Rate limiting AP bandwidth change messages in ieee80211_config_bw?

Rate limiting AP bandwidth change messages in ieee80211_config_bw?

[Josh Boyer]

Hi Johannes,

We've seen a handful of reports that seem to have verbose output from
the ieee80211_config_bw function in net/mac80211/mlme.c.  It looks
similar to this:

[   66.578652] wlp3s0: AP xx:xx:xx:xx:xx changed bandwidth, new config
is 2437 MHz, width 2 (2447/0 MHz)
[   68.522437] wlp3s0: AP xx:xx:xx:xx:xx changed bandwidth, new config
is 2437 MHz, width 1 (2437/0 MHz)
[   69.548353] wlp3s0: AP xx:xx:xx:xx:xx changed bandwidth, new config
is 2437 MHz, width 2 (2447/0 MHz)
[   70.568677] wlp3s0: AP xx:xx:xx:xx:xx changed bandwidth, new config
is 2437 MHz, width 1 (2437/0 MHz)
[   71.489416] wlp3s0: AP xx:xx:xx:xx:xx changed bandwidth, new config
is 2437 MHz, width 2 (2447/0 MHz)
[   72.512917] wlp3s0: AP xx:xx:xx:xx:xx changed bandwidth, new config
is 2437 MHz, width 1 (2437/0 MHz)
[   73.535866] wlp3s0: AP xx:xx:xx:xx:xx changed bandwidth, new config
is 2437 MHz, width 2 (2447/0 MHz)
[   81.777530] wlp3s0: AP xx:xx:xx:xx:xx changed bandwidth, new config
is 2437 MHz, width 1 (2437/0 MHz)
[   82.540576] wlp3s0: AP xx:xx:xx:xx:xx changed bandwidth, new config
is 2437 MHz, width 2 (2447/0 MHz)
[   94.513467] wlp3s0: AP xx:xx:xx:xx:xx changed bandwidth, new config
is 2437 MHz, width 1 (2437/0 MHz)
[   95.634855] wlp3s0: AP xx:xx:xx:xx:xx changed bandwidth, new config
is 2437 MHz, width 2 (2447/0 MHz)
[   97.474767] wlp3s0: AP xx:xx:xx:xx:xx changed bandwidth, new config
is 2437 MHz, width 1 (2437/0 MHz)
[   98.498036] wlp3s0: AP xx:xx:xx:xx:xx changed bandwidth, new config
is 2437 MHz, width 2 (2447/0 MHz)
[   99.520472] wlp3s0: AP xx:xx:xx:xx:xx changed bandwidth, new config
is 2437 MHz, width 1 (2437/0 MHz)
[  100.551344] wlp3s0: AP xx:xx:xx:xx:xx changed bandwidth, new config
is 2437 MHz, width 2 (2447/0 MHz)
[  101.571100] wlp3s0: AP xx:xx:xx:xx:xx changed bandwidth, new config
is 2437 MHz, width 1 (2437/0 MHz)
[  102.490708] wlp3s0: AP xx:xx:xx:xx:xx changed bandwidth, new config
is 2437 MHz, width 2 (2447/0 MHz)

Essentially, this looks like the AP is changing the bandwidth (and
only the width) every second or so.  Why it is doing this, I'm not
sure.  However, this doesn't seem to actually be an error case yet the
kernel logs are getting spammed with this message.

I'm wondering if we could either change this message to use sdata_dbg
instead of sdata_info, or if we could possibly ratelimit it somehow.
I'd be happy to come up with a patch for either, but I wanted to get
your feedback on it before I started.  Do you have any objections or
preference?

josh

Re: Rate limiting AP bandwidth change messages in ieee80211_config_bw?

[Johannes Berg]

On Wed, 2015-09-30 at 13:02 -0400, Josh Boyer wrote:
> Hi Johannes,
> 
> We've seen a handful of reports that seem to have verbose output from
> the ieee80211_config_bw function in net/mac80211/mlme.c.  It looks
> similar to this:
> 
> [   66.578652] wlp3s0: AP xx:xx:xx:xx:xx changed bandwidth, new config
> is 2437 MHz, width 2 (2447/0 MHz)
> [   68.522437] wlp3s0: AP xx:xx:xx:xx:xx changed bandwidth, new config
> is 2437 MHz, width 1 (2437/0 MHz)

> Essentially, this looks like the AP is changing the bandwidth (and
> only the width) every second or so.  Why it is doing this, I'm not
> sure.  However, this doesn't seem to actually be an error case yet the
> kernel logs are getting spammed with this message.
> 
> I'm wondering if we could either change this message to use sdata_dbg
> instead of sdata_info, or if we could possibly ratelimit it somehow.
> I'd be happy to come up with a patch for either, but I wanted to get
> your feedback on it before I started.  Do you have any objections or
> preference?
> 

I'm not sure ratelimiting it would even work - it's not *that* high
frequency? Not really sure though.

I think we can do either, it's not such a terribly important message as
far as I can tell.

johannes

Re: Rate limiting AP bandwidth change messages in ieee80211_config_bw?

[Johannes Berg]

> 
> I'm not sure ratelimiting it would even work - it's not *that* high
> frequency? Not really sure though.
> 
> I think we can do either, it's not such a terribly important message as
> far as I can tell.
> 

Seems like Emmanuel would like to see the message stay in some form -
perhaps we should try rate limiting it then? Could you check if that
actually works?

johannes

Re: Rate limiting AP bandwidth change messages in ieee80211_config_bw?

[Josh Boyer]

On Wed, Sep 30, 2015 at 3:04 PM, Johannes Berg
<johannes@sipsolutions.net> wrote:
>
>>
>> I'm not sure ratelimiting it would even work - it's not *that* high
>> frequency? Not really sure though.
>>
>> I think we can do either, it's not such a terribly important message as
>> far as I can tell.
>>
>
> Seems like Emmanuel would like to see the message stay in some form -

For what purpose?  Or rather, when a user sees this in their dmesg,
what are they supposed to do about it?

> perhaps we should try rate limiting it then? Could you check if that
> actually works?

I'll think on it, sure.  I was hoping sdata_dbg would be sufficient
because it's much easier, but if there's value in the message I can
look at limiting it in some fashion.

josh

Re: Rate limiting AP bandwidth change messages in ieee80211_config_bw?

[Johannes Berg]

> For what purpose?  Or rather, when a user sees this in their dmesg,
> what are they supposed to do about it?

I think the idea isn't that the user would do something, but more that
in case of performance issues, or perhaps driver/device bugs handling
the changes, or similar you'd have an indication that this happened.


> > perhaps we should try rate limiting it then? Could you check if 
> > that
> > actually works?
> 
> I'll think on it, sure.  I was hoping sdata_dbg would be sufficient
> because it's much easier, but if there's value in the message I can
> look at limiting it in some fashion.
> 

Thanks.

johannes