Re: [PATCH v5] virtio-net: clarify coalescing parameters settings

[Heng Qi <hengqi@linux.alibaba.com>]

On Thu, 13 Jun 2024 02:13:50 -0400, "Michael S. Tsirkin" <mst@redhat.com> wrote:
> On Tue, Jun 11, 2024 at 05:43:18PM +0000, Parav Pandit wrote:
> > 
> > 
> > > From: Michael S. Tsirkin <mst@redhat.com>
> > > Sent: Tuesday, June 11, 2024 10:00 PM
> > 
> > 
> > > How we can we make progress with
> > > the realease but sure we don't make backwards compat a pain?
> > > 
> > > Ideas?
> > >
> > There is no functional break with this relaxation.
> > Device set some non-zero defaults and driver didn't modify them.... 
> > Anything broken? Unlikely.
> > And device/driver has better performance, is that a problem? Unlikely.
> > 

Sorry, my vacation just ended.

> 
> Yes, it is possible. Driver can cache values it sets
> and never query device with get.

Don't we already have a lot of behaviors to drive queries from devices?
RSS context, device stats.

> Before anything is set, driver will report incorrect values.

Devices that are widely supported and supported by good practices should have
any initialization value. Just reporting 0 is incorrect value. Although the
spec now says so.

> What will break as a result? Hard to predict.
> 
> 
> Given the patch is big, I am inclined to say it just should use
> a feature bit.
> 

This doesn't seem to break anything in my opinion, we just told the device that
now you can set more values.

Using new feature bits does not seem necessary.

Thanks.

> -- 
> MST
>