Re: [Qemu-devel] [virtio-dev] Re: [virtio-dev] Re: [virtio-dev] Re: [PATCH v1] virtio-net: enable configurable tx queue size

[Wei Wang <wei.w.wang@intel.com>]

On 06/16/2017 04:57 PM, Jason Wang wrote:
>
>
> On 2017年06月16日 11:22, Michael S. Tsirkin wrote:
>>> I think the issues can be solved by VIRTIO_F_MAX_CHAIN_SIZE.
>>>
>>> For now, how about splitting it into two series of patches:
>>> 1) enable 1024 tx queue size for vhost-user, to let the users of 
>>> vhost-user
>>> to easily use 1024 queue size.
>> Fine with me. 1) will get property from user but override it on
>> !vhost-user. Do we need a protocol flag? It seems prudent but we get
>> back to cross-version migration issues that are still pending solution.
What do you have in mind about the protocol flag?

Btw, I just tested the patch of 1), and it works fine with migration 
from the
patched to non-patched version of QEMU. I'll send it out. Please have a 
check.


>> Marc Andre, what's the status of that work?
>>
>>> 2) enable VIRTIO_F_MAX_CHAIN_SIZE,  to enhance robustness.
>> Rather, to support it for more backends.
>
> Ok, if we want to support different values of max chain size in the 
> future. It would be problematic for migration of cross backends, 
> consider the case when migrating from 2048 (vhost-user) to 1024 
> (qemu/vhost-kernel).
>

I think that wouldn't be a problem. If there is a possibility to change the
backend resulting in a change of config.max_change_size, a configuration
change notification can be injected to the guest, then guest will read and
get the new value.

Best,
Wei