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

["Størner.Henrik Juul HSO" <henrik@xxxxxxx>]

Hi,

On 20-07-2014 19:43, Steve Dawson wrote:
> On 07/20/2014 12:35 PM, Henrik Størner wrote:
> > 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.
> >
> > After reading a bunch of docs, blogs etc, I tried these things:
> >    - Dom0 memory fixed at 2 GB, ballooning disabled
> >    - CPU 0+1 dedicated to dom0 (pinned), the domU's configured to
> >      NOT use CPU 0+1
> >    - CPU 4.5 dedicated to the mail server domU
> >    - txqueuelen on the VIF changed to 1024
> >
> > Neither of these appear to make any difference whatsoever
> 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.
Following this, I have disabled hyperthreading - no effect at all.

I can also reproduce it by simply transferring a large file with sftp - 
so is isn't just IMAP/Thunderbird that triggers it.
Dom0 is pinned to PCPU 0, the domU's are free to use any of the 
remaining CPU's. I have tried allocating a full CPU to the mail domU I 
am testing with, this did not have any effect either. Auto-ballooning is 
also disabled so dom0 doesn't run out of memory (it has 2 GB).
One observation: It seems to happen only with IPv4. If I connect to the 
server using IPv6, everything runs fine - mail, sftp etc is OK. Are 
there any IP- or TCP-settings that could cause this?

Regards,
Henrik


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