a Q on measuring system performance.

[Yan Yu]

Hello, all,

I add some codes in various places relating to file operations inside the
kernel, e.g., fdalloc(), fdused(), fdunused(), fdfree() etc.
I am trying to measure the overhead added by these instrumentation code.
my plan is:
  in my user space program, i have something like the following:
--------------------------------------------
        gettimeofday(&prev_time, NULL);
        for (i=0; i< 1000; i++)
        {
                fd = fopen("tmp", "r" );
                if (fd == NULL)
                {
                        break;
                }
                cnt ++;
        }

        gettimeofday(&cur_time, NULL);
        t_lapse= misc_tv_offset( &cur_time, &prev_time );

----------------------------------------------------
I would run this for the unmodified kernel, and instrumented kernel.
compare the t_lapse, my concern is that t_lapse includes context switch
time when the user process is taken out of run queue.

I also run "gprof" on the program, some related data is:
  %   cumulative   self              self     total
 time   seconds   seconds    calls  ms/call  ms/call  name
 80.0       0.01     0.01     1000     0.01     0.01  __sys_open [3]
 20.0       0.01     0.00     1000     0.00     0.00  __sfp [4]
  0.0       0.01     0.00     1987     0.00     0.00  memcpy [6]
  0.0       0.01     0.00     1000     0.00     0.00  __sflags [283]
  0.0       0.01     0.00     1000     0.00     0.01  fopen [1]

i am wonderinf should I better trust gprof instead?  so 0.01 ms/call for
related file operation is the result.
or is there some other better way to achieve this?

Many thanks in advance!
yan