[Cerowrt-devel] Managed to break 802.11n (on a 3800)
Dave Taht
dave.taht at gmail.com
Thu Jan 16 14:08:02 PST 2014
Several quick notes:
(I am behind on my mail)
On Thu, Jan 16, 2014 at 10:03 AM, Aaron Wood <woody77 at gmail.com> wrote:
> All,
>
> I'm noting this here in case anyone is interested. After I write this up,
> I'm going to start from scratch on the configuration, and factory-reset the
> router.
>
> =====
>
> The 5GHz radio on my 3800 seems to be in a very odd state. I'm not quire
> sure what state it's in, but it seems to be only doing HT20 1x1. And in a
> fairly broken manner at that.
Well, I've noted that until we get per station queueing in the ath9k driver
itself, wifi performance is not going to be very good.
> Running the rrul test (over wifi directly to the router as the netserver),
> tcp uploads were 25Mbps or so, but download was 5Mbps. This is me 1-2
> meters from the router. Load was never more than 0.33. (I can share the
> results of people are interested).
One set of parameters worth fiddling with are the defaults for aggregation
in /usr/sbin/debloat which historically have been set very low for the best
balance of latency and performance.
Presently those are set to:
["qlen_vo"] = 2,
["qlen_vi"] = 4,
["qlen_be"] = 12,
["qlen_bk"] = 12,
change it to
["qlen_vi"] = 12,
["qlen_be"] = 128,
["qlen_bk"] = 128,
Your bandwidth should go up (unless there's a genuine problem
elsewhere), and your latency go to hell.
Another (better) idea is to use a better filter (problem in creating
such noted in an earlier email) that
only sorts on destination ips, with a bigger quantum. I haven't had
any success in creating that filter.
That +
I have long thought that for wifi, a quantum of 1514, or double or
treble that, was a better idea than the current defaults, *given the
underlying driver infrastructure*, and NOT in the presence of
wireless-g.
change this to something else
["CODEL_LL_QUANTUM"] = 300
then you can run
IFACE=sw00 QMODEL=fq_codel_ll /usr/sbin/debloat # for 2.4ghz
(you can also fiddle with all of these params on the command line
qlen_vi=12 qlen_be=64 qlen_bk=64 IFACE=sw00 QMODEL=fq_codel_ll /usr/sbin/debloat
A third, if you are running linux on the client, is to run fq_codel on it's
wifi interfaces via the debloat script as well. There's tons of latency
hidden in everybody's wifi drivers, and part of your problem is
coming from that.
But the up/down ratio problem you are seeing is pretty real.
>
> After a full power cycle, wifi isn't coming up at all.
The channel you selected is not legal in country "FR". (I didn't know if any
5ghz was legal yet at all in FR(?))
> =====
>
> How I got here:
>
>
> I'm in France, and had dutifully set my unit with the FR country code when
> setting up CeroWRT. I had noticed some odd latencies (periodic 100-200ms
> latency every 10-20 seconds over wifi) on the 5GHz network. The router was
> on channel 36, and I wanted to move it up to the far-upper ranges, so I
> tried to specify a "custom" channel to do so (140). This was the channel I
> thought I had been using with stock (Netgear) firmware.
Well, it's rejected by the registration database.
http://wireless.kernel.org/en/developers/Regulatory
arguably the gui should reject attempts to select channels not in the database.
140 isn't legal in the US either, so far as I recall.
you should definitely also have a consistent country code per radio.
> Wifi didn't come back up after applying the changes, and the luci interface
> seemed to be tripping up over stuff that it was reading out of the
> configuration files.
>
> I ssh'd in via ethernet, and fixed up the configurations by hand.
>
> Except the driver is still reporting that the 5GHz network won't kick into
> 802.11n modes, and won't use HT40. It seems to be sure it's configured for
> it, but isn't using it.
Might be being rejected as before.
