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

[Denis Kenzior <denkenz@gmail.com>]

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?

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?

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.

> 
> 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