Return-path: Received: from xc.sipsolutions.net ([83.246.72.84]:53556 "EHLO sipsolutions.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751225AbZENTHI (ORCPT ); Thu, 14 May 2009 15:07:08 -0400 Subject: Re: Scan while TX/RX'ing a lot of data From: Johannes Berg To: Dan Williams Cc: "Luis R. Rodriguez" , linux-wireless , Aeolus.Yang@atheros.com, Senthil Balasubramanian , Gaurav.Jauhar@atheros.com In-Reply-To: <1242327298.4227.25.camel@localhost.localdomain> References: <43e72e890905141052o1f072bc5m4bc5922327617f8b@mail.gmail.com> <1242327298.4227.25.camel@localhost.localdomain> Content-Type: multipart/signed; micalg="pgp-sha1"; protocol="application/pgp-signature"; boundary="=-eVOGB4mhInuZji5uP2VU" Date: Thu, 14 May 2009 21:06:35 +0200 Message-Id: <1242327995.5799.4.camel@johannes.local> Mime-Version: 1.0 Sender: linux-wireless-owner@vger.kernel.org List-ID: --=-eVOGB4mhInuZji5uP2VU Content-Type: text/plain Content-Transfer-Encoding: quoted-printable 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? johannes --=-eVOGB4mhInuZji5uP2VU Content-Type: application/pgp-signature; name="signature.asc" Content-Description: This is a digitally signed message part -----BEGIN PGP SIGNATURE----- iQIcBAABAgAGBQJKDGu2AAoJEODzc/N7+QmajtQP/1b2jtlz+r5PGcPrCVL5QHIH H/2WpYeoYn5W9RnxzTgQiPnZ/1Glcos1hLfOhqiAEQUJX5oXh5pPl50qFrLkZ7pR 7GF1Jc3SxsXzeI4temiTvLa51cQDFfjcMhbLtfyCoEFaXNZ438/AA5I1c+fVk435 WNRyzLDEMPCq37fk9xNI/5kqtD2skL/HRNCHuDAFxvsIqUMijARxK61tVNRITSWW o1d/HOLJ6paJ6pCzKW1XoD0PBb7sHW232QhM7y2AEvOiFoD1PvBzgpD001TZgpJE fW5wvrxV7Nb4ixyzRdW3ZzM9c2u0b4WvRmYJhWsB4ksB0Nl2doqpJRz2/yhQj09h HbeRvgXU/5YSg1pSZ7SpCeZAClXs19O/++VhDqwpfHU6b76rmJm/YgsXWR7EQC66 NlbQ405zvzYD416J7aTgiZTES38+l2TQGRg6yxYl2DktwmTH7e8g+iYh/btVeaLS jXTj5gC7ywtNjNlJEvK0NmxxsbA1O2y3EX5RUS8J6paLt/CDyn4NX1Mke7dSWsTr W00tc0qtwyK92Zy8HIR+bjBZDP/pZGv6RxFsWHtGMUi7tclb0IHowzqrBCnm8zmc 5bbK3gKLzmiQSWMWympvApwViasDSKHbrCz+wSBOb97cp+Wz8LCuEeYMsDEnxUSq SWQIX6oq/gfBr+fTfl6s =FBKm -----END PGP SIGNATURE----- --=-eVOGB4mhInuZji5uP2VU--