Re: [RFC net-next v4 0/9] Add support for per-NAPI config via netlink

Joe Damato
2024-10-04T02:33:44Z

On Thu, Oct 03, 2024 at 04:53:13PM -0700, Joe Damato wrote:
> On Thu, Oct 03, 2024 at 04:29:37PM -0700, Stanislav Fomichev wrote:
> > On 10/01, Joe Damato wrote:
>
> [...]
>
> > > 2. This revision seems to work (see below for a full walk through). Is
> > > this the behavior we want? Am I missing some use case or some
> > > behavioral thing other folks need?
> >
> > The walk through looks good!
>
> Thanks for taking a look.
>
> > > 3. Re a previous point made by Stanislav regarding "taking over a NAPI
> > > ID" when the channel count changes: mlx5 seems to call napi_disable
> > > followed by netif_napi_del for the old queues and then calls
> > > napi_enable for the new ones. In this RFC, the NAPI ID generation
> > > is deferred to napi_enable. This means we won't end up with two of
> > > the same NAPI IDs added to the hash at the same time (I am pretty
> > > sure).
> >
> >
> > [..]
> >
> > > Can we assume all drivers will napi_disable the old queues before
> > > napi_enable the new ones? If yes, we might not need to worry about
> > > a NAPI ID takeover function.
> >
> > With the explicit driver opt-in via netif_napi_add_config, this
> > shouldn't matter? When somebody gets to converting the drivers that
> > don't follow this common pattern they'll have to solve the takeover
> > part :-)
>
> That is true; that's a good point.

Actually, sorry, that isn't strictly true. NAPI ID generation is
moved for everything to napi_enable; they just are (or are not)
persisted depending on whether the driver opted in to add_config or
not.

So, the change does affect all drivers. NAPI IDs won't be generated
and added to the hash until napi_enable and they will be removed
from the hash in napi_disable... even if you didn't opt-in to having
storage.

Opt-ing in to storage via netif_napi_add_config just means that your
NAPI IDs (and other settings) will be persistent.

Sorry about my confusion when replying earlier.