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Re: [Xen-users] Network connections stalling - Debian Linux domU's

  • To: xen-users@xxxxxxxxxxxxx
  • From: Henrik Størner <henrik@xxxxxxx>
  • Date: Sun, 20 Jul 2014 21:38:05 +0200
  • Delivery-date: Sun, 20 Jul 2014 21:00:58 +0000
  • List-id: Xen user discussion <xen-users.lists.xen.org>

Hi Steve,

on 20-07-2014 19:43, Steve Dawson wrote:

> On 07/20/2014 12:35 PM, Henrik Størner wrote:

>> To cut a long story short, the problem appears to be with the domU 
>> hosting the IMAP server (Dovecot). When a user connects to the
>> IMAP service, the network connection quickly stalls. A "netstat" on
>> the domU shows a very large Send-Q (i.e. data sent, but not
>> acknowledged by the remote end of the connection) - usually around
>> 25000, it ought to be quite small. A tcpdump also shows very large
>> intervals between packets, 10-30 seconds is not uncommon.

> It could be hyper threading, either disable it, or manually pin your
> domU's cpus in pairs. I had a similar issue running a bunch of citrix
> xenapp  (2008 windows terminal) servers with hyper threading enabled,
> when the loads got to about 30% the load averages would skyrocket
> suddenly, pinning the cpus fixed the problem.

I didn't see any high load averages, just a stuck connection. Still,
I'll try to have the hyperthreading disabled - the server is in a
hosting center, so BIOS access requires a bit of work :-(


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