Re: Pondering: how to improve mac80211 roaming ...

[Helmut Schaa <hschaa@suse.de>]

Am Mittwoch, 13. August 2008 14:49:15 schrieb Dan Williams:
> On Wed, 2008-08-13 at 14:26 +0200, Helmut Schaa wrote:
> > Am Dienstag, 12. August 2008 17:42:23 schrieb Jouni Malinen:
> > > On Tue, Aug 12, 2008 at 02:40:23PM +0200, Helmut Schaa wrote:
> > > > JFYI I already started to rework the existing scan code in mac80211
> > > > (software scan) to do something like background scanning:
> > > >
> > > > 1) notify current AP about leaving the channel
> > > > 2) scan one channel
> > >
> > > It might be useful to leave this "one" as a parameter to allow easy
> > > experiments with scanning more than one channel at a time to reduce
> > > latency.
> >
> > Good point.
> >
> > > Ideally, this--along the interval for background scans--could
> > > be something that is dynamically changed based on the expected traffic
> > > pattern. Whenever there is lot of data traffic being (mostly
> > > successfully) transmitted, it would be beneficial not to jump to other
> > > channels as frequently or for as long a time. If there has not been any
> > > data transmission for some time, it may be more acceptable to scan more
> > > frequently and to remain away from the operational channel for longer
> > > periods of time. Though, we should also keep in mind that background
> > > scans are going to increase power consumption on otherwise inactive
> > > situation, so setting a suitable policy for this can get quite complex.
> >
> > It might even be beneficial to cancel a currently active background scan
> > once the TX queue is filling up and report the already gathered
> > information to the user space.
>
> If that's the case, we should also then have a response to the original
> scan request (or broadcast netlink message with the original request's
> cookie) that says "scan canceled" so that the requester can handle that.

Right. Something like "The scan was canceled but here are the incomplete 
results".

Helmut