[Buildbot] #3183: fix network "spottiness" on new infra

[Buildbot trac]

#3183: fix network "spottiness" on new infra
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Reporter:  dustin    |       Owner:
    Type:  defect    |      Status:  new
Priority:  critical  |   Milestone:  sys - other
 Version:            |  Resolution:
Keywords:            |
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Comment (by dustin):

 That one was much slower, and again the email warning banner.  Interesting
 fact: when I clicked "Submit changes" it was before the last preview had
 rendered.  So when that last preview *did* render, it found the comment in
 the DB already and warned me that "someone else" had already commented.
 So things are sticking *after* the DB insert, which again points to the
 email submission being the issue.

 Note that the interfaces are arranged as follows: {em0, em1} aggregated in
 lagg0, where the default VLAN is the external subnet; vlan1 uses lagg0
 with vlan tag 80 for the internal subnet.  So adjusting TSO for em0/em1
 affects all communication, not just external.

 Let's try it again!!

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Ticket URL: <http://trac.buildbot.net/ticket/3183#comment:12>
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