Date: Sat, 19 Aug 2017 00:29:10 +0200
From: David Lamparter <equinox@diac24.net>
To: linux-wireless@vger.kernel.org
Subject: [POC/GIT] mac80211 multicast rate selection (help wanted!)
Message-ID: <20170818222910.GT773745@eidolon> (sfid-20170819_003422_359325_73798F95)
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Sender: linux-wireless-owner@vger.kernel.org

Hello Linux Wireless hackers,


I've taken up an hacking endeavour in trying to improve multicast on
wifi, specifically to get it off the stupid 1 MBit rate.  Before anyone
yells "that's not allowed by the spec" - it actually is, please refer to
section 9.7.5 of 802.11-2012. ("... using one of the rates included in
the BSSBasicRateSet parameter ...")  Also, Cisco and Aruba are doing
this in their enterprise APs, and it's rather nice.

So, from some completely unrelated datacenter work, I have hacked up the
bridge to hand back down to the driver detailed info on multicast
receivers.  Then I took this and fudged around in the minstrel_ht code
and, well, it gave me 9 MBit/s ;)

Now, I have pretty little no clue about the Linux wireless stack, so I'd
appreciate if someone could tell me how massively wrong I'm doing this
and which places in particular are the wrongest!

You can find the code here:
https://github.com/eqvinox/vpls-linux-kernel/commits/mdb-hack
https://github.com/eqvinox/vpls-iproute2/tree/mdb-hack

Please note that all of this is proof-of-concept level, it probably
leaks tons of memory, has great race conditions and eats your cat for
breakfast.  It also contains some debug printks like this:
[ 9006.253504] mac80211_hwsim hwsim0 wlan0: multi-dst TX: 02:00:00:00:02:00 02:00:00:00:01:00
[ 9006.255007] mac80211_hwsim hwsim0 wlan0: rc 02:00:00:00:02:00 => rate #1
[ 9006.256095] mac80211_hwsim hwsim0 wlan0: rc 02:00:00:00:01:00 => rate #12
[ 9006.257186] mac80211_hwsim hwsim0 wlan0: result rate #1


Cheers,

-David


P.S.: yes, I know about unicast conversion.  But that's not helpful
when, for example, you want to get a 10 MBit multicast TV livestream to
5 simultaneous wifi clients...