On Wed, 20 Apr 2005, Peter Dalgaard wrote:
Luke Tierney <[EMAIL PROTECTED]> writes:
Vectorized operations in R are also as fast as compiled C (because that is what they are :-)). A compiler such as the one I'm working on will be able to make most difference for non-vectorizable or not very vectorizable code. It may also be able to reduce the need for intermediate allocations in vectorizable code, which may have other benefits beyond just speed improvements.
Actually, it has struck me a couple of times that these operations are not as fast as they could be, since they are outside the scope of fast BLAS routines, but "embarrassingly parallel" code could easily be written for the relevant hardware. Even on uniprocessor systems there might be speedups that the C compiler cannot find (e.g. because it cannot assume that source and destination of the operation are distinct).
My guess is that for anything beyond basic operations we are doing OK on uniprocessors. but it would be useful to do some testing to be sure. For the basic operations I suspect we are paying a heavy price for the way we handle recycling, both in terms of overhead as such and in terms of inhibiting compiler optimizations. For performance it would probably be better to code the scalar-vector, equal-length-vector, and general cases separately, though keeping the code maintainable may be a bit of a challenge. Again testing on a range of platforms and compilers would be useful.
With multiprocessors likely to become more widely available it would be good to look into ways of factoring the vectorized math code so we can slide in one that uses threads when approprate. This should dovetail nicely with compilation to identify larger vectorized expressions that can be parallelized as a unit; I hope to look into this a bit this summer.
luke
-- Luke Tierney Chair, Statistics and Actuarial Science Ralph E. Wareham Professor of Mathematical Sciences University of Iowa Phone: 319-335-3386 Department of Statistics and Fax: 319-335-3017 Actuarial Science 241 Schaeffer Hall email: [EMAIL PROTECTED] Iowa City, IA 52242 WWW: http://www.stat.uiowa.edu
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