[prev in list] [next in list] [prev in thread] [next in thread] 

List:       linux-wireless
Subject:    Re: [PATCH] ath9k: apply coverage class on slottime too
From:       Mathias Kretschmer <mathias.kretschmer () fokus ! fraunhofer ! de>
Date:       2012-10-31 10:47:53
Message-ID: 509101D9.2040209 () fokus ! fraunhofer ! de
[Download RAW message or body]

On 10/30/2012 02:24 PM, Felix Fietkau wrote:
> On 2012-10-30 2:00 PM, Mathias Kretschmer wrote:
>> On 10/30/2012 01:43 PM, Felix Fietkau wrote:
>>> On 2012-10-30 1:07 PM, Simon Wunderlich wrote:
>>>> From: Mathias Kretschmer <mathias.kretschmer@fokus.fraunhofer.de>
>>>>
>>>> According to 802.11-2007 17.3.8.6 (slot time), the slot time should
>>>> be increased by 3 us * coverage class. The code only increased the
>>>> ack timeout, which is fixed by this patch.
>>>>
>>>> We have noticed in our long shot scenario that we see less collisions
>>>> with this patch.
>>> At some point I had the slot time increase in the driver, but noticed a
>>> massive throughput degradation on 10-20 km links. Leaving the slot time
>>> alone and changing only the ACK timeout fixed this. What distances did
>>> you test?
>>
>> about 11km. did you test UDP (unidirectional) or TCP (bidirectional) throughput ?
> I always use TCP, because UDP tests are too unrealistic to estimate real
> performance.

bidirectional UDP traffic (iperf or preferably mgen) is a good indicator for 
problems, because there's no flow control that backs off.  depends on the use case, 
of course.

>> The larger slot time will increase the channel access overhead which should impact
>> unidirectional throughput.
>>
>> With bidirectional traffic, the larger slottime should help to minimize collisions
>> on loaded links. Overall this seems to increase the net throughput for us,
>> especially in higher access categories (smaller backoff windows).
> When I ran the test, the throughput degradation was so big that the
> links became almost useless. It was a long time ago, so maybe this was
> caused by another bug that has been fixed since. I will run another test
> with this patch in a current version...

we will also test this again. Currently, I can't access those links.

Cheers,

Mathias

> - Felix
>

--
To unsubscribe from this list: send the line "unsubscribe linux-wireless" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
[prev in list] [next in list] [prev in thread] [next in thread]