'Live' Migrate messes up NTP on FreeBSD domU - any suggestions?

[Roger Pau Monné]

Adding Wei to the Cc list since he added the multiqueue functionality.

On Mon, Jul 25, 2016 at 02:59:02PM +0100, Karl Pielorz wrote:
> 
> --On 22 July 2016 13:55 +0200 Roger Pau Monné <roger.pau at citrix.com> wrote:
> 
> > In my environment I've migrated a FreeBSD VM with 2 cpus for > 100
> > consecutive times without seeing any issues (or freezes), although this
> > was  with OSS Xen and without xe-guest-utilities. Karl, have you tested
> > HEAD  recently?
> 
> Ok, I have tested this with r303286 - it seems to work OK. The hosts gain no
> time that I can see while migrating, and NTP stays happy.
> 
> I did get a panic after about 40 migrations - but that seems to be some
> network issue or something...
> 
>   ('panic called with 0 available queues / dbt_trace_self_wrapper / vpanic /
> kassert_panic / xn_txq_mq_start / ether_output / udp_send / sosend_dgram /
> kern_sendit / sendit / sys_sendto / amd64_syscall / Xfast_syscall)

I haven't been able to reproduce this, but I think it's possible that if you 
migrate an active netfront xn_txq_mq_start might be called during the 
migration, just in the middle of the setup_device reconfiguation (while 
info->num_queues is 0).

Wei, I think netif_disconnect_backend should set IFF_DRV_OACTIVE in order to 
notify the net subsystem that the queues are full, so no further calls to 
xn_txq_mq_start happen until the resume has finished, do you agree?

Roger.