From mboxrd@z Thu Jan 1 00:00:00 1970 Return-path: Received: from mx1.redhat.com ([209.132.183.28]:34507 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1758132Ab3DAOvv (ORCPT ); Mon, 1 Apr 2013 10:51:51 -0400 Message-ID: <1364827975.3059.1.camel@dcbw.foobar.com> (sfid-20130401_165155_630486_43EAADF3) Subject: Re: [RFC V2] cfg80211: introduce critical protocol indication from user-space From: Dan Williams To: Ben Greear Cc: Johannes Berg , Arend van Spriel , Adrian Chadd , Felix Fietkau , linux-wireless@vger.kernel.org Date: Mon, 01 Apr 2013 09:52:55 -0500 In-Reply-To: <5154D286.4040001@candelatech.com> References: <1364472669-5629-1-git-send-email-arend@broadcom.com> <1364487476.10397.23.camel@jlt4.sipsolutions.net> <5154B347.9080904@broadcom.com> <1364506118.10397.29.camel@jlt4.sipsolutions.net> <1364510577.3226.7.camel@dcbw.foobar.com> <1364510646.10397.81.camel@jlt4.sipsolutions.net> <1364511671.3226.22.camel@dcbw.foobar.com> <5154D286.4040001@candelatech.com> Content-Type: text/plain; charset="UTF-8" Mime-Version: 1.0 Sender: linux-wireless-owner@vger.kernel.org List-ID: On Thu, 2013-03-28 at 16:30 -0700, Ben Greear wrote: > On 03/28/2013 04:01 PM, Dan Williams wrote: > > On Thu, 2013-03-28 at 23:44 +0100, Johannes Berg wrote: > >> On Thu, 2013-03-28 at 17:42 -0500, Dan Williams wrote: > >> > >>>> Well, you can do DHCP a second or so, I'd think? And EAPOL much quicker, > >>>> of course. I don't really see any reasonable minimum time? We might want > >>>> to enforce a max though, maybe. > >>> > >>> Not quite. A lot is dependent on the server itself, and I've had users > >>> on university and corporate networks report it sometimes takes 30 to 60 > >>> seconds for the whole DHCP transaction to complete (DISCOVER, REQUEST, > >>> OFFER, ACK). Sometimes there's a NAK in there if the server doesn't > >>> like your lease, which means you need another round-trip. So in many > >>> cases, it's a couple round-trips and each of these packets may or may > >>> not get lost in noisy environments. > >> > >> Oh, yes, of course. However, we're talking about optimising the good > >> cases, not the bad ones. Think of it this way: if it goes fast, we > >> shouldn't make it slow by putting things like powersave or similar in > >> the way. If it's slow, then it'll still work, just slower. But when > >> "slower" only means a few hundred milliseconds, it doesn't matter if > >> everything takes forever (30-60 secs) > > > > True, but at least 4 or 5 seconds is the minimum time I'd recommend here > > for DHCP. > > Couldn't dhcp just turn off the critical protection as soon as it is done? > > Then, you only need to worry about the max time allowed. Yes, that's really what I meant. 4 - 5 seconds is the "best worst-case scenario", clearly when a lease is acquired the critical protection would be turned off by the connection manager. But if something doesn't turn it off, and the 802.11 stack needs a timeout value, I would suggest 4 or 5 seconds for that. Dan > Also, you would probably need to enforce in the kernel that only > x out of y time in any given period can be locked, otherwise lots > of different dhclient processes (perhaps erroneously spawned..or > running on lots of different VIFs) could basically disable scanning > or channel changes... > > Thanks, > Ben >