[R] flops calculation
tlumley at u.washington.edu
Mon Oct 29 15:49:22 CET 2007
On Sun, 28 Oct 2007, kevinchang wrote:
> Hi all,
> Since proc.time return three different kind of times (user, system and
> elapsed) , I am wondering which one is right for calculating flops.
Probably none of them. The 'user'+'system' time is the amount of CPU time
that can be blamed on R. For most applications this time is mostly not
used in floating point calculations, so it doesn't really seem meaningful
to use it in a denominator and call the result 'flops'.
Sometimes even the 'user'+'system' time is an underestimate of R's
resource use -- for example, indexing a large file in RSQLite takes a long
elapsed time with relatively little user or system time, apparently
because the system is waiting for disk seeks [the disk is being treated as
a random-access device].
Thomas Lumley Assoc. Professor, Biostatistics
tlumley at u.washington.edu University of Washington, Seattle
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