netdev - Re: [PATCH 5/5] mac80211: set NETIF_F_LLTX when using intermediate tx queues

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Date:   Tue, 16 Apr 2019 11:39:56 +0200
From:   Johannes Berg <johannes@...solutions.net>
To:     Herbert Xu <herbert@...dor.apana.org.au>
Cc:     Toke Høiland-Jørgensen <toke@...hat.com>,
        Arend Van Spriel <arend.vanspriel@...adcom.com>,
        Felix Fietkau <nbd@....name>, linux-wireless@...r.kernel.org,
        Eric Dumazet <eric.dumazet@...il.com>, netdev@...r.kernel.org
Subject: Re: [PATCH 5/5] mac80211: set NETIF_F_LLTX when using intermediate
 tx queues

On Tue, 2019-04-16 at 17:37 +0800, Herbert Xu wrote:
> On Tue, Apr 16, 2019 at 11:33:50AM +0200, Johannes Berg wrote:
> > On Tue, 2019-04-16 at 10:33 +0100, Toke Høiland-Jørgensen wrote:
> > > 
> > > > It is true because we have an entire buffering layer in mac80211 (in
> > > > this case at least) and never push back to the stack.
> > > 
> > > I'm wondering if we should be?
> > 
> > I don't think so? We'd just buffer packets in yet another place.
> 
> But you do realise that you're giving up on the rich queueing
> functionality that Linux provides (net/sched),

Yes, that was a trade-off we always knew about. The model that Linux
provides is just not suited for wifi.

> not to mention
> breaking certain applications that rely on congestion feedback?

This I don't understand. The congestion feedback happens through socket
buffer space etc. which is still there (as long as nobody sneaks in an
skb_orphan() call)

johannes