pcsample - program execution time profile
long pcsample(uintptr_t samples, long nsamples);
The pcsample() function provides CPU-use statistics by pro-
filing the amount of CPU time expended by a program.
For profiling dynamically-linked programs and 64-bit pro-
grams, 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 seg-
ment 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 seg-
ments 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
The pcsample() function is passed an array samples contain-
ing nsamples pointer-sized elements. During program execu-
tion, 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 pcsam-
ple() 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 indi-
cate the error.
The pcsample() function will fail if:
The value of nsamples is not valid.
See attributes(5) for descriptions of the following attri-
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
| MT-Level | Async-Signal-Safe |
| Interface Stability | Stable |
exec(2), fork(2), profil(2), sysconf(3C), attributes(5)
Man(1) output converted with