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Message-ID: <1580330950.26012.62.camel@gmail.com>
Subject: Re: Strange performance issue when using two devices at once
From:   Marlon Smith <marlon.smith10@gmail.com>
To:     Ben Greear <greearb@candelatech.com>,
        linux-wireless@vger.kernel.org
Date:   Wed, 29 Jan 2020 15:49:10 -0500
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On Wed, 2020-01-29 at 12:01 -0800, Ben Greear wrote:
> On 1/29/20 11:48 AM, Marlon Smith wrote:
> > 
> > On Wed, 2020-01-29 at 11:27 -0800, Ben Greear wrote:
> > > 
> > > On 1/29/20 11:22 AM, Marlon Smith wrote:
> > > > 
> > > > 
> > > > On Wed, 2020-01-29 at 10:42 -0800, Ben Greear wrote:
> > > > > 
> > > > > 
> > > > > On 1/29/20 10:39 AM, Marlon Smith wrote:
> > > > > > 
> > > > > > 
> > > > > > 
> > > > > > 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.
> > > > > Out of curiosity, are both of the RT5370 used on the same
> > > > > client
> > > > > device?
> > > > > > 
> > > > > > 
> > > > > > Did you check that they have unique MAC addresses?
> > > > > > Thanks,
> > > > > Ben
> > > > > > 
> > > > > > 
> > > > > > > 
> > > > > > > 
> > > > > > > 
> > > > > > 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
> > > > > > 
> > > > They are on separate devices, although the mac addresses are
> > > > close.
> > > > 70:F1:1C:2E:AF:B4 and
> > > > 70:F1:1C:2E:AF:B6.
> > > > 
> > > > However, I have a third device 70:F1:1C:2E:AF:BB which performs
> > > > well
> > > > and does not affect the performance of the other two.
> > > > 
> > > Have you tried a different AP?
> > > 
> > > And also tried using the exact same MAC addresses configured on a
> > > different
> > > radio (like ath9k)?
> > > 
> > > Thanks,
> > > Ben
> > > 
> > > 
> > I have tried a different access point in a different environment
> > but no
> > luck. I'll see if I can configure my laptop to use one of the
> > problematic devices' mac address.
> It might be tricky to determine, but if you can notice whether one of
> your station devices
> is (block-)acking the other's frames, that would be a good clue that
> it is a station
> side bug.  A carefully inspected sniff, especially if you can put
> sniffer near one station
> and far from the other and so use RSSI as a sorting factor, should
> allow you to determine
> this.
> 
> Thanks,
> Ben
> 
> 

I'll double check this, but I believe there is very little traffic from
the second station while the first station is (slowly) transferring
data. I think that means it's not likely that one device is acking the
other's frames?

I will test this though, and the mac address spoofing, and get back to
you tomorrow.

Really appreciate the help so far, thank you!