wpa_supplicant seems to prefer 2.4GHz over 5GHz

[John Frankish]

> > Ref: https://bugzilla.kernel.org/show_bug.cgi?id=175401
> > 
> That does not include wpa_supplicant debug log showing the BSS selection step.
> You would need to run wpa_supplicant without the -B command line argument to allow
> the log to continue through the connection.
> 
OK done - see https://bugzilla.kernel.org/show_bug.cgi?id=175401 (with wpa_supplicant-2.6)

> > Does anybody know why wpa_supplicant seems to prefer 2.4GHz to 5GHz?
> > 
> It should not; quite the opposite.. 5 GHz is preferred for the connection.
> That said, it looks like you are using an older version of wpa_supplicant.
> I would recommend re-running this with the current hostap.git snapshot or
> at least the last released version and providing the debug log from wpa_supplicant
> if you are still seeing the 2.4 GHz BSS being preferred.
> 
The latest version appears to be 2.6, so I compiled that, but there was no change.

> > What does wpa_supplicant use to decide which frequency to connect to?
> > 
> If you have BSSs from the same ESS (i.e., APs with same SSID) on multiple channels,
> wpa_supplicant tries to estimate the expected reliability and throughput of the connection
> through each available BSS and select the one that is likely to result in best connection.
> This determination is also taking into account the likelihood of less interference on the
> 5 GHz band and giving higher priority to it.
> 
I tried with a separation of less than 2 metres to the WAP, in which case it connects at 5GHz.

This been said, if I force the 5GHz band at the previous distance (ten metres with a structural wall in between), the throughput (measured with iperf) appears to be significantly faster than if I leave wpa_supplicant to choose the 2.4GHz band.