Date: Sat, 04 Oct 2014 10:02:23 -0600 From: Ian Lepore <ian@FreeBSD.org> To: Paul Albrecht <palbrecht@glccom.com> Cc: "freebsd-hackers@freebsd.org" <freebsd-hackers@freebsd.org>, Adrian Chadd <adrian@freebsd.org> Subject: Re: freebsd 10 kqueue timer regression Message-ID: <1412438543.12052.107.camel@revolution.hippie.lan> In-Reply-To: <8587D819-AA2F-4387-A4E9-523014384672@glccom.com> References: <8ABC0977-FB8F-45E7-ACCC-BFA92EE22E1C@glccom.com> <CAJ-VmonJQKWeW7K6%2BjY6=FpmZrm%2B6HQOuBmhhjJEapyVpwNFdQ@mail.gmail.com> <8587D819-AA2F-4387-A4E9-523014384672@glccom.com>
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On Thu, 2014-10-02 at 13:13 -0500, Paul Albrecht wrote:
> On Oct 2, 2014, at 12:18 PM, Adrian Chadd <adrian@freebsd.org> wrote:
>
> > On 2 October 2014 08:07, Paul Albrecht <palbrecht@glccom.com> wrote:
> >>
> >> Hi,
> >>
> >> Whatÿs up with freebsd 10? Iÿm testing some code that uses the kqueue timer for timing and it doesnÿt work because the precision of the timer is off.
> >
> > Can you provide a test case for it?
>
> Hereÿs the code:
>
> #include <stdio.h>
> #include <stdlib.h>
> #include <string.h>
> #include <unistd.h>
> #include <errno.h>
> #include <sys/types.h>
> #include <sys/event.h>
> #include <sys/time.h>
>
> int
> main(void)
> {
> int i,msec;
> int kq,nev;
> struct kevent inqueue;
> struct kevent outqueue;
> struct timeval start,end;
>
> if ((kq = kqueue()) == -1) {
> fprintf(stderr, "kqueue error!? errno = %s", strerror(errno));
> exit(EXIT_FAILURE);
> }
> EV_SET(&inqueue, 1, EVFILT_TIMER, EV_ADD | EV_ENABLE, 0, 20, 0);
>
> gettimeofday(&start, 0);
> for (i = 0; i < 50; i++) {
> if ((nev = kevent(kq, &inqueue, 1, &outqueue, 1, NULL)) == -1) {
> fprintf(stderr, "kevent error!? errno = %s", strerror(errno));
> exit(EXIT_FAILURE);
> } else if (outqueue.flags & EV_ERROR) {
> fprintf(stderr, "EV_ERROR: %s\n", strerror(outqueue.data));
> exit(EXIT_FAILURE);
> }
> }
> gettimeofday(&end, 0);
>
> msec = ((end.tv_sec - start.tv_sec) * 1000) + (((1000000 + end.tv_usec - start.tv_usec) / 1000) - 1000);
>
> printf("msec = %d\n", msec);
>
> close(kq);
> return EXIT_SUCCESS;
> }
>
> When I run it on my system I get these results:
>
> ./a.out
> msec = 1072
> ./a.out
> msec = 1071
> ./a.out
> msec = 1071
>
> Which is over about 3.5 times the wait time per second.
>
>
> >
> > I just chased down one of those recently; maybe it's the same thing
> > (callout() API changes.)
> >
> >
FYI, I just committed the fix to -current as r272528. I'll MFC it to
10-stable in 3 days, and then we'll see if it can get into the 10.1
release cycle.
-- Ian
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