Tribblix: manual page: pcsample.2

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.