newbie question (how to measure time)

[dLux]

Hello!

  I need to  measure the time spent in  one process, and I  need to do
it as exact  as possible (about 1us). 2.2.x kernel  series, Pentium II
proc.

  My first and not-yet-working solution:
 
  I declared 3 variables in the arch/i386/kernel/process.c:

static pid_t ProcID;
static unsigned long long int RunStart;
static unsigned long long int Elapsed;

  ProcID is  the process id,  which needs  to be profiled.  Elapsed is
the time  commulated in the  process running, RunStart is  a temporary
variable.

  I put  some additional code to  the beginning of the  __switch_to in
the arch/i386/kernel/process.c:

        if (prev->pid == ProcID) {
          Elapsed += rdtsc_return()-RunStart;
        } else if (next->pid == ProcID) {
          RunStart = rdtsc_return();
        };

  rdtsc_return() is  a function,  which returns  the Pentium  clock in
long long int format.

  These  code checks  if the  process  we want  to measure  is on  the
schedule or not.
 
  After  it I  wanted to  write a  kernel module,  which registered  a
file in  the /proc,  and it  can set the  ProcID via  it, and  get the
"Elapsed" value from it.
  The problem is that I don't know how I use that variables.

  I tried this:

extern pid_t ProcID;
extern long long int Elapsed;

  But when I want to use my module, it prints:

or2:/projects/boomerang/timer# insmod timermod.o
timermod.o: unresolved symbol ProcID
timermod.o: unresolved symbol Elapsed

(The  timermod.c  originally based  on  the  procfs.c file,  which  is
included in some kernel howto.)

The  System.map  file  in   the  /usr/src/linux-2.2.13  contains  that
symbols:

c021c8c0 b ProcID
c021c8cc b Elapsed

I    copied     the    System.map     into    /boot/System.map-2.2.13,
/lib/modules/2.2.13,  but it  doesn't  help. Do  you  know  how I  can
access those variables?

Another question:
-----------------
Do you know  a better and faster  way to access that  variables? May I
make a device  driver for it? Make  a syscall? Please refer  me to the
URL when I can study these materials.

Thanks for any help in advance,

dLux
--
              God save the screen!