Networking under Xen

[Sydney Meyer]

Also i have noticed, when TSO is disabled IPv4 TCP Performance also drops from ~10 Gb/s to ~3 Gb/s, the same as with IPv6. I have read threads from around 2010 about the networking stack not having support for TSO on IPv6 Packets. May this be the problem in this case?

> On 14 Jul 2015, at 23:44, Sydney Meyer <syd.meyer at gmail.com> wrote:
> 
> 
>> On 14 Jul 2015, at 18:15, Mark Felder <feld at FreeBSD.org> wrote:
>> 
>> 
>> 
>> On Tue, Jul 14, 2015, at 07:36, Sydney Meyer wrote:
>>> Hello everybody,
>>> 
>>> i have noticed some odd behaviour with networking under Xen with FreeBSD
>>> 10 as a DomU.
>>> 
>>> - IPv6 (TCP) bandwith drops from ~10 Gbit/s IPv4 to around 3 Gbit/s IPv6.
>>> (measured with iperf)
>>> 
>> 
>> What is the "before" and "after" here? When is FreeBSD successfully
>> doing 10Gbit/s and when isn't it? Is pf enabled? Are you scrubbing?
> 
> With two clean 10.1 AMD64 DomU installations both with a single, pinned cpu, without pf enabled the TCP performance between the two hosts, measured with iperf, differs between ~10 Gb/s on IPv4 and ~3 Gb/s on IPv6. With pf enabled and "scrub in all" the difference is almost the same.
>> 
>>> - Dropped/Stalled Connections with TCP Segmentation Offload and pf
>>> enabled.
>>> 
>> 
>> TSO is a known issue. I've been turning it off for years to get FreeBSD
>> to play nice on Xen.
> 
> This one i am still investigating, because it happens only in "certain" situations (which are not clear to me, atm), but the host seems to drop ACK Packets in some situations like when connected to via IPSEC or via double NAT. This happens only when pf it actually enabled. Disabling TSO on the xn-interface seems to help.
>> 
>>> - IPSEC-enabled Kernel TCP Performance drops from ~10 Gbit/s to ~200
>>> Mbit/s (iperf).
>>> 
>> 
>> Are you saying FreeBSD non-IPSEC kernel can do 10Gbit/s TCP performance,
>> but IPSEC kernel immediately drops it to 200Mbit/s?
> 
> As for the apparent performance drop with IPSEC enabled Kernels without security associations installed, i am unable to reproduce this now, not on 10.0 or 10.1 nor 10 STABLE. Only when actually _using_ IPSec the performance drops from ~10Gb/s to around ~200Mb/s whether actually encrypting esp traffic or not.
> This clearly must have been a mistake on my side, although i could have sworn that i checked this two times before asking on the forums and the -net mailing list a few weeks ago. Well then, i am sincerely sorry about this one.
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>