On Thu, 2009-05-14 at 21:06 +0200, Johannes Berg wrote: > On Thu, 2009-05-14 at 14:54 -0400, Dan Williams wrote: > > > Libertas splits scans up into 3 parts with a short return to the > > operating channel between each part. There's nothing that requires > > cfg80211 for that to work... > > Yeah that was my idea too, just return to the operating channel after > having scanned a channel or two and wait for the next beacon, and > possibly receive traffic if indicated in that beacon. It takes a bit of > synchronisation and isn't easy to implement, but it's definitely > possible. > > > The problem here is that at any time an application (say, wifi location > > app) could ask for the list of access points. If you don't scan > > periodically, all APs other than your associated AP (and others on the > > same channel) will gradually drop off because their beacons are > > received. Hard to wifi position or get area statistics if there's only > > one AP in the list. > > The other thing we should do is bump the AP list timeout, I think -- 10 > seconds is very small. But then again we really need such apps to query > NM anyway. > > > Secondarily, scanning is a tradeoff between better roaming latency and > > continuous high throughput. If you don't scan, you have no idea what's > > around, and when you move and the current AP becomes marginal, you > > *have* to take the hit no matter what, so you can scan and find a new AP > > to associate with. > > Yeah, that too. > > > I would have though that the periodic scanning would be more of an > > annoyance when doing VOIP or SSH other latency sensitive tasks, but when > > just downloading a file, a few second drop in transfer rate gets lost in > > the bucket in the grand scheme of things. > > ssh isn't too bad, at least not after I fixed the timings... before I > got very annoyed with ar9170. OTOH with VoIP it would suck to have a > small hiccup every 2 minutes -- maybe then we should postpone > indefinitely and only do it if the signal strength fluctuates? If there was a reliable mechanism to figure out whether there was a certain QoS level of traffic flowing through the card, this would be easier to do automatically. AFAIK all the APIs these days are socket-based, and that doesn't help us get from app -> interface without a lot of intermediate steps. How does mac80211 figure out what to put into each of the 4 buckets for wifi QoS / WMM? Dan -- To unsubscribe from this list: send the line "unsubscribe linux-wireless" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
