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

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

On Thu, Feb 09, 2023 at 12:35:42AM +0200, Alvaro Karsz 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?
> 
> 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..

Amount of time spent on bike-shedding here is mind-boggling.  Pls just
send a new version and we'll go from there.  In the end it's a majority
we don't have to have consensus if we can't get it.

-- 
MST


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