On Saturday, 7 November 2015 2:05 AM, Hans Petter Selasky wrote: > On 11/06/15 11:08, Luigi Rizzo wrote: > > On Fri, Nov 6, 2015 at 10:52 AM, Hans Petter Selasky <h...@selasky.org> > wrote: > >> On 11/06/15 09:50, Luigi Rizzo wrote: > >>> > >>> On Fri, Nov 6, 2015 at 9:44 AM, Hans Petter Selasky > >>> <h...@selasky.org> > >>> wrote: > > ... > >>>> Hi, > >>>> > >>>> The C_DIRECT_EXEC flag reduces task switching overhead, that you > >>>> don't have to wakeup a thread to wakeup the dummynet worker > thread. > >>>> It affects timing. > >>> > >>> > >>> Hans, > >>> thanks for the explanation. > >>> > >>> Can you clarify the behaviour of C_DIRECT_EXEC ? > >>> Does this mean that the task is run within some common thread > >>> instead of a dedicated one ? > >> > >> > >> Hi Luigi, > >> > >> C_DIRECT_EXEC means that the timer callback is executed directly from > >> the fast interrupt filter of the timer or IPI. > >> > >>> > >>> If so, for this type of task (dummynet may run at high rate and use > >>> a significant amount of cpu time) it may be a good idea to remove > >>> C_DIRECT_EXEC altogether. > >> > >> > >> The ipfw dummynet code is not run from the timer callback. It is run > >> from a taskqueue. I suspect there is likely a bug somewhere. At the > >> moment it is not clear to me if there is a bug in the callout > >> subsystem, that the when the timer is started with 1 tick delay it > >> doesn't kick in until after 50ms or so at HZ=4000. Or if the dummynet's > task is doing a lot of work for 50ms. > >> I think we need some more information to nail this one. > > > > It certainly does not run for 50ms, but it might occasionally keep the > > thread busy for some 10-50us (I doubt it is longer than that) and > > possibly cause the reschedule request to fall into the interval where > > it should actually run. > > > > So if your theory is correct, it may well be that the callout system > > sees the request "in the past" (possibly as a result as some incorrect > > wraparound, or undefined behaviour on integer wraps) and then the > > event is only recovered when the callout wheel (or whatever is the > > underlying implementation) happens to go again through the entry. > > > > What is so magic in the values we see (400 or 600 or 40ms) i have no idea. > > > > Rasool: > > It might be worth trying to set: > > kern.eventtimer.periodic=1 > > In /boot/loader.conf . Can you test that too? > > You need to reboot before the setting takes into effect.
Hans, Yes, this solves the problem! I will do more checking when I am near my testbed. Thanks for your effort and time! Cheers, Rasool > > Luigi: > > I'm wondering if there is a problem with: > > cpu_new_callout(a,b,c); > > --HPS > > _______________________________________________ > freebsd-net@freebsd.org mailing list > https://lists.freebsd.org/mailman/listinfo/freebsd-net > To unsubscribe, send any mail to "freebsd-net-unsubscr...@freebsd.org" _______________________________________________ freebsd-net@freebsd.org mailing list https://lists.freebsd.org/mailman/listinfo/freebsd-net To unsubscribe, send any mail to "freebsd-net-unsubscr...@freebsd.org"
