Differences between Atheros virtual interfaces (ath0, etc) and multiple physical ones

Question

I gather that Atheros WiFi cards potentially create multiple virtual interfaces, named ath0, ath1..

Can't find any concise information about how these operate compared to multiple physical devices when bridged or operated independently (STA, AP), etc.
It can work (bridge example), but I'd like to know what to expect of such a setup, performance/stability/capability-wise.

I'm expecting information such as "All the interfaces must operate on the same wireless channel" (can't find reference for that one).

Answer 1

Atheros cards are not the only ones on which you can build multiple interfaces. You can obtain that info from your own card by menas of iw list, search the output for this section (output for my card, an Intel 7265):

Supported interface modes:
                 * IBSS
                 * managed
                 * AP
                 * AP/VLAN
                 * monitor
                 * P2P-client
                 * P2P-GO
                 * Unknown mode (10)
        software interface modes (can always be added):
                 * AP/VLAN
                 * monitor
        valid interface combinations:
                 * #{ managed } <= 1, #{ AP, P2P-client, P2P-GO } <= 1, #{ Unknown mode (10) } <= 1,
                   total <= 3, #channels <= 2

This shows (among other things) that my card can be put into managed (the regular client) and AP (=access point) mode, and that the two can be combined, provided I use at most two channels. So, no, it is not necessary that

All the interfaces must operate on the same wireless channel

You create virtual interfaces as follows:

service network-manager stop
iw phy phy0 interface add wlan0 type station
iw phy phy0 interface add wlan1 type __ap
service network-manager start

and you delete them as

iw dev wlan1 del

As for the performance, virtual interfaces are just normal interfaces, unless you use them in combination, in which case having to shift between different channels, or having to share a single channel, cuts their throughput by (roughly) a factor of 1/N, where N is the number of interfaces on the same physical device.