Missing scan results with SCAN_FLAG_COLOCATED_6GHZ set (Ath11k/WCN6855)

Missing scan results with SCAN_FLAG_COLOCATED_6GHZ set (Ath11k/WCN6855)

[James Prestwood]

Hi,

I've noticed that when setting the colocated flag much of the scan 
results are not appearing when they should be. This was seen in a large 
warehouse where our network/SSID was using only the 6ghz band. There 
were other networks on 2.4/5ghz though, which maybe is having some 
effect, but those networks are not broadcasting on 6ghz.

This first came to my attention when the majority of our clients were 
experiencing horrible signal quality. Upon looking at the logs and 
nl80211 messages to the kernel IWD was issuing both limited 6ghz scans 
as well as full spectrum scans and only showing a few 6ghz results, like 
1-2 BSS's which should not have been the case. I was able to scan 
manually using "iw scan" and I saw all the expected BSS's. I isolated it 
to the fact that IWD was setting the SCAN_FLAG_COLOCATED_6GHZ and 
removing that flag resulted in all the BSS's showing up in scan results. 
Note, that with or without the flag all the 2.4/5ghz BSS's were showing 
up without a problem, it seems completely isolated to the 6ghz band.

The NEW_SCAN_RESULTS event was indicating the kernel had scanned all the 
expected frequencies we were asking to scan, but the results were mostly 
empty for 6ghz. Only ever the connected BSS would show up and 
_sometimes_ another BSS, but generally not.

I'm trying to read through the code associated with the COLOCATED flag, 
but its not exactly intuitive (to me at least). I'm not sure if this is 
something with mac80211 or at the driver level. I really don't have 
anything to compare it to as ath11k is the only hardware available at 
this warehouse with many APs around.

I'm looking for some guidance on if this is expected behavior with the 
colocated flag, and if there is any concern with including it 
unconditionally on every scan. If it has unintended consequences like 
this, generally, across multiple drivers I'd like to re-think its use in 
IWD.

Thanks,

James

Re: Missing scan results with SCAN_FLAG_COLOCATED_6GHZ set (Ath11k/WCN6855)

[Ben Greear]

On 10/4/24 11:46, James Prestwood wrote:
> Hi,
> 
> I've noticed that when setting the colocated flag much of the scan results are not appearing when they should be. This was seen in a large warehouse where our 
> network/SSID was using only the 6ghz band. There were other networks on 2.4/5ghz though, which maybe is having some effect, but those networks are not 
> broadcasting on 6ghz.
> 
> This first came to my attention when the majority of our clients were experiencing horrible signal quality. Upon looking at the logs and nl80211 messages to the 
> kernel IWD was issuing both limited 6ghz scans as well as full spectrum scans and only showing a few 6ghz results, like 1-2 BSS's which should not have been the 
> case. I was able to scan manually using "iw scan" and I saw all the expected BSS's. I isolated it to the fact that IWD was setting the SCAN_FLAG_COLOCATED_6GHZ 
> and removing that flag resulted in all the BSS's showing up in scan results. Note, that with or without the flag all the 2.4/5ghz BSS's were showing up without 
> a problem, it seems completely isolated to the 6ghz band.
> 
> The NEW_SCAN_RESULTS event was indicating the kernel had scanned all the expected frequencies we were asking to scan, but the results were mostly empty for 
> 6ghz. Only ever the connected BSS would show up and _sometimes_ another BSS, but generally not.
> 
> I'm trying to read through the code associated with the COLOCATED flag, but its not exactly intuitive (to me at least). I'm not sure if this is something with 
> mac80211 or at the driver level. I really don't have anything to compare it to as ath11k is the only hardware available at this warehouse with many APs around.
> 
> I'm looking for some guidance on if this is expected behavior with the colocated flag, and if there is any concern with including it unconditionally on every 
> scan. If it has unintended consequences like this, generally, across multiple drivers I'd like to re-think its use in IWD.

I had some similar issues using hostap, and hacked it to do every 4th or so scan with that
flag set differently.  Hopefully that lets the 'fast' scan work when it can, but still lets one
scan the hard way...

Possibly there are driver concerns too, I was using Intel be200 when debugging this.

Thanks,
Ben

> 
> Thanks,
> 
> James
> 
> 

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

Re: Missing scan results with SCAN_FLAG_COLOCATED_6GHZ set (Ath11k/WCN6855)

[James Prestwood]

Hi Ben,

On 10/4/24 12:18 PM, Ben Greear wrote:
> On 10/4/24 11:46, James Prestwood wrote:
>> Hi,
>>
>> I've noticed that when setting the colocated flag much of the scan 
>> results are not appearing when they should be. This was seen in a 
>> large warehouse where our network/SSID was using only the 6ghz band. 
>> There were other networks on 2.4/5ghz though, which maybe is having 
>> some effect, but those networks are not broadcasting on 6ghz.
>>
>> This first came to my attention when the majority of our clients were 
>> experiencing horrible signal quality. Upon looking at the logs and 
>> nl80211 messages to the kernel IWD was issuing both limited 6ghz 
>> scans as well as full spectrum scans and only showing a few 6ghz 
>> results, like 1-2 BSS's which should not have been the case. I was 
>> able to scan manually using "iw scan" and I saw all the expected 
>> BSS's. I isolated it to the fact that IWD was setting the 
>> SCAN_FLAG_COLOCATED_6GHZ and removing that flag resulted in all the 
>> BSS's showing up in scan results. Note, that with or without the flag 
>> all the 2.4/5ghz BSS's were showing up without a problem, it seems 
>> completely isolated to the 6ghz band.
>>
>> The NEW_SCAN_RESULTS event was indicating the kernel had scanned all 
>> the expected frequencies we were asking to scan, but the results were 
>> mostly empty for 6ghz. Only ever the connected BSS would show up and 
>> _sometimes_ another BSS, but generally not.
>>
>> I'm trying to read through the code associated with the COLOCATED 
>> flag, but its not exactly intuitive (to me at least). I'm not sure if 
>> this is something with mac80211 or at the driver level. I really 
>> don't have anything to compare it to as ath11k is the only hardware 
>> available at this warehouse with many APs around.
>>
>> I'm looking for some guidance on if this is expected behavior with 
>> the colocated flag, and if there is any concern with including it 
>> unconditionally on every scan. If it has unintended consequences like 
>> this, generally, across multiple drivers I'd like to re-think its use 
>> in IWD.
>
> I had some similar issues using hostap, and hacked it to do every 4th 
> or so scan with that
> flag set differently.  Hopefully that lets the 'fast' scan work when 
> it can, but still lets one
> scan the hard way...
>
> Possibly there are driver concerns too, I was using Intel be200 when 
> debugging this.

Thanks for the extra info. Seems like a mac80211 quirk if its also on an 
Intel card. Long term I may just parse RNR elements in userspace and 
issue extra scans if needed.

Thanks,

James