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From:   Toke =?utf-8?Q?H=C3=B8iland-J=C3=B8rgensen?= <toke@redhat.com>
To:     Yibo Zhao <yiboz@codeaurora.org>
Cc:     Johannes Berg <johannes@sipsolutions.net>,
        linux-wireless@vger.kernel.org,
        make-wifi-fast@lists.bufferbloat.net,
        John Crispin <john@phrozen.org>,
        Lorenzo Bianconi <lorenzo@kernel.org>,
        Felix Fietkau <nbd@nbd.name>,
        linux-wireless-owner@vger.kernel.org
Subject: Re: [PATCH RFC/RFT 4/4] mac80211: Apply Airtime-based Queue Limit (AQL) on packet dequeue
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Date:   Wed, 25 Sep 2019 10:11:08 +0200
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Yibo Zhao <yiboz@codeaurora.org> writes:

> So if it is going to work together with virtual time based mechanism in=
=20
> the future, the Tx criteria will be met both of below conditions,
>         1. Lower than g_vt
>         2. Lower than IEEE80211_AIRTIME_QUEUE_LIMIT

> Are we going to maintain two kinds of airtime that one is from=20
> estimation and the other is basically from FW reporting?

Yes, that was my plan. For devices that don't have FW reporting of
airtime, we can fall back to the estimation; but if we do have FW
reporting that is most likely going to be more accurate, so better to
use that for fairness...

> Meanwhile, airtime_queued will also limit the situation that we only
> have a station for transmission. Not sure if the peak throughput will
> be impacted. I believe it may work fine with 11ac in chromiumos, how
> about 11n and 11a?

Well, we will need to test that, of course. But ath9k shows that it's
quite possible to run with quite shallow buffers, so with a bit of
tuning I think we should be fine. If anything, slower networks need
*fewer* packets queued in the firmware, and it's *easier* for the host
to keep up with transmission.

> Anyway, I think this approach will help to improve performance of the=20
> virtual time based mechanism since it makes packets buffered in host=20
> instead of FW's deep queue. We have observed 2-clients case with=20
> different ratio in TCP fails to maintain the ratio because the packets=20
> arriving at host get pushed to FW immediately and thus the airtime=20
> weight sum is 0 in most of time meaning no TXQ in the rbtree. For UDP,=20
> if we pump load more than the PHY rate, the ratio can be maintained=20
> beacuse the FW queue is full and packtes begin to be buffered in host=20
> making TXQs staying on the rbtree for most of time. However, TCP has its=
=20
> own flow control that we can not push enough load like UDP.

Yes, fixing that is exactly the point of this series :)

-Toke