That kinda sounds like an interrupt issue, in which case I suggest turning
polling on for both interfaces.  ifconfig <blah> polling ought to do it.
If that fixes the problem, then it is definitely interrupt-related.

-Matt

On Mon, Oct 17, 2016 at 12:52 PM, Richard Nyberg <rnyb...@murmeldjur.se>
wrote:

> Thanks again for your suggestions.
>
> Actually it's much stranger than I thought. While troubleshooting I
> had this configuration:
>
> df (em0) -> switch <- desktop
>
> No other devices or network interfaces were connected. In this
> configuration there was no problem at all with latency. I then plugged
> in the cable with internet acces like below:
>
> internet <- (re0) df (em0) -> switch <- desktop
>
> In this configuration the latency problems immediately showed. The fun
> thing is that when I unplugged the re0 interface again the em0
> interface stopped responding at all, until I put the cable back to
> re0. Then em0 was back but with latency problems.
>
> Another data point is that while I downloaded a large file at speed
> from the internet via df to my desktop in the above configuration and
> pinged from the desktop to df at the same time, the latency problems
> were gone. Until the download was finished and they started again.
>
> -Richard
>
> On 16 October 2016 at 19:14, Matthew Dillon <dil...@backplane.com> wrote:
> > Look for a packet loop on the interface.  Use tcpdump on the interface to
> > see if there are excess packets being generated from somewhere.  There
> are
> > numerous things that can blow up a LAN.  The most common being that a
> switch
> > port is wired to loop back into the LAN.
> >
> > -Matt
> >
> > On Sun, Oct 16, 2016 at 9:17 AM, Justin Sherrill <
> jus...@shiningsilence.com>
> > wrote:
> >>
> >> On Sun, Oct 16, 2016 at 11:49 AM, Richard Nyberg <rnyb...@murmeldjur.se
> >
> >> wrote:
> >> > Thanks!
> >> >
> >> > Here are some more datapoints.
> >>
> >> I think the only constant at this point is the internal interface on
> >> the DragonFly system.  If you hook the em0 interface that's currently
> >> internal on the DragonFly machine up to your Internet link (i.e.
> >> reverse which interface is internal or external), does it still
> >> perform badly?
> >>
> >> If it doesn't work well, then that interface is bad.  I'd be
> >> surprised, cause I've seen network ports go bad very rarely, but it's
> >> possible.  Plus, I don't have any other ideas.
> >
> >
>

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