flicker-free suspend/resume on Intel [LWN.net]

flicker-free suspend/resume on Intel

Posted Mar 7, 2013 20:39 UTC (Thu) by johill (subscriber, #25196)
In reply to: flicker-free suspend/resume on Intel by raven667
Parent article: The conclusion of the 3.9 merge window

Well, yes. Although you could scan the channels in the right order, i.e. the ones that you'd expect the same network (SSID) on first. Say your corporate installation -- it's probably only going to use a handful of channels (1,6,11,36,149 or so), so if you know from "experience" that (almost) all of the APs for the network are there, you can scan those first.

But ultimately you're right, in the general case you have to scan all channels and that simply takes a while. It shouldn't be more than a few seconds since you're not connected; here it takes ~3.5 seconds to scan all the channels my card supports, but I know that it can be (much) slower depending on the device.

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flicker-free suspend/resume on Intel

Posted Mar 7, 2013 23:25 UTC (Thu) by dlang (guest, #313) [Link] (1 responses)

well, you should first check the channel you were last using, and then do the normal scan you would do if someone just gave the SSID and told you to connect to it.

flicker-free suspend/resume on Intel

Posted Mar 8, 2013 0:10 UTC (Fri) by johill (subscriber, #25196) [Link]

Yeah, that's what I suggested first (and indeed Dan has now opened a bug for to implement it in NM), however it is possible to break it down further like I was trying to describe later:

1) scan the last channel
2) scan the known channels for the last SSID
3) scan all (remaining) channels

The intermediate step only makes sense if those known channels are a relatively small subset of all channels, but with typical installations they will be. In fact, for many networks like your home network 1) and 2) will be exactly the same because you only have a single AP, but for typical enterprise networks 2) will still be better than 3).