linux-kernel - Re: many "changed bandwidth, new config is" messages in the log

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Message-ID: <1480000334.4388.2.camel@sipsolutions.net>
Date:   Thu, 24 Nov 2016 16:12:14 +0100
From:   Johannes Berg <johannes@...solutions.net>
To:     Michal Hocko <mhocko@...nel.org>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        linux-wireless <linux-wireless@...r.kernel.org>
Subject: Re: many "changed bandwidth, new config is" messages in the log

On Thu, 2016-11-24 at 15:07 +0000, Michal Hocko wrote:

> I have only now managed to move to 4.9-rc5 (from 4.8) and started
> seeing quite a lot of following messages
> "
> [  346.612211] wlan0: AP c0:4a:00:f1:48:f2 changed bandwidth, new
> config is 2472 MHz, width 1 (2472/0 MHz)
> [  352.655929] wlan0: AP c0:4a:00:f1:48:f2 changed bandwidth, new
> config is 2472 MHz, width 2 (2462/0 MHz)
> "

I don't think these messages are new in any way. checking ... nope,
it's been around that way since 3.9 :-)

> It always seems to be changing width from 1 -> 2 and back

Makes sense, that's 20 MHz <-> 40 MHz.

Did you buy a new device that says it's 40 MHz incompatible or
something? Or perhaps one of your neighbors did ... Or something is
causing interference that makes the AP switch around.

> $ dmesg | grep "changed bandwidth" | wc -l
> 42
> in 13 minutes of uptime. I have noticed this came in via 30eb1dc2c430
> ("mac80211: properly track HT/VHT operation changes").

Right, but that went into 3.9 :-)

> Is this something to be worried about?

Not at all. I suppose we could make this a debug message though, it's
not super useful when it happens OK (sometimes it causes disconnections
when we can't support the new mode, which is more relevant).

johannes