On 7/13/2022 12:48 AM, Parav Pandit wrote:

quoted

From: Zhu, Lingshan <redacted>
Sent: Sunday, July 10, 2022 10:30 PM

quoted

Showing max_vq_pairs of 1 even when _MQ is not negotiated, incorrectly

says that max_vq_pairs is exposed to the guest, but it is not offered.

quoted

So, please fix the iproute2 to not print max_vq_pairs when it is not

returned by the kernel.
iproute2 can report whether there is MQ feature in the device / driver
feature bits.
I think iproute2 only queries the number of max queues here.

max_vq_pairs shows how many queue pairs there, this attribute's existence
does not depend on MQ, if no MQ, there are still one queue pair, so just
show one.

This netlink attribute's existence is depending on the _MQ feature bit existence.

why? If no MQ, then no queues?

We can break that and report the value, but if we break that there are many other config space bits who doesn’t have good default like max_vq_pairs.

max_vq_paris may not have a default value, but we know if there is no 
MQ, a virtio-net still have one queue pair to be functional.

There is ambiguity for user space what to do with it and so in the kernel space..
Instead of dealing with them differently in kernel, at present we attach each netlink attribute to a respective feature bit wherever applicable.
And code in kernel and user space is uniform to handle them.

I get your point, but you see, by "max_vq_pairs", the user space tool is 
asking how many queue pairs there, it is not asking whether the device 
have MQ.
Even no _MQ, we still need to tell the users that there are one queue 
pair, or it is not a functional virtio-net,
we should detect this error earlier in the device initialization.

I think it is still uniform, it there is _MQ, we return 
cfg.max_queue_pair, if no _MQ, return 1, still by netlink.

Thanks