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Today's Topics:
1. the myth of spectrum scarcity (Dave Taht)
2. openwifi presentation (Dave Taht)
3. Re: [PATCH mac80211-next v8] mac80211: Switch to a virtual
time-based airtime scheduler (Toke Høiland-Jørgensen)
---------- Forwarded message ----------
From: Dave Taht <dave.taht@gmail.com>
To: Make-Wifi-fast <make-wifi-fast@lists.bufferbloat.net>
Cc:
Bcc:
Date: Mon, 21 Jun 2021 09:55:24 -0700
Subject: [Make-wifi-fast] the myth of spectrum scarcity
this was really good:
https://ecfsapi.fcc.gov/file/7020396128.pdf
--
Latest Podcast:
https://www.linkedin.com/feed/update/urn:li:activity:6791014284936785920/
Dave Täht CTO, TekLibre, LLC
---------- Forwarded message ----------
From: Dave Taht <dave.taht@gmail.com>
To: Make-Wifi-fast <make-wifi-fast@lists.bufferbloat.net>
Cc:
Bcc:
Date: Mon, 21 Jun 2021 10:07:23 -0700
Subject: [Make-wifi-fast] openwifi presentation
https://media.libreplanet.org/u/libreplanet/m/openwifi-project-the-dawn-of-the-free-libre-wifi-chip/
--
Latest Podcast:
https://www.linkedin.com/feed/update/urn:li:activity:6791014284936785920/
Dave Täht CTO, TekLibre, LLC
---------- Forwarded message ----------
From: "Toke Høiland-Jørgensen" <toke@redhat.com>
To: Felix Fietkau <nbd@nbd.name>
Cc: make-wifi-fast@lists.bufferbloat.net, Rajkumar Manoharan <rmanohar@codeaurora.org>, Kan Yan <kyan@google.com>, Yibo Zhao <yiboz@codeaurora.org>, linux-wireless@vger.kernel.org
Bcc:
Date: Tue, 22 Jun 2021 16:25:03 +0200
Subject: Re: [Make-wifi-fast] [PATCH mac80211-next v8] mac80211: Switch to a virtual time-based airtime scheduler
Toke Høiland-Jørgensen <toke@redhat.com> writes:
> This switches the airtime scheduler in mac80211 to use a virtual time-based
> scheduler instead of the round-robin scheduler used before. This has a
> couple of advantages:
>
> - No need to sync up the round-robin scheduler in firmware/hardware with
> the round-robin airtime scheduler.
>
> - If several stations are eligible for transmission we can schedule both of
> them; no need to hard-block the scheduling rotation until the head of the
> queue has used up its quantum.
>
> - The check of whether a station is eligible for transmission becomes
> simpler (in ieee80211_txq_may_transmit()).
>
> The drawback is that scheduling becomes slightly more expensive, as we need
> to maintain an rbtree of TXQs sorted by virtual time. This means that
> ieee80211_register_airtime() becomes O(logN) in the number of currently
> scheduled TXQs because it can change the order of the scheduled stations.
> We mitigate this overhead by only resorting when a station changes position
> in the tree, and hopefully N rarely grows too big (it's only TXQs currently
> backlogged, not all associated stations), so it shouldn't be too big of an
> issue.
>
> To prevent divisions in the fast path, we maintain both station sums and
> pre-computed reciprocals of the sums. This turns the fast-path operation
> into a multiplication, with divisions only happening as the number of
> active stations change (to re-compute the current sum of all active station
> weights). To prevent this re-computation of the reciprocal from happening
> too frequently, we use a time-based notion of station activity, instead of
> updating the weight every time a station gets scheduled or de-scheduled. As
> queues can oscillate between empty and occupied quite frequently, this can
> significantly cut down on the number of re-computations. It also has the
> added benefit of making the station airtime calculation independent on
> whether the queue happened to have drained at the time an airtime value was
> accounted.
>
> Co-developed-by: Yibo Zhao <yiboz@codeaurora.org>
> Signed-off-by: Yibo Zhao <yiboz@codeaurora.org>
> Signed-off-by: Toke Høiland-Jørgensen <toke@redhat.com>
Hey Felix
Had a chance to look at this yet? :)
-Toke
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