profil.2

<B>Digital的Unix操作系统VAX 4.2源码</B>

.\" SCCSID: @(#)profil.2	8.3	1/28/91
.TH profil 2
.SH Name
profil \- execution time profile
.SH Syntax
.nf
.B void profil(buff, bufsiz, offset, scale)
.B char *buff;
.B int bufsiz, offset, scale;
.fi
.SH Description
.NXR "profil system call"
.NXR "execution time" "profiling"
The
.I buff
points to an area of core whose length (in bytes) is given by
.IR bufsiz .
After this call, the user's program counter (pc)
is examined each clock tick (on RISC machines, 4 milliseconds; on VAX
machines, 10 milliseconds);
.I offset
is subtracted from the pc, and the result is multiplied by
.IR scale .
If the resulting number corresponds to a word
inside
.I buff,
that word is incremented.
.PP
The scale is interpreted as an unsigned,
fixed-point fraction with binary point at the
left: 0x10000 gives a 1-1 mapping of program counter's to words
in
.I buff;
0x8000 maps each pair of instruction words
together.
0x2 maps all instructions onto the beginning of
.I buff,
producing a non-interrupting core clock.
.PP
Profiling is turned off by giving a
.I scale
of 0 or 1.
It is rendered
ineffective by giving a
.I bufsiz
of 0.
Profiling is turned off when an
.I execve
is executed, but remains on in both child and parent 
after a
.IR fork .
Profiling is turned off if an update in
.I buff
would cause a memory fault.
.SH See Also
gprof(1) (for VAX only), setitimer(2), monitor(3)