For etime, the elapsed time is:
Single Processor Execution—CPU time for the calling process
Multiple Processor Execution—wallclock time while processing your program
The runtime library determines that a program is executing in a multiprocessor mode if either the PARALLEL or OMP_NUM_THREADS environment variables are defined to some integer value greater than 1.
The function is called by:
e = etime( tarray ) |
|||
tarray |
real(2) |
Output |
e= -1.0: Error: tarray values are undefined. e≠ -1.0: Single Processor: User time in tarray(1). System time in tarray(2) Multiple Processor: Wall clock time in tarray(1), 0.0 in tarray(2) |
Return value |
real |
Output |
e= -1.0: Error e≠ -1.0: The sum of tarray(1) and tarray(2) |
Take note that the initial call to etime will be inaccurate. It merely enables the system clock. Do not use the value returned by the initial call to etime.
Example: etime(), single processor:
demo% cat tetime.f real e, etime, t(2) e = etime(t) ! Startup etime - do not use result do i = 1, 10000 k=k+1 end do e = etime( t ) print *, ’elapsed:’, e, ’, user:’, t(1), ’, sys:’, t(2) end demo% f95 tetime.f demo% a.out elapsed: 0.02 , user: 0.01 , sys: 0.01 demo% |
See also times(2), and the Fortran Programming Guide.