Date: Thu, 1 Jun 1995 15:39:51 -0500 From: Jim Lowe <james@miller.cs.uwm.edu> To: freebsd-hackers@FreeBSD.ORG Subject: Interval timer/System clock Message-ID: <199506012039.PAA20210@miller.cs.uwm.edu>
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I have a question about the system interval timer. I am not sure why it
is behaving the way it is.
Shouldn't the interval timer in the system have a resolution of HZ rather
than HZ/2?
I ran the attached test program on various systems and compiled the following
results:
OS type Processor Min possible interval timer (seconds)
------------- --------- ------------------
OSF 3.0 Alpha 0.005
Solaris 2.4 Sun 4 0.01
Ultrix 4.4 Mips 0.004
FreeBSD 2.0.5 Pentium 0.02
NetBSD 1.0a 386 0.01
Note that FreeBSD returns 0.02 rather than 0.01 which I would expect for a
100 Hz clock.
Also, it would be nice to have a faster interval timer (0.005 secs) for
various Multimedia/Real Time applications. I assume I can just add the line
``OPTIONS "HZ=512"'' to my configuration file, but if I do -- will
I break anything obvious?
Thanks for any help or suggestions.
-Jim
-----snip here for itest.c---
#include <stdio.h>
#include <sys/types.h>
#include <sys/time.h>
#define ITIMER_REAL 0
#define ITIMER_VIRTUAL 1
#define ITIMER_PROF 2
#include <signal.h>
static unsigned int num_ints;
#define NUM_MS 1
void
timer_int()
{
num_ints++;
return;
}
int
main()
{
struct timeval tv, tvo;
struct itimerval it;
struct sigaction action;
double u,v;
action.sa_handler = timer_int;
sigaction(SIGALRM, &action, NULL);
num_ints = 0;
u = 0;
it.it_interval.tv_sec = 0;
it.it_interval.tv_usec = NUM_MS;
it.it_value.tv_sec = 0;
it.it_value.tv_usec = NUM_MS;
setitimer(ITIMER_REAL, &it, NULL);
gettimeofday(&tvo, NULL);
while(1) {
pause();
gettimeofday(&tv, NULL);
v = (tv.tv_sec - tvo.tv_sec) + 1e-6 * (tv.tv_sec - tvo.tv_sec);
if(v - u > 1.0) {
printf("%d %8.8f %8.8f %8.8f secs\r", num_ints, v,
(double)num_ints/v,
v/(double)num_ints);
fflush(stdout);
u = v;
}
}
}
--PAA20140.802039138/miller.cs.uwm.edu--
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