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Message-ID: <1580398006.26012.81.camel@gmail.com>
Subject: Re: Strange performance issue when using two devices at once
From:   Marlon Smith <marlon.smith10@gmail.com>
To:     Jean-Pierre TOSONI <jp.tosoni@acksys.fr>,
        "linux-wireless@vger.kernel.org" <linux-wireless@vger.kernel.org>
Date:   Thu, 30 Jan 2020 10:26:46 -0500
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On Thu, 2020-01-30 at 14:55 +0000, Jean-Pierre TOSONI wrote:
> Maybe you need to put some distance between the 3 devices.
> We experienced this kind of problem on radios close to each other
> (around 10cm).
> It was due to radio signals inducing themselves in the PCB of another
> nearby radio, causing the other radio to badly transmit and receive.
> 
> > 
> > -----Message d'origine-----
> > De : linux-wireless-owner@vger.kernel.org [mailto:linux-wireless-ow
> > ner@vger.kernel.org] De la part de
> > Marlon Smith
> > Envoyé : mercredi 29 janvier 2020 19:40
> > À : linux-wireless@vger.kernel.org
> > Objet : Strange performance issue when using two devices at once
> > 
> > Hi everyone,
> > 
> > I have two RT5370 devices connected to the same access point. Both
> > devices are very slow, but the instant I disconnect one device, the
> > other speeds up by a factor of 10.
> > 
> > The really strange part is that one device will perform slowly even
> > if
> > the other device is basically idle! I've confirmed this with a
> > packet
> > sniffer.
> > 
> > I've been trying to do some debugging, and I've found that when
> > both
> > devices are connected to the access point, they report a large
> > number
> > of duplicate frames. I added some debug output
> > in ieee80211_rx_h_check_dup() to confirm that this only happens
> > while
> > both devices are connected. The packet sniffer also shows a large
> > number of retries while this is occurring.
> > 
> > Using backports 5.3-rc4 for this, but also tested on 4.14-rc2.
> > 
> > I did post about this previously on this mailing list (RT5370
> > performance issues), but I thought I'd post again with this new
> > information and more descriptive title. I'm a little bit stuck on
> > this
> > for a while now, so any ideas are much appreciated.
> > 
> > Thanks!
> > 
> > Marlon

Thanks for the reply Jean-Pierre. I just discovered this morning that
if I change the MAC address of one of the devices, they both perform
well. So I'm wondering if it is a driver issue.

However I will keep this in mind, as I often do have multiple devices
together in close proximity.