request: allow inline functions in R
On Fri, 14 May 2004, Li Long wrote:
Hi, R core developers, I work in the Swiss Institute of Bioinformatics. We have two clusters of Intel Itanium2 clusters for bioinformaticians to crank their data. One piece of software they use heavily is R and BioConductors. I ported the R codes and R packages to this platform already, and am working on optimizing their performance. I'm using Intel C/C++ compiler on this platform running Linux. One of my findings is that turning some functions in R to "inline" functions boost performance significantly. While R follows strict C89 standard right now, there're quite some good reasons to relax the rule somewhat. From my experience in software development in industry, I understand very well both the portability issue and backward compatability issue, I also see the hidden cost of holding back for too long and not fully achieving the potential of new technology,
Could you then please quantify that hidden cost?
I recommend that we allow "inline" functions in R's C codes.
In what sense do `we' not allow it? And who is `we'? The problem is that very few compilers fully support C99, and others have different ways to indicate inlining. So a configure test is needed. I am sure that if you provide one together with patches to parts of the code where you find inlining beneficial, the real `we' would consider it carefully. Especially if the `hidden cost' is noticeable. ....
In R, there are quite some simple functions that are called extremely often, such as "R_IsNaNorNA", "R_finite", etc. They are used in heavy loops quite a lot. They disrupt the pipelining, and negatively affect the performance of the software. For instance, on IA64, system call of "isnan" cost 4 cycles, while a wrapper like "R_IsNaNorNA" could cost several times more.
However, one of the motivations of eliminating support for non-IEEE-754 platforms in R 2.0.0 is to enable some of this baggage to be eliminated. But the wrapper is there for a good reason: to get the right answer. Since I gather you have suitably modified code, it would be helpful to your case to provide data - on real problems - on a mainstream platform. of the actual performance impact of not inlining.
Brian D. Ripley, ripley@stats.ox.ac.uk Professor of Applied Statistics, http://www.stats.ox.ac.uk/~ripley/ University of Oxford, Tel: +44 1865 272861 (self) 1 South Parks Road, +44 1865 272866 (PA) Oxford OX1 3TG, UK Fax: +44 1865 272595