misc/187668: Profiling timer does not work when setting low interval

[Vasily Postnicov]

>Number:         187668
>Category:       misc
>Synopsis:       Profiling timer does not work when setting low interval
>Confidential:   no
>Severity:       non-critical
>Priority:       low
>Responsible:    freebsd-bugs
>State:          open
>Quarter:        
>Keywords:       
>Date-Required:
>Class:          sw-bug
>Submitter-Id:   current-users
>Arrival-Date:   Mon Mar 17 18:00:00 UTC 2014
>Closed-Date:
>Last-Modified:
>Originator:     Vasily Postnicov
>Release:        Freebsd 10.0
>Organization:
>Environment:
FreeBSD vonbraun 10.0-RELEASE FreeBSD 10.0-RELEASE #1 513d8e6(clocktst): Sun Mar 16 23:02:04 MSK 2014     vasily at vonbraun:/usr/obj/usr/src/sys/MYKERNEL10  am
d64                                                                                                                                                         
>Description:
After this commit:

https://github.com/freebsd/freebsd/commit/5dfd8a110a3e6121977586541b839200faef91da

a statistical profiler in SBCL (Steel Bank Common Lisp) does not work when sampling interval is set very low.

I attach a test which gives unexpected results which confuse SBCL when profiling interval is set to 0.1 ms (just as in sb-sprof test from SBCL):

Start
1
0 100 -15 676200

And with that commit reverted it gives following:
                                                    
Start
14344
0 1000 0 1000

It means that lowest possible profiling interval is set (1 ms). All as expected.
>How-To-Repeat:
Just compile and run my test and wait 15 sec.
>Fix:


Patch attached with submission follows:

#include <sys/time.h>
#include <signal.h>
#include <stdio.h>

int counter = 0;

void handler (int sig)
{
    counter++;
}

int main ()
{
    printf ("Start\n");
    struct sigaction sa;
    sa.sa_handler = handler;
    sa.sa_flags = 0;
    sigemptyset (&sa.sa_mask);
    sigaction (SIGPROF, &sa, NULL);

    struct itimerval val;
    struct itimerval val_old;
    val.it_interval.tv_sec  = 0;
    val.it_interval.tv_usec = 100;

    val.it_value.tv_sec  = 0;
    val.it_value.tv_usec = 100;

    struct timeval time;
    gettimeofday(&time, 0);
    time_t start = time.tv_sec;
    time_t cur = start;
    
    setitimer (2, &val, NULL);

    do
    {
        gettimeofday(&time, 0);
        cur = time.tv_sec;
    }
    while (cur < start+15);

    val.it_value.tv_sec  = 0;
    val.it_value.tv_usec = 0;
    setitimer (2, &val, &val_old);

    printf ("%i\n", counter);
    printf ("%li %li %li %li\n",
            val_old.it_interval.tv_sec,
            val_old.it_interval.tv_usec,
            val_old.it_value.tv_sec,
            val_old.it_value.tv_usec);

    return 0;
}


>Release-Note:
>Audit-Trail:
>Unformatted: