mpid_wtime.tex

刚才是说明 现在是安装程序在 LINUX环境下进行编程的MPICH安装文件

\startmanpage
\mantitle{MPID{\tt \char`\_}Wtime}{tex}{10/7/2002}
\manname{MPID{\tt \char`\_}Wtime}
--- Return a time stamp 
\subhead{Synopsis}
\startvb\begin{verbatim}
void MPID_Wtime( MPID_Wtime_t *timeval )

\end{verbatim}
\endvb

\subhead{Output Parameter}
\startarg{timeval }{A pointer to an {\tt MPID{\tt \char`\_}Wtime{\tt \char`\_}t} variable.
}
\par
\subhead{Notes}
This routine returns an {\em opaque} time value.  This difference between two
time values returned by {\tt MPID{\tt \char`\_}Wtime} can be converted into an elapsed time
in seconds with the routine {\tt MPID{\tt \char`\_}Wtime{\tt \char`\_}diff}.
\par
This routine is defined this way to simplify its implementation as a macro.
For example, for Intel x86 and gcc,
\begin{verbatim}
#define MPID_Wtime(timeval) \
  __asm__ volatile (".byte 0x0f, 0x31" : "=A" (*timeval))
\end{verbatim}

\par
For some purposes, it is important
that the timer calls change the timing of the code as little as possible.
This form of a timer routine provides for a very fast timer that has
minimal impact on the rest of the code.
\par
From a semantic standpoint, this format emphasizes that any particular
timer value has no meaning; only the difference between two values is
meaningful.
\par
\subhead{Module}
Timer
\par
\subhead{Question}
MPI-2 allows {\tt MPI{\tt \char`\_}Wtime} to be a macro.  We should make that easy; this
version does not accomplish that.
\endmanpage