>
> Further, digging into the rc_stats files with the minstrel speeds, I found
> some very odd data (not what I was expecting to see:
>
> (laptop, which can do 2x2 HT40)
> rate throughput ewma prob this prob this succ/attempt success
> attempts
> D 6 6.0 99.9 100.0 2( 2) 65
> 65
> 9 0.0 0.0 0.0 0( 0) 0
> 0
> 12 2.9 25.0 100.0 0( 0) 1
> 1
> 18 4.3 25.0 100.0 0( 0) 1
> 1
> 24 5.6 25.0 100.0 0( 0) 1
> 1
> A P 36 32.4 99.9 100.0 0( 0) 51
> 51
> C 48 10.4 25.0 100.0 0( 0) 1
> 1
> B 54 11.5 25.0 100.0 0( 0) 1
> 1
>
> Total packet count:: ideal 53 lookaround 7
>
> (AppleTV, 1x1 HT20)
> root at cerowrt:/sys/kernel/debug/ieee80211/phy1/netdev:sw10# cat
> stations/58\:55\:ca\:51\:b5\:4b/rc_stats
> rate throughput ewma prob this prob this succ/attempt success
> attempts
> 6 3.5 57.8 100.0 0( 0) 6
> 6
> 9 3.9 43.7 100.0 0( 0) 2
> 2
> 12 5.1 43.7 100.0 0( 0) 2
> 2
> 18 10.0 57.8 100.0 0( 0) 3
> 3
> D 24 13.1 57.8 100.0 0( 0) 3
> 3
> C 36 14.2 43.7 100.0 0( 0) 2
> 2
> B 48 18.2 43.7 100.0 0( 0) 2
> 2
> A P 54 46.2 99.9 100.0 1( 1) 348
> 367
>
> Total packet count:: ideal 331 lookaround 37
>
> Whereas what I'm seeing for the 2.4GHz radio is:
>
> root at cerowrt:/sys/kernel/debug/ieee80211/phy0/netdev:sw00/stations# cat
> 10\:9a\:dd\:30\:96\:34/rc_stats
> type rate throughput ewma prob this prob retry this
> succ/attempt success attempts
> CCK/LP 1.0M 0.7 100.0 100.0 0
> 0( 0) 2 2
> CCK/SP 2.0M 0.0 0.0 0.0 0
> 0( 0) 0 0
> CCK/SP 5.5M 0.0 0.0 0.0 0
> 0( 0) 0 0
> CCK/SP 11.0M 0.0 0.0 0.0 0
> 0( 0) 0 0
> HT20/LGI MCS0 5.6 100.0 100.0 1
> 0( 0) 2 2
> HT20/LGI MCS1 0.0 0.0 0.0 0
> 0( 0) 0 0
> HT20/LGI MCS2 0.0 0.0 0.0 0
> 0( 0) 0 0
> HT20/LGI MCS3 0.0 0.0 0.0 0
> 0( 0) 0 0
> HT20/LGI MCS4 0.0 0.0 0.0 0
> 0( 0) 0 0
> HT20/LGI MCS5 30.3 100.0 100.0 5
> 0( 0) 1 1
> HT20/LGI t MCS6 32.5 100.0 100.0 5
> 0( 0) 11 11
> HT20/LGI T P MCS7 35.0 100.0 100.0 5
> 6( 6) 34 34
>
> Total packet count:: ideal 45 lookaround 3
> Average A-MPDU length: 1.3
>
>
> And here are radio blocks from the current /etc/config/wireless:
>
> config wifi-device 'radio1'
> option type 'mac80211'
> option macaddr '28:c6:8e:bb:9a:49'
> list ht_capab 'SHORT-GI-40'
> list ht_capab 'TX-STBC'
> list ht_capab 'RX-STBC1'
> list ht_capab 'DSSS_CCK-40'
> option txpower '17'
> option distance '25'
> option channel '48'
> option country 'US'
>
> config wifi-device 'radio0'
> option type 'mac80211'
> option hwmode '11ng'
> option macaddr '28:c6:8e:bb:9a:47'
> option htmode 'HT20'
> list ht_capab 'SHORT-GI-40'
> list ht_capab 'TX-STBC'
> list ht_capab 'RX-STBC1'
> list ht_capab 'DSSS_CCK-40'
> option txpower '26'
> option country 'FR'
> option distance '15'
> option channel 'auto'
>
> ======
>
> Some notes after having repaired the situation:
>
> - The pci paths to the radios was missing from /etc/config/wireless, that's
> the only thing that I saw that seemed grossly out of place.
>
> - Back up and running, and yes, it's much happier, now. Over wifi I get
> 60-70Mbps upload and ~40Mbps download (running rrul). Latency sucks. Wifi
> has some ugly bufferbloat. (although these results are somewhat in question
> when the router has a 1m load average over 5.0...)
>
> - Enabling all the SQM features I was having previously also considerably
> cleaned up wifi performance. It's more balanced, but still not nearly as
> balanced as I see on gigabit ethernet.
>
>
>
> -Aaron
>
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> Cerowrt-devel at lists.bufferbloat.net
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>
--
Dave Täht
Fixing bufferbloat with cerowrt: http://www.teklibre.com/cerowrt/subscribe.html
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