profil(2) — AIX PS/2 1.2.1



PROFIL(2,L)                 AIX Technical Reference                 PROFIL(2,L)



-------------------------------------------------------------------------------
profil



PURPOSE

Starts and stops execution profiling.

SYNTAX

#include <mon.h>
#include <sys/param.h>

void profil (shortbuff, bufsiz, offset, scale)
- or -
void profil (profbuff, -1, 0, 0)

short *shortbuff;
struct prof *profbuff;
unsigned int bufsiz, offset, scale;

DESCRIPTION

The profil system call arranges to record a histogram of periodically sampled
values of the calling process's program counter.

If the bufsiz parameter has any value but -1, then the parameters to profil are
interpreted as shown in the first syntax definition.  The shortbuff parameter
points to an area of memory, and its length (in bytes) is given by the bufsiz
parameter.

After this call, the user's program counter (pc) is examined CLK_TCK times a
second.  CLK_TCK is a macro defined in <time.h>.  The value of the offset
parameter is subtracted from the pc, and the result is multiplied by the value
of the scale parameter.  If the resulting number is less than
bufsiz / sizeof(short), then the corresponding short inside shortbuff is
incremented.

The least significant 16 bits of the scale parameter are interpreted as an
unsigned, fixed-point fraction with a binary point at the left.  The most
significant 16 bits of scale are ignored.  For example:

Octal      Hex      Meaning

0177777    0xFFFF   Maps approximately each pair of bytes in the instruction
                    space to a unique short in shortbuff.
077777     0x7FFF   Maps approximately every four bytes to a short in
                    shortbuff.
01         0x0001   Maps all instructions to the first short in shortbuff,
                    producing a noninterrupting core clock.
0          0x0000   Turns profiling off.



Processed November 7, 1990        PROFIL(2,L)                                 1



PROFIL(2,L)                 AIX Technical Reference                 PROFIL(2,L)




Mapping each byte of the instruction space to an individual short in shortbuff
is not possible.

If the second parameter (bufsize) has the value -1, then the parameters to
profil are interpreted as shown in the second syntax definition.  In this case,
the offset and scale parameters are ignored, and profbuff points to an array of
prof structures.  The prof structure is defined in the mon.h header file, and
it contains the following members:

      daddr_t p_low;
      daddr_t p_high;
      unsigned short *p_buff;
      int  p_bufsize;
      int  p_scale;

If the p_scale member has the value -1, then a value for it is computed based
on p_low, p_high, and p_bufsize; otherwise p_scale is interpreted like the
scale argument in the first synopsis.  The p_high members in successive
structures must be in ascending sequence.  The array of structures is
terminated with a structure containing a p_high member set to 0.

Profiling is turned off:

  o If the value of the scale parameter is 0.
  o When an exec system call is executed
  o If updating the buffer pointed to by the shortbuff or profbuff parameter
    would cause a memory fault.

Profiling is rendered ineffective by giving a value of "0" for the bufsiz
parameter.

Profiling remains on in both the child process and the parent process after a
fork system call.

Note:  The profiling rate is machine dependent.  A program should use the
       defined constant IHZ instead of assuming a specific value.

RELATED INFORMATION

In this book:  "exec:  execl, execv, execle, execve, execlp, execvp," "fork,
vfork," and "monitor, monstartup, moncontrol."

The cc and prof commands in AIX Operating System Commands Reference.











Processed November 7, 1990        PROFIL(2,L)                                 2

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