From: Marek Lindner <lindner_marek@yahoo.de>
To: Daniel Halperin <dhalperi@cs.washington.edu>
Subject: Re: [PATCH] mac80211: minstrel_ht should not override user supplied rts setting
Date: Sun, 29 Jan 2012 04:09:06 +0800
Cc: Felix Fietkau <nbd@openwrt.org>, linux-wireless@vger.kernel.org
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On Sunday, January 29, 2012 04:03:41 you wrote:
> On Sat, Jan 28, 2012 at 11:58 AM, Marek Lindner <lindner_marek@yahoo.de> 
wrote:
> > On Sunday, January 29, 2012 03:17:32 Daniel Halperin wrote:
> >> Adaptive RTS/CTS is important to control for interference---RTS/CTS is
> >> there so that other Wi-Fi devices know not to interfere with your
> >> flow. It may well be the case that this is not a major problem in
> >> whatever your scenario you're working, Marek, but it makes a big
> >> difference in a many bad corner cases.
> > 
> > I am very well aware of what RTS/CTS is for and I am not against using
> > it. However, having the rate algorithm overriding the user setting for a
> > specific rate is extremely hard to grasp or debug.
> > To give you an understanding where I am coming from: In our networks we
> > experienced extremely variable throughput ranging from 30Mbit/s (single
> > stream) to 0.2 Mbit/s in the next second. As you can imagine we were
> > trying to figure out what was going on. After spending some time and
> > losing hair I noticed that the RTS/CTS implementation of our driver
> > (ath9k) is buggy. Every once in a while the nodes would "battle" each
> > other with RTS/CTS packets. Strange enough for us, sometimes no RTS
> > packets were sent and sometimes they would battle. All attempts to
> > disable RTS/CTS for the mere sake of testing(!) was impossible. First I
> > thought ath9k did not properly implement the "iw rts" setting but that
> > wasn't the case. After losing more hair I realized that minstrel_ht, a
> > rate control algorithm(!), was overriding my rts settings but not
> > always(!). The only way to make RTS shut up was to apply the posted
> > patch.
> 
> Can you explain what the low-level behavior of an RTS/CTS "battle" is?
> 
> Abstractly, the behavior you're describing sounds like a buggy driver
> that doesn't obey overheard RTS or CTS packets.

I certainly can explain it but this is for another thread and unrelated to the 
points raised before.

Regards,
Marek