Re: [PATCH v2 2/4] knownnetworks: sort known frequencies by BSS rank

[James Prestwood <prestwoj@gmail.com>]

Hi Denis,

On 1/24/24 10:10 AM, Denis Kenzior wrote:
> Hi James,
>
> On 1/24/24 07:39, James Prestwood wrote:
>> Currently a quick scan uses the entire known frequency list so
>> ordering really doesn't matter but improvements will be made here
>> to make quick scans "quicker" for large network deployments (with
>> many known frequencies).
>>
>> To prepare for this the known frequency list has been changed to
>> be sorted by BSS rank rather than most recently seen. This makes
>> a lot more sense because IWD should prefer to scan frequencies
>> that had higher ranked BSS's, not just frequencies that were scanned
>> last on the most recent scan.
>
> Interesting.  I definitely agree with the argument for treating 
> frequencies with higher-ranked candidates as preferred, but I'm not 
> sure that directly basing the frequency preference on the bss rank is 
> the right thing to do.  A client might start right under an AP, 
> ranking it quite high, but then rapidly move away where no APs exist 
> on this frequency.  So you end up always scanning the original AP's 
> frequency.  Some sort of temporal rank decay would be needed?
Yeah, I see your point...
>
> Perhaps an easier way to accomplish this would be to add known 
> frequencies in reverse bss->rank sorted order.  That way last seen 
> frequency with best ranked BSS would be first?

I'm not sure I understand, how would this be any different than just 
reversing the list I already have? Or are you saying sort by both rank 
and last seen? Essentially have the list segmented into chunks of 
frequencies found with prior scans:

[Last Scan] [N - 1] [N - 2] [ etc ]

And if a duplicate is found, move it to the front, sorted by rank?

>
> Do note however that the quick scan approach is really meant for 
> smallish networks, to cut down scanning time when moving between Home 
> / Office location for example.  It works surprisingly well, but might 
> not be appropriate for rapid roaming in a large network.
Exactly, e.g. with 50 APs (assuming you've seen them all) a "quick" scan 
takes 5 seconds.
>
>>
>> As far as the disk sync goes the ranking is not included, but
>> ordering is. This really isn't a limitation because when IWD starts
>> up there isn't any guarantee its in the same physical location so
>> old scan ranks are likely not valid anymore. The first set of scans
>> will begin replacing the frequencies loaded from disk.
>> ---
>>   src/knownnetworks.c | 16 ++++++++++++++--
>>   src/knownnetworks.h |  1 +
>>   2 files changed, 15 insertions(+), 2 deletions(-)
>>
>
> Regards,
> -Denis
>