Re: em device hangs on ifconfig alias ...


On Fri, 7 Jul 2006, User Freebsd wrote:

I think that I have patched, built and loaded the em(4) kernel module correctly. After applying the patch there were no rejects, before building the module I intentionally appended " (patched)" to its version string in if_em.c, and could see that in dmesg every time I loaded the module: em1: <Intel(R) PRO/1000 Network Connection Version - 3.2.18 (patched)>

Is it possible that we're going at this issue backwards? It isn't the lack of ARP packet going out that is causing the problems with moving IPs, but that delay that we're seeing when aliasing a new IP on the stack? The ARP packet *is* being attempted, but is timing out before the re-init is completing?

Yes -- basically, there are two problems:

(1) A little problem, in which an arp announcement is sent before the link has
settled after reset.

(2) A big problem, in which the interface is gratuitously recent requiring
long settling times.

I'd really like to see a fix to the second of these problems (not resetting when an IP is added or removed, resulting in link renegotiation); the first one I'm less concerned about, although it would make some amount of sense to do an arp announcement when the link goes up.

Robert N M Watson
Computer Laboratory
University of Cambridge
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Relevant Pages

  • Re: em device hangs on ifconfig alias ...
    ... After applying the patch there were no rejects, before building the module I intentionally appended " " to its version string in if_em.c, and could see that in dmesg every time I loaded the module: em1: ... It isn't the lack of ARP packet going out that is causing the problems with moving IPs, but that delay that we're seeing when aliasing a new IP on the stack? ... long settling times. ... I thought I remember a developer working on the em driver saying just before 6.1 was released that this reset was needed and couldn't be avoided to ensure performance of the device to work at its best, I can't remember his explanation, but this topic has come up before, of course anything is possible to fix. ...
    (freebsd-stable)
  • Re: em device hangs on ifconfig alias ...
    ... Is it possible you're seeing an interaction between the reset generated as part of IP address changing, and the time it takes to negotiate link? ... It's possible that the arp packets are being eaten during the link negotiation, so for systems negotiating quickly then the arp packet is seen on other hosts, and otherwise not... ... I was able to see it by running two tcpdump instances - one on the EM machine running in background and another running elsewhere on the same subnet. ... After applying the patch there were no rejects, before building the module I intentionally appended " " to its version string in if_em.c, and could see that in dmesg every time I loaded the module: ...
    (freebsd-stable)