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

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Message-ID: <492C55FC.2040506@free.fr>
Date:	Tue, 25 Nov 2008 20:46:04 +0100
From:	Benoit PAPILLAULT <benoit.papillault@...e.fr>
To:	Felix Fietkau <nbd@...nwrt.org>
CC:	Maxim Levitsky <maximlevitsky@...il.com>,
	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, Johannes Berg <johannes@...solutions.net>
Subject: Re: [ath5k-devel] Unusually low speeds with ath5k and iwl3945

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Felix Fietkau a écrit :
> While reading the code for calculating the frame duration, i noticed
> something odd: It doesn't seem to be taking into account the short
> vs long preamble distinction for ERP rates. IMHO this might be causing
> issues like this. I've seen similar behaviour a long time ago when testing
> iwl3945 against a Broadcom AP with exactly the same throughput drop (500-
> 600 kbits/s).
> When I analyzed the problem with an extra monitor mode card, I found out
> that the throughput drop is caused by a huge number of retransmissions,

In the test I've done, there was no retransmission at all (no
duplicates). I don't save a capture file, so I cannot tell for sure.

What is the code computing frame duration you are referring to? How it
could affect the hardware behavior?

> and if I remember correctly (I didn't look for this specifically back then),
> the retransmissions went down the rate scaling table until they hit the
> first non-ERP rate and that one worked on the first try.
> 
> Johannes, does that sound like a probable cause? If so, it should be easy
> to fix.
> 
> - Felix
> 

Regards,
Benoit
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