Return-path: Received: from mgw-da01.ext.nokia.com ([147.243.128.24]:18644 "EHLO mgw-da01.nokia.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751131Ab1AQMm3 (ORCPT ); Mon, 17 Jan 2011 07:42:29 -0500 Subject: Re: [PATCH] wl12xx: Increase scan channel dwell time for passive scans From: Juuso Oikarinen To: "ext Kahn, Gery" Cc: coelho@ti.com, linux-wireless@vger.kernel.org In-Reply-To: References: <1295263943-32110-1-git-send-email-juuso.oikarinen@nokia.com> Content-Type: text/plain; charset="UTF-8" Date: Mon, 17 Jan 2011 14:42:20 +0200 Message-ID: <1295268140.18570.128.camel@wimaxnb.nmp.nokia.com> Mime-Version: 1.0 Sender: linux-wireless-owner@vger.kernel.org List-ID: On Mon, 2011-01-17 at 14:33 +0200, ext Kahn, Gery wrote: > Does it worth to have different value for 5GHz? > I guess the 100ms value benefits 2.4GHz passive scanning as well, does it not? In 2.4GHz band there are usually very few channels passive scanned (mostly channels 12 and 13 in the 00 region) so the cost of this increased wait time is quite little. -Juuso > On Mon, Jan 17, 2011 at 13:32, wrote: > > From: Juuso Oikarinen > > > > The passive scan channel dwell time currently used is 30ms-60ms. A typical > > beacon interval for AP's is 100ms. This leads to a ~30% worst-case probability > > of finding an AP via passive scanning. > > > > For 5GHz bands for DFS frequencies passive scanning is the only scanning > > option. Hence for these, the probability of finding an AP is very low. > > > > To fix this, increase the passive channel scan dwell times (also the early > > leave value, as 5GHz channels are still typically very silent.) Use a value > > of 100ms, because that covers most typical AP configurations. > > > > Based on testing the probability of finding an AP (102.4ms beacon interval) on > > a single scan round are as follows (based on 100 iterations): > > > > dwell min/max (ms) | probability > > ---------------------+------------ > > 30/60 | 35% > > 60/60 | 56% > > 80/80 | 77% > > 100/100 | 100% > > > > Total scan times now and after the change: > > > > Region | Before (s) | After (s) > > -------+------------+---------- > > 00 | 0.77 | 1.48 > > FI | 0.95 | 2.01 > > US | 0.91 | 1.76 > > > > Signed-off-by: Juuso Oikarinen > > ---