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

[Alvaro Karsz <alvaro.karsz@solid-run.com>]

> > 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?

Sorry, I'm not sure I understand your question.

The feature is implemented in the linux kernel
https://github.com/torvalds/linux/commit/699b045a8e43bd1063db4795be685bfd659649dc
So we'll always have kernel versions accepting this feature, if offered.

> > (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.

Yes, but resetting the queues doesn't require a control command.
If a server has 64K queues, and a user wants to set all coalescing
parameters to X (maybe with ethtool), it will generate 64K control
commands..