[ath9k-devel] TX packets dropped

[ath9k-devel] TX packets dropped

[David Ehrmann]

I have an AR9220 mini PCI card (Sparklan WMIA-198n) on an Alix 3d2 board 
running OpenWrt (2.6.32.25 kernel).  I set up the radio in AP mode, give 
it encryption, then connected with another computer with an Intel 
802.11n card.  The connection wasn't reliable, so I tested it with 
iperf.  When the client sends packets, they almost all make it, but when 
the AP sends them, no more than 66% make it.  I'm trying to figure out 
what the problem could be.  It shouldn't be interference--this is in a 
5ghz band, and RX was fine.  It could be a bad pigtail or antenna, but 
I'm not sure how I can test for that.  It might be the motherboard's 
power supply, so I'm looking into how many watts it can supply (the card 
specs say it takes ~2.5 watts).  I tried forcing 802.11g mode, and the 
issue was still there, and I dropped TX power, but it didn't seem to 
affect anything.

Any ideas?  Is there a way to check stats on each antenna?

[ath9k-devel] TX packets dropped

[Brian Prodoehl]

On Sun, Nov 21, 2010 at 2:08 AM, David Ehrmann <ehrmann@gmail.com> wrote:
> I have an AR9220 mini PCI card (Sparklan WMIA-198n) on an Alix 3d2 board
> running OpenWrt (2.6.32.25 kernel). ?I set up the radio in AP mode, give
> it encryption, then connected with another computer with an Intel
> 802.11n card. ?The connection wasn't reliable, so I tested it with
> iperf. ?When the client sends packets, they almost all make it, but when
> the AP sends them, no more than 66% make it. ?I'm trying to figure out
> what the problem could be. ?It shouldn't be interference--this is in a
> 5ghz band, and RX was fine. ?It could be a bad pigtail or antenna, but
> I'm not sure how I can test for that. ?It might be the motherboard's
> power supply, so I'm looking into how many watts it can supply (the card
> specs say it takes ~2.5 watts). ?I tried forcing 802.11g mode, and the
> issue was still there, and I dropped TX power, but it didn't seem to
> affect anything.
>
> Any ideas? ?Is there a way to check stats on each antenna?

What do ping times look like between AP and client?  I'm seeing
similar behavior with OpenWrt trunk (r24043) and an AP with an AR9160
chip.  I'm having TX traffic queue up on the AP for seconds at a time,
so I'll have periods of no traffic at all, and then all the pings will
come through at once, with times of 8s, 7s, 6s, 5s, 4s, 3s, 2s, 1s,
and 1.97ms or whatever.  I have two other APs here with different
drivers and chipsets that don't exhibit this.  I don't remember seeing
this with recent builds of backfire, so maybe its a relatively recent
regression in OpenWrt.  You're running trunk, right?  What svn rev?

[ath9k-devel] TX packets dropped

[David Ehrmann]

On 11/21/2010 4:51 PM, Brian Prodoehl wrote:
> On Sun, Nov 21, 2010 at 2:08 AM, David Ehrmann<ehrmann@gmail.com>  wrote:
>> I have an AR9220 mini PCI card (Sparklan WMIA-198n) on an Alix 3d2 board
>> running OpenWrt (2.6.32.25 kernel).  I set up the radio in AP mode, give
>> it encryption, then connected with another computer with an Intel
>> 802.11n card.  The connection wasn't reliable, so I tested it with
>> iperf.  When the client sends packets, they almost all make it, but when
>> the AP sends them, no more than 66% make it.  I'm trying to figure out
>> what the problem could be.  It shouldn't be interference--this is in a
>> 5ghz band, and RX was fine.  It could be a bad pigtail or antenna, but
>> I'm not sure how I can test for that.  It might be the motherboard's
>> power supply, so I'm looking into how many watts it can supply (the card
>> specs say it takes ~2.5 watts).  I tried forcing 802.11g mode, and the
>> issue was still there, and I dropped TX power, but it didn't seem to
>> affect anything.
>>
>> Any ideas?  Is there a way to check stats on each antenna?
> What do ping times look like between AP and client?  I'm seeing
> similar behavior with OpenWrt trunk (r24043) and an AP with an AR9160
> chip.  I'm having TX traffic queue up on the AP for seconds at a time,
> so I'll have periods of no traffic at all, and then all the pings will
> come through at once, with times of 8s, 7s, 6s, 5s, 4s, 3s, 2s, 1s,
> and 1.97ms or whatever.  I have two other APs here with different
> drivers and chipsets that don't exhibit this.  I don't remember seeing
> this with recent builds of backfire, so maybe its a relatively recent
> regression in OpenWrt.  You're running trunk, right?  What svn rev?

My ping times are typically between 2ms and 5ms, but around 1 in 15 is 
more like 15ms to 50ms.  My 802.11g AP behaves roughly the same.  
Traffic could be bunching up, though.  Sometimes the console (over SSH) 
won't respond when I hit enter, but a few seconds later, all the new 
lines show up.

I'm using r23987, so it might be the same issue.

[ath9k-devel] TX packets dropped

[David Ehrmann]

I guess I got the card wrong--it's a routerboard R52N.  It uses the same 
chipset, though.  Here's what's weird: I removed the the card and put it 
on a Via Mini ITX motherboard.  I used the exact same OS and 
configuration.  My problem went away.  After making sure it wasn't a 
power supply issue, I reassembled my old configuration, and now it's 
working.  Currently, I'm seeing only 1.1% TX packet drops (and 4.5ms 
jitter).

That means that the mini PCI card could have been seated wrong, there's 
a short in a pigtail, the pigtail-card connector had problems, or 10 
feet and two walls did this.  I'm going to move it back, but if that's 
not it, this problem's really worrying because it probably involves a 
bad pigtail, I don't know which one it is, and it could happen again if 
things get bumped around enough.

[ath9k-devel] TX packets dropped

[David Ehrmann]

20 Mbps.  If I'm in TCP mode, I can get 24 Mbps.  That seems a little 
slow when the connection speed is 78Mbps.  If I drop the load to 2Mbps, 
the loss practically disappears, so I must be saturating the link.

On 11/22/2010 9:13 PM, Ranga Rao Ravuri wrote:
> What is the load on tx path ? I mean -b of iperf or equivalent in your 
> tool.
> thanks, Ranga
>
> On 11/22/2010 10:06 PM, David Ehrmann wrote:
>>   I'm seeing only 1.1% TX packet drops (and 4.5ms
>> jitter).

[ath9k-devel] TX packets dropped

[Björn Smedman]

On Tue, Nov 23, 2010 at 6:27 AM, David Ehrmann <ehrmann@gmail.com> wrote:
> 20 Mbps. ?If I'm in TCP mode, I can get 24 Mbps. ?That seems a little
> slow when the connection speed is 78Mbps. ?If I drop the load to 2Mbps,
> the loss practically disappears, so I must be saturating the link.

I'm seeing something similar on a completely different platform
(AR913x APSoC) so this can probably be considered "normal".

I don't think link saturation is a reasonable explanation though
because, as you say, rate has to be reduced significantly (an order of
magnitude) before packet loss stops. My guess is some form of race
condition on the TX queue, but that's just speculation.

/Bj?rn