SunOS man pages : profil (2)
System Calls profil(2)
NAME
profil - execution time profile
SYNOPSIS
#include <unistd.h>
void profil(unsigned short *buff, unsigned int bufsiz,
unsigned int offset, unsigned int scale);
DESCRIPTION
The profil() function provides CPU-use statistics by profil-
ing the amount of CPU time expended by a program. The pro-
fil() function generates the statistics by creating an exe-
cution histogram for a current process. The histogram is
defined for a specific region of program code to be pro-
filed, and the identified region is logically broken up into
a set of equal size subdivisions, each of which corresponds
to a count in the histogram. With each clock tick, the
current subdivision is identified and its corresponding his-
togram count is incremented. These counts establish a rela-
tive measure of how much time is being spent in each code
subdivision. The resulting histogram counts for a profiled
region can be used to identify those functions that consume
a disproportionately high percentage of CPU time.
The buff argument is a buffer of bufsiz bytes in which the
histogram counts are stored in an array of unsigned short
int.
The offset, scale, and bufsiz arguments specify the region
to be profiled.
The offset argument is effectively the start address of the
region to be profiled.
The scale argument is a contraction factor that indicates
how much smaller the histogram buffer is than the region to
be profiled. More precisely, scale is interpreted as an
unsigned 16-bit fixed-point fraction with the decimal point
implied on the left. Its value is the reciprocal of the
number of bytes in a subdivision, per byte of histogram
buffer. Since there are two bytes per histogram counter, the
effective ratio of subdivision bytes per counter is one half
the scale.
The values of scale are as follows:
o the maximum value of scale, 0xffff (approximately 1),
maps subdivisions 2 bytes long to each counter.
o the minimum value of scale (for which profiling is
performed), 0x0002 (1/32,768), maps subdivision 65,536
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System Calls profil(2)
bytes long to each counter.
o the default value of scale (currently used by cc
-qp), 0x4000, maps subdivisions 8 bytes long to each
counter.
The values are used within the kernel as follows: when the
process is interrupted for a clock tick, the value of
offset is subtracted from the current value of the program
counter (pc), and the remainder is multiplied by scale to
derive a result. That result is used as an index into the
histogram array to locate the cell to be incremented. There-
fore, the cell count represents the number of times that the
process was executing code in the subdivision associated
with that cell when the process was interrupted.
The value of scale can be computed as (RATIO * 0200000L),
where RATIO is the desired ratio of bufsiz to profiled
region size, and has a value between 0 and 1. Qualitatively
speaking, the closer RATIO is to 1, the higher the resolu-
tion of the profile information.
The value of bufsiz can be computed as
(size_of_region_to_be_profiled * RATIO).
Profiling is turned off by giving a scale value of 0 or 1,
and is rendered ineffective by giving a bufsiz value of 0.
Profiling is turned off when one of the exec family of func-
tions (see exec(2)) is executed, but remains on in both
child and parent processes after a fork(2). Profiling is
turned off if a buff update would cause a memory fault.
USAGE
The pcsample(2) function should be used when profiling
dynamically-linked programs and 64-bit programs.
SEE ALSO
exec(2), fork(2), pcsample(2), times(2), monitor(3C),
prof(5)
NOTES
In Solaris releases prior to 2.6, calling profil() in a mul-
tithreaded program would impact only the calling LWP; the
profile state was not inherited at LWP creation time. To
profile a multithreaded program with a global profile
buffer, each thread needed to issue a call to profil() at
threads start-up time, and each thread had to be a bound
thread. This was cumbersome and did not easily support
dynamically turning profiling on and off. In Solaris 2.6,
the profil() system call for multithreaded processes has
global impact - that is, a call to profil() impacts all
LWPs/threads in the process. This may cause applications
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System Calls profil(2)
that depend on the previous per-LWP semantic to break, but
it is expected to improve multithreaded programs that wish
to turn profiling on and off dynamically at runtime.
SunOS 5.8 Last change: 11 Feb 1998 3
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