On Mon, 26 Jan 2004, Steve Watt wrote:
> [EMAIL PROTECTED] wrote:
> >do what ping does (ping -f)
> >when you get an ENOBUFS do a usleep for 1 mSec.
> >and then send it again.
you are correct, but I just meant that it requested to sleep 1mSec, not
that the sleep actually WAS 1mSec.
Making udp sockets block would break so many things since
it was always this way since sockets were invented in BSD2.x
>
> So how, exactly, do you actually sleep for 1mSec? I recently did some
> experiments using nanosleep(), and it seems that the minimum sleep time
> is 2 / HZ. I.e. ask for 100nS, get 20mS (on a 10mS-ticking system).
>
> Mind you, that behavior is precisely aligned with what POSIX says should
> happen, since nanosleep() is not allowed to return success before the
> specified amount of time has expired, and you might be calling it 5nS
> before the clock tick. But it does make doing correct Tx pacing a bit
> more challenging.
>
> Tried the same thing with usleep(10000), same result of ~20mS per
> sleep.
>
> Here's the program I tested that with. Same results on a 4.4-RELEASE
> and a 5.2-RELEASE machine.
>
> Numbers from one run:
> 4.4-REL: 1501 loops, 30.017931 elapsed, time per loop: 19998.622 us
> 5.2-REL: 1501 loops, 30.016053 elapsed, time per loop: 19997.371 us
>
> - - - 8< - - -
>
> #include <stdio.h>
> #include <errno.h>
> #include <sys/time.h>
>
> /* Seconds to count loops */
> #define RUNTIME 30
>
> int
> main(int argc, char **argv)
> {
> struct timespec start, now, end, delay, remain;
> double ts, te;
> long loops = 0;
> int rv;
>
> clock_gettime(CLOCK_REALTIME, &start);
> end.tv_sec = start.tv_sec + RUNTIME;
> end.tv_nsec = start.tv_nsec;
>
> do {
> delay.tv_sec = 0;
> delay.tv_nsec = 10000; /* 10uS */
>
> do {
> rv = nanosleep(&delay, &remain);
> delay = remain;
> } while (rv < 0 && errno == EINTR);
>
> ++loops;
> clock_gettime(CLOCK_REALTIME, &now);
> } while ((now.tv_sec == end.tv_sec) ?
> (now.tv_nsec < end.tv_nsec) :
> (now.tv_sec < end.tv_sec));
>
> te = now.tv_sec + (now.tv_nsec / 1000000000.);
> ts = start.tv_sec + (start.tv_nsec / 1000000000.);
>
> printf("%d loops, %f elapsed, ", loops, te - ts);
> printf("time per loop: %.3f us\n", ((te - ts) / loops) * 1000000.);
>
> return 0;
> }
>
>
> --
> Steve Watt KD6GGD PP-ASEL-IA ICBM: 121W 56' 57.8" / 37N 20' 14.9"
> Internet: steve @ Watt.COM Whois: SW32
> Free time? There's no such thing. It just comes in varying prices...
>
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