PCSAMPLE(2) System Calls PCSAMPLE(2)
NAME
pcsample - program execution time profile
SYNOPSIS
#include <pcsample.h>
long pcsample(
uintptr_t samples[],
long nsamples);
DESCRIPTION
The
pcsample() function provides CPU-use statistics by profiling the
amount of
CPU time expended by a program.
For profiling dynamically-linked programs and 64-bit programs, it is
superior to the
profil(2) function, which assumes that the entire program
is contained in a small, contiguous segment of the address space, divides
this segment into "bins", and on each clock tick increments the counter
in the bin where the program is currently executing. With shared
libraries creating discontinuous program segments spread throughout the
address space, and with 64-bit address spaces so large that the size of
"bins" would be measured in megabytes, the
profil() function is of
limited value.
The
pcsample() function is passed an array
samples containing
nsamples pointer-sized elements. During program execution, the kernel samples the
program counter of the process, storing unadulterated values in the array
on each clock tick. The kernel stops writing to the array when it is
full, which occurs after
nsamples /
HZ seconds of process virtual time.
The
HZ value is obtained by invoking the call
sysconf(_SC_CLK_TCK). See
sysconf(3C).
The sampling can be stopped by a subsequent call to
pcsample() with the
nsamples argument set to 0. Like
profil(), sampling continues across a
call to
fork(2), but is disabled by a call to one of the
exec family of
functions (see
exec(2)). It is also disabled if an update of the
samples[] array causes a memory fault.
RETURN VALUES
The
pcsample() function always returns
0 the first time it is called. On
subsequent calls, it returns the number of samples that were stored
during the previous invocation. If
nsamples is invalid, it returns
-1 and
sets
errno to indicate the error.
ERRORS
The
pcsample() function will fail if:
EINVAL The value of
nsamples is not valid.
ATTRIBUTES
See
attributes(7) for descriptions of the following attributes:
+--------------------+-------------------+
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
+--------------------+-------------------+
|MT-Level | Async-Signal-Safe |
+--------------------+-------------------+
|Interface Stability | Stable |
+--------------------+-------------------+
SEE ALSO
exec(2),
fork(2),
profil(2),
sysconf(3C),
attributes(7) March 10, 1998
PCSAMPLE(2)