[R] Huge difference btw system time and elapsed time

[Martin Maechler]

>>>>> "LS" == Libo Sun <libosun at rams.colostate.edu>
>>>>>     on Tue, 21 Feb 2012 21:09:54 -0700 writes:

    > Thanks. Shall I sum the user time and system time, which
    > roughly equals to the elapsed time?

No.  Rather just use the  user time,
i.e.  proc.time()[[1]]   
    system.time()[[1]]   etc

That's typically good enough [as long as you don't use
internally multithreaded BLAS, or  parallelize / distribute your job,
or other things you won't be doing (yet)].

Martin Maechler, ETH Zurich

   > I also tried to improve the code by using 'cmpfun(myfunction)' in
   > 'compiler' package, however, it doesn't help too much.

   > Libo

> On Tue, Feb 21, 2012 at 8:11 PM, R. Michael Weylandt <
> michael.weylandt at gmail.com> wrote:

> The time relationships aren't strictly linear between any of the three
> measures, but *very generally* I've interpreted them as something
> like:
>
> User: stuff you do (i.e., doing all the commands)
> System: stuff at the OS level (memory allocations and whatnot)
> Elapsed: Clock time
>
> None is a great measure in isolation, but the system time is not the
> worrisome one here: it looks like your script takes about a day and a
> half to run....that might be ok (and perhaps unavoidable) but it looks
> like there might be value in trying to squeeze some speed out of your
> script. A simple thing like byte-compiling that gives 2x speedup would
> be huge here.
>
> Michael
>
> On Tue, Feb 21, 2012 at 10:06 PM, Libo Sun <libosun at rams.colostate.edu>
> wrote:
> > Hi all,
> >
> > I got this time for my code,
> >
> >> proc.time()-pt
> >      user     system    elapsed
> > 132541.743      0.004 132533.526
> >
> > As you can see, there is huge difference btw elapsed time and system
> time.
> > Does that mean lots of I/O? Or some bad coding?
> >
> > Thanks,
> > Libo