linux-kernel - Re: [ath5k-devel] Unusually low speeds with ath5k and iwl3945

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Date:	Mon, 24 Nov 2008 08:34:43 +0100
From:	Benoit PAPILLAULT <benoit.papillault@...e.fr>
To:	Maxim Levitsky <maximlevitsky@...il.com>
CC:	Derek Smithies <derek@...ranet.co.nz>, ath5k-devel@...ts.ath5k.org,
	linux-wireless@...r.kernel.org, linux-kernel@...r.kernel.org,
	ipw3945-devel@...ts.sourceforge.net, wally@...blackmoor.net
Subject: Re: [ath5k-devel] Unusually low speeds with ath5k and iwl3945

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Maxim Levitsky a écrit :
> Derek Smithies wrote:
>> Hi,
>>  to verify that it is a rate control issue, there is one very simple and 
>> very practical test.
>>
>> Take both ends of your link, and set them to fixed rate, and at the rate 
>> you think it should be achieving.
>> If you can achieve significantly higher throughputs with fixed rate, you 
>> know that the rate control algorithm (or interface with rate algorithm) 
>> has failed.
>>
>> Derek.
>>
>> On Fri, 21 Nov 2008, Bob Copeland wrote:
>>
>>> On Fri, Nov 21, 2008 at 10:28:29PM +0200, Maxim Levitsky wrote:
>>>> I initially blamed iwl3945, then thought it got fixed, but now I have
>>>> ath5k, and speeds are low
>>>> and I suspect that both drivers has bugs regarding to speed.
>>> Quite possible, but both use mac80211 for rate control.  Which rate
>>> control algorithm are you using?
> Hi,
> 
> Well, iwl3945 was showing 54M all the time in iwconfig,
> also it doesn't support setting fixed rate, at least not using iwconfig.
> 
> ath5k never shows higher that 18M, and supports setting fixed rate, but if I set it to anything higher that 18M,
> speeds drop to 0Kbytes/s immediately.
> Speeds lower that 18M work, and affect throughput accordantly
> For most of tests speeds are ether 18M or lower, but then when I set them to 18M this didn't increase throughput.
>  
> iwl3945 was always at 54M
> 
> 
> 
> Best regards,
> 	Maxim Levitsky

I did a similar test here and results is very strange. AP was my good
old linksys WRT54G running an iperf server. Client was a laptop running
either ath5k or madwifi/trunk and an iperf client. Channel is 5. Both
drivers show the same behaviour.

At the beginning, throughput was very low : 500 - 600 kbit/s. Suddenly
(after few minutes), it jumps to 15 - 17 Mbit/s and then few minutes
later (let's say 10 - 20 minutes maybe), it jumps back to 500 - 600
kbit/s. Using a fixed rate has no effect.

I used my latest wireless monitoring tools and I did not saw lost of
duplicates or lost packets. The only difference was the number of
packets sent by seconds....

Looking a my syslog, I just saw few messages, unrelated in time with the
throughput going up or down. They were:
- - ath5k : unsupported jumbo
- - switching to short barker preamble
- - switching to long barker preamble

I can repeat the same test with iwl3945 as well, if needed.

Regards,
Benoît
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