PCSAMPLE(2) System Calls PCSAMPLE(2)


pcsample - program execution time profile


#include <pcsample.h>

long pcsample(uintptr_t samples[], long nsamples);


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

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.


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.


The pcsample() function will fail if:

The value of nsamples is not valid.


See attributes(7) for descriptions of the following attributes:

|MT-Level | Async-Signal-Safe |
|Interface Stability | Stable |


exec(2), fork(2), profil(2), sysconf(3C), attributes(7)

March 10, 1998 PCSAMPLE(2)