Re: vhost-user technical isssues

[Tetsuya Mukawa <mukawa-AlSX/UN32fvPDbFq/vQRIQ@public.gmane.org>]

Hi Xie,

(2014/11/14 9:22), Xie, Huawei wrote:
>> I think so. I guess we need to consider 2 types of restarting. One is
>> virtio-net driver restarting, the other is vhost-user backend
>> restarting. But, so far, it's nice to start to think about virtio-net
>> driver restarting first. Probably we need to implement a way to let
>> vhost-user backend know virtio-net driver is restarted. I am not sure
>> what is good way to let vhost-user backend know it. But how about
>> followings RFC? 
> I checked your code today, and didn't find the logic to deal with virtio reconfiguration.
Yes.
I guess the first implementation of librte_vhost may just replace
vhost-example function.
Probably vhost-example doesn't think about restarting.
Because of this, I haven't implemented.

> My thought without new message support: When vhost-user receives
> another configuration message since last time it is ready for
> processing, then we could release it from data core, and process the
> next reconfiguration message, and then re-add it to data core when it
> is ready again(check new kick message as before). The candidate
> message is set_mem_table. It is ok we keep the device on data core
> until we receive the new reconfiguration message. Just waste vhost
> some cycles checking the avail idx.

For example, let's assume DPDK app1 is started on guest with virtio-net
device port.
If DPDK app1 on guest is stopped, and other DPDK app2 on guest is
started without virtio-net device port.
Hugepages DPDK app1 used will be used by DPDK app2.
It means the memory accessed by vhost-user backend might be changed by
DPDK app2.
And vhost-user backend will be crashed.
So I guess we need some kinds of reset message.

Thanks,
Tetsuya