ath9k: performance regressions / tx semi-stuck somehow

ath9k: performance regressions / tx semi-stuck somehow

[Björn Smedman]

Hi all,

I just tried out compat-wireless-2010-07-16 on AR913x (with
openwrt/trunk@r22321) and saw some weird performance problems.

First, with the default 11n HT20 AP configuration I get really good
performance on an old 11g MacBook. 16Mbps downloads limited by WAN. :)

But then I try a newer 11n MacBook and performance absolutely sucks.
2-3Mbps downloads with erratic bursts and "hangs".

So, I start to think something is wrong with 11n and reconfigure for
11g only. Then the 11g MacBook performance also sucks. The same
2-3Mbps downloads with erratic bursts and "hangs". So 11n AP and 11g
client is good, but 11g AP and 11g client sucks. Looking at the
rc_stats it seems like tx completely breaks down from time to time:

root@OpenWrt:/sys/kernel/debug/ieee80211/phy0# cat stations/00\:17\:f2\:51\:b2\:
2d/rc_stats
rate     throughput  ewma prob   this prob  this succ/attempt
success    attempts
 t   1         0.1       18.3        0.0          0( 19)         28         731
     2         0.0        0.0        0.0          0(  0)          0          18
     5.5       0.0        0.0        0.0          0(  0)          0          10
    11         0.0        0.0        0.0          0(  0)          0          14
     6         0.0        0.0        0.0          0(  0)          0          11
     9         0.0        0.0        0.0          0(  0)          0          18
    12         0.0        0.0        0.0          0(  0)          0          12
    18         0.0        0.0        0.0          0(  0)          0          16
    24         0.0        0.0        0.0          0(  0)          0          18
    36         0.1        0.4        0.0          0(  0)          2        1824
    48         0.0        0.0        0.0          0(  2)          0          16
T P 54        27.3       63.1        0.0          0(180)       4749       13896

Total packet count::    ideal 4780      lookaround 532

That's in exactly the same spot I was getting 16Mbps consistently with
AP was 11n!

Any debuging I can do to help? Bisecting is unfortunately a lot of
work on this embedded system...

/Björn

Re: [ath9k-devel] ath9k: performance regressions / tx semi-stuck somehow

[Felix Fietkau]

On 2010-07-22 12:17 AM, Björn Smedman wrote:
> Hi all,
> 
> I just tried out compat-wireless-2010-07-16 on AR913x (with
> openwrt/trunk@r22321) and saw some weird performance problems.
> 
> That's in exactly the same spot I was getting 16Mbps consistently with
> AP was 11n!
> 
> Any debuging I can do to help? Bisecting is unfortunately a lot of
> work on this embedded system...
Could you please try if the earlier version that was in OpenWrt
(2010-07-06) has the same issues?

- Felix

Re: [ath9k-devel] ath9k: performance regressions / tx semi-stuck somehow

[Björn Smedman]

2010/7/22 Felix Fietkau <nbd@openwrt.org>:
> On 2010-07-22 12:17 AM, Björn Smedman wrote:
>> Hi all,
>>
>> I just tried out compat-wireless-2010-07-16 on AR913x (with
>> openwrt/trunk@r22321) and saw some weird performance problems.
>>
> Could you please try if the earlier version that was in OpenWrt
> (2010-07-06) has the same issues?
>

Quickly flashing the builds I have on hand I came up with this small
table comparing MacBook 11g and 11n clients for various openwrt/trunk
versions:

r21960P (compat-wireless-2010-06-15): 11g = 12Mbps, 11n = 7.2Mbps
r22286 (compat-wireless-2010-07-06): 11g = 7.2Mbps*, 11n = 4.2Mbps*
r22321 (compat-wireless-2010-07-16): 11g = 12Mbps*, 11n = 2.9Mbps*

(*) Bursty / unstable performance.
(P) Some patches of my own on top of openwrt.

I realize it doesn't say very much unfortunately...

/Björn

Re: [ath9k-devel] ath9k: performance regressions / tx semi-stuck somehow

[Björn Smedman]

2010/7/23 Björn Smedman <bjorn.smedman@venatech.se>:
> 2010/7/22 Felix Fietkau <nbd@openwrt.org>:
>> On 2010-07-22 12:17 AM, Björn Smedman wrote:
>>> I just tried out compat-wireless-2010-07-16 on AR913x (with
>>> openwrt/trunk@r22321) and saw some weird performance problems.
>>>
>> Could you please try if the earlier version that was in OpenWrt
>> (2010-07-06) has the same issues?

I had some trouble reproducing this but now I feel convinced that this
performance issue was caused by interference, although I think ath9k
could do a better job in difficult radio environments.

Note how downstream throughput goes from ~55 Mbps down to around 3
Mbps. Nothing is moved in this experiment.

bjorn-smedmans-macbook-2:~ bjornsmedman$ iperf -w 256K -s
------------------------------------------------------------
Server listening on TCP port 5001
TCP window size:   256 KByte
------------------------------------------------------------
[  4] local 192.168.78.119 port 5001 connected with 192.168.78.211 port 58060
[ ID] Interval       Transfer     Bandwidth
[  4]  0.0-30.0 sec    194 MBytes  54.1 Mbits/sec
[  4] local 192.168.78.119 port 5001 connected with 192.168.78.211 port 58926
[ ID] Interval       Transfer     Bandwidth
[  4]  0.0-30.0 sec    203 MBytes  56.6 Mbits/sec
[  4] local 192.168.78.119 port 5001 connected with 192.168.78.211 port 58990
[ ID] Interval       Transfer     Bandwidth
[  4]  0.0-30.0 sec    190 MBytes  53.2 Mbits/sec
[  4] local 192.168.78.119 port 5001 connected with 192.168.78.211 port 59236
[ ID] Interval       Transfer     Bandwidth
[  4]  0.0-30.0 sec    189 MBytes  52.8 Mbits/sec
[  4] local 192.168.78.119 port 5001 connected with 192.168.78.211 port 64327

[Some interference source probably comes in here]

[ ID] Interval       Transfer     Bandwidth
[  4]  0.0-34.5 sec  5.64 MBytes  1.37 Mbits/sec
[  4] local 192.168.78.119 port 5001 connected with 192.168.78.211 port 64424
[ ID] Interval       Transfer     Bandwidth
[  4]  0.0-30.3 sec  8.06 MBytes  2.23 Mbits/sec
[  4] local 192.168.78.119 port 5001 connected with 192.168.78.211 port 64625
[ ID] Interval       Transfer     Bandwidth
[  4]  0.0-31.3 sec  13.6 MBytes  3.64 Mbits/sec


If I then switch the AP channel (from 1 to 11) performance is looking
good again:

bjorn-smedmans-macbook-2:~ bjornsmedman$ iperf -w 256K -s
------------------------------------------------------------
Server listening on TCP port 5001
TCP window size:   256 KByte
------------------------------------------------------------
[  4] local 192.168.78.119 port 5001 connected with 192.168.78.211 port 55550
[ ID] Interval       Transfer     Bandwidth
[  4]  0.0-120.0 sec    621 MBytes  43.4 Mbits/sec
[  4] local 192.168.78.119 port 5001 connected with 192.168.78.211 port 55562
[ ID] Interval       Transfer     Bandwidth
[  4]  0.0-120.0 sec    764 MBytes  53.4 Mbits/sec
[  4] local 192.168.78.119 port 5001 connected with 192.168.78.211 port 55568
[ ID] Interval       Transfer     Bandwidth
[  4]  0.0-10.0 sec  68.1 MBytes  56.9 Mbits/sec


/Björn