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Subject: Re: Strange performance issue when using two devices at once
To:     Marlon Smith <marlon.smith10@gmail.com>,
        linux-wireless@vger.kernel.org
References: <1580323191.26012.48.camel@gmail.com>
 <2e80a485-892d-3b29-19c7-38a9caa14f4b@candelatech.com>
 <1580325769.26012.54.camel@gmail.com>
From:   Ben Greear <greearb@candelatech.com>
Organization: Candela Technologies
Message-ID: <6bcff97c-3b9b-7fa9-5101-80aca367ff84@candelatech.com>
Date:   Wed, 29 Jan 2020 11:27:17 -0800
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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


-- 
Ben Greear <greearb@candelatech.com>
Candela Technologies Inc  http://www.candelatech.com