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

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Message-ID: <20190416092911.76nyeodbxu5bsqx4@gondor.apana.org.au>
Date:   Tue, 16 Apr 2019 17:29:11 +0800
From:   Herbert Xu <herbert@...dor.apana.org.au>
To:     Arend Van Spriel <arend.vanspriel@...adcom.com>
Cc:     Johannes Berg <johannes@...solutions.net>,
        Toke Høiland-Jørgensen <toke@...hat.com>,
        Felix Fietkau <nbd@....name>, linux-wireless@...r.kernel.org,
        netdev@...r.kernel.org
Subject: Re: [PATCH 5/5] mac80211: set NETIF_F_LLTX when using intermediate
 tx queues

On Tue, Apr 16, 2019 at 11:17:53AM +0200, Arend Van Spriel wrote:
> On 4/16/2019 10:37 AM, Johannes Berg 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.
> 
> Ok, so the crux is the "never push back to the stack" part? Well, the
> internal TXQ and how that is used is obviously enabling that ;-)

So assuming that these drivers all have a TX queue length of zero
and therefore do not make use of Linux queueing disciplines then
yes techincally LLTX is fine.

However, I must say that it is much better to provide real
congestion feedback to the stack when you can because otherwise
things like UDP may fall apart.

Cheers,
-- 
Email: Herbert Xu <herbert@...dor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt