extreme network latency
dillon at backplane.com
Mon Oct 17 13:05:28 PDT 2016
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.
On Mon, Oct 17, 2016 at 12:52 PM, Richard Nyberg <rnyberg at murmeldjur.se>
> 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.
> On 16 October 2016 at 19:14, Matthew Dillon <dillon at 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
> > numerous things that can blow up a LAN. The most common being that a
> > port is wired to loop back into the LAN.
> > -Matt
> > On Sun, Oct 16, 2016 at 9:17 AM, Justin Sherrill <
> justin at shiningsilence.com>
> > wrote:
> >> On Sun, Oct 16, 2016 at 11:49 AM, Richard Nyberg <rnyberg at 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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