On Mon, Feb 19, 2018 at 09:58:30AM +0000, Laurence Pawling via freebsd-xen 
wrote:
> Hi all,
> 
>  
> 
> I’m wondering if anyone here has seen this issue before, I’ve spent the last 
> couple of days troubleshooting:
> 
>  
> 
> Platform:
> 
> Host: XenServer 7.0 running on 2 x E2660-v4, 256GB RAM
> 
> Server VM: FreeBSD 11 (tested on 11.0-p15 and 11.1-p6), 2GB RAM (also tested 
> with 32GB RAM), 1x50GB HDD, 1 x NIC, 2 or more vCPUs in any combination (2 
> sockets x 1 core, 1 socket x 2 cores, …)
> 
> Client VM: FreeBSD 11, any configuration of vCPUs, RAM and HDD.
> 
>  
> 
> Behaviour:
> 
> Sporadic interruption of TCP sessions when utilising the above machine as a 
> “server” with “clients” connecting. Looking into the communication with 
> pcap/Wireshark, you see a TCP Dup Ack sent from both ends, followed by the 
> client sending an RST packet, terminating the TCP session. We have also seen 
> evidence of the client sending a Keepalive packet, which is ACK’d by the 
> server before the RST is sent from the client end.
> 
>  
> 
> To recreate:
> 
> On the above VM, perform a vanilla install of nginx:
> 
> pkg install nginx
> 
> service nginx onestart
> 
> Then on a client VM (currently only tested with FreeBSD), run the following 
> (or similar):
> 
> for i in {1..10000}; do if [ $(curl -s -o /dev/null -w "%{http_code}" 
> http://10.2.122.71) != 200 ] ; then echo "error"; fi; done
> 
> When vCPUs=1 on the server, I get no errors, when vCPUs>1 I get errors 
> reported. The frequency of errors *seems* to be proportional to the number of 
> vCPUs, but they are sporadic with no clear periodicity or pattern, so that is 
> just anecdotal. Also, the problem seems by far the most prevalent when 
> communicating between two VMs on the same host, in the same VLAN. Xen still 
> sends packets via the switch rather than bridging internally between the 
> interfaces.

When using >1 vCPUs can you set hw.xn.num_queues=1 on
/boot/loader.conf and try to reproduce the issue?

I'm afraid this is rather related to multiqueue (which is only used
if >1 vCPUs).

Thanks, Roger.
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