[R] system.time

Prof Brian Ripley ripley at stats.ox.ac.uk
Mon Jul 23 14:59:31 CEST 2001

On Mon, 23 Jul 2001, Agustin Lobo wrote:

> The manual entry for system.time refers to
>  "user, system, and total elapsed times for the currently running R
> process".
> Is user time the time spent by the process itself and system time the
> time spent on other system activities?

These are reported by your (presumably Unix?) system.  Most likely both
times are spent by the R process, the `user' time in the user code space,
and the `system' time in kernel calls.

Look up the times system call on your system for the exact details.
For example, Solaris says

     The tms_utime member is the CPU time  used  while  executing
     instructions in the user space of the calling process.

     The tms_stime member is the CPU time used by the  system  on
     behalf of the calling process.

On Unix-alikes, system.time calls proc.time whose C code calls times.

Brian D. Ripley,                  ripley at 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 272860 (secr)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595

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