netdev - Re: Multicast: handling of STA disconnect

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Date:   Mon, 20 Mar 2023 22:55:17 +0530
From:   Ujjal Roy <royujjal@...il.com>
To:     Nikolay Aleksandrov <razor@...ckwall.org>
Cc:     roopa@...dia.com, nikolay@...dia.com, netdev@...r.kernel.org,
        Kernel <linux-kernel@...r.kernel.org>,
        bridge@...ts.linux-foundation.org
Subject: Re: Multicast: handling of STA disconnect

Hi Nik,

Flushing MDB can only be done when we are managing it per station not
per port. For that we need to have MCAST_TO_UCAST, EHT and FAST_LEAVE.

Here one more point is - some vendors may offload MCAST_TO_UCAST
conversion in their own FW to reduce CPU.

So, the best way is to have MCAST_TO_UCAST enabled and MDB will become
per station, so we can delete MDB on disconnect. Shall, I create one
patch for review?

Thanks,
UjjaL Roy

On Mon, Mar 20, 2023 at 5:38 PM Nikolay Aleksandrov <razor@...ckwall.org> wrote:
>
> On 20/03/2023 13:45, Ujjal Roy wrote:
> > Hi Nikolay,
> >
> > I have some query on multicast. When streams running on an STA and STA
> > disconnected due to some reason. So, until the MDB is timed out the
> > stream will be forwarded to the port and in turn to the driver and
> > dropps there as no such STA.
> >
> > So, is the multicast_eht handling this scenario to take any action
> > immediately? If not, can we do this to take quick action to reduce
> > overhead of memory and driver?
> >
> > I have an idea on this. Can we mark this port group (MDB entry) as
> > INACTIVE from the WiFi disconnect event and skip forwarding the stream
> > to this port in br_multicast_flood by applying the check? I can share
> > the patch on this.
> >
> > Thanks,
> > UjjaL Roy
>
> Hi,
> Fast leave and EHT (as that's v3's fast leave version) are about quickly converging when
> a leave is received (e.g. when there are no listeners to quickly remove the mdb). They
> don't deal with interface states (IIUC). Why don't you just flush the port's mdb entries
> on disconnect? That would stop fwding.
>
> Cheers,
>  Nik
>
>