Re: [virtio-comment] [PATCH] virtio-net: support per-queue coalescing moderation

["Michael S. Tsirkin" <mst@redhat.com>]

On Wed, Feb 08, 2023 at 10:08:41PM +0000, Parav Pandit wrote:
> 
> > From: Alvaro Karsz <alvaro.karsz@solid-run.com>
> > Sent: Wednesday, February 8, 2023 4:56 PM
> 
> > > Alvaro,
> > > Do you know if any software used it? Can you get some real data?
> > 
> > I implemented this feature in our DPU, so at least 1 vendor is using this feature
> 
> But which software (virtio net driver) in which OS is using this?
> 
> > (I will add support for the per vq command of course).
> > I really don't know about other vendors..
> >
> > You are suggesting to reserve the command and feature bit for safety, so, if we
> > reserve them, why not just use them? What do we lose here?
> > 
> If it is used by some unknown software, only that sw breaks by using non release spec.
> If we use it by changing the definition, it may break that unknown sw.
> If we know there is no known sw, we are better of with redefinition (by adding vqn, and by removing tx,rx from it).
> 
> > Not having this feature/command even complicates things now that we are
> > talking about removing the RX and TX from the per vq command, how do you
> > change parameters to all TX queues? to all RX queues? we'll need 2 special
> > indexes, so we now need le32 to hold the queue index.
> No need for special index.
> How does a driver disable all queues or reset all queues? -> One by one.
> So if user want to change for all TXQ, sw can do it one by one by iterating TXQ vqns.

I think we can split this effort in two parts:

1. add a new command and feature bit
2. drop the old command


Looks like there's consensus on 1?  And it looks like Alvaro wants to
work on 1 but not 2. Once that is in Parav can work on 2 if he wants to.

-- 
MST