(), ::log);
|    return Rcpp::wrap(x);
| '
| funSerialStdAlg <- cxxfunction(signature(xs="numeric"), body=serialStdAlgCode, 
| plugin="Rcpp")
| 
| serialStdAlgRcppCode <- '
|    Rcpp::NumericVector x = Rcpp::NumericVector(xs);
|    std::transform(x.begin(), x.end(), x.begin(), ::log);
|    return x;
| '
| funSerialStdAlgRcpp <- cxxfunction(signature(xs="numeric"), 
| body=serialStdAlgRcppCode, plugin="Rcpp")

That's much nicer. And quicker. Nice :)
 
| The results (without OpenMP because I'm currently on a single-core CPU):
| 
|                     test replications elapsed relative user.self sys.self
| 3 funSerialStdAlgRcpp(z)           20   4.236 1.000000     3.792    0.252
| 4       funSerialRcpp(z)           20   4.312 1.017941     3.792    0.272
| 5        funSugarRcpp(z)           20   4.537 1.071058     3.744    0.588
| 2     funSerialStdAlg(z)           20   5.514 1.301700     4.329    0.884
| 1           funSerial(z)           20   5.536 1.306893     4.480    0.808


Thanks for the suggestion.

Dirk

-- 
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New York (Sep 24) and San Francisco (Oct 8), more details are at
http://dirk.eddelbuettel.com/blog/2011/08/04#rcpp_classes_2011-09_and_2011-10
http://www.revolutionanalytics.com/products/training/public/rcpp-master-class.php