Return-path: Received: from mail-pz0-f46.google.com ([209.85.210.46]:63388 "EHLO mail-pz0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932738Ab2F1KCB (ORCPT ); Thu, 28 Jun 2012 06:02:01 -0400 Received: by dady13 with SMTP id y13so2661889dad.19 for ; Thu, 28 Jun 2012 03:02:00 -0700 (PDT) MIME-Version: 1.0 In-Reply-To: <1340875996.4491.29.camel@jlt3.sipsolutions.net> References: <1340640308.27437.16.camel@jlt3.sipsolutions.net> <1340707305.14634.9.camel@jlt3.sipsolutions.net> <1340795869.11012.12.camel@jlt3.sipsolutions.net> <1340807890.11012.43.camel@jlt3.sipsolutions.net> <1340810735.11012.44.camel@jlt3.sipsolutions.net> <1340875996.4491.29.camel@jlt3.sipsolutions.net> From: Arik Nemtsov Date: Thu, 28 Jun 2012 13:01:45 +0300 Message-ID: (sfid-20120628_120209_201034_5B199F3C) Subject: Re: mac80211 auth/assoc in multi-channel scenarios To: Johannes Berg Cc: Eliad Peller , linux-wireless Content-Type: text/plain; charset=ISO-8859-1 Sender: linux-wireless-owner@vger.kernel.org List-ID: On Thu, Jun 28, 2012 at 12:33 PM, Johannes Berg wrote: > On Wed, 2012-06-27 at 20:05 +0300, Arik Nemtsov wrote: > >> > Yeah, that was one of the other options I considered in my original >> > email ... but this call must be able to sleep, and the TX processing in >> > mac80211 cannot sleep, so unless we bypass all processing (which seems >> > wrong) that would be rather difficult to implement. >> >> Good point. But another race to consider the the >> multi-channel/multi-vif scenario, where the driver already has a lot >> of packets queued up, so the time will expire before we get a chance >> to Tx. Again this is not a problem in practice (since it's the VO ac). > > If the vif is on a different channel, the driver really should assign it > different queues and then there shouldn't be much queued up, right? > Also, if you really have >100ms latency on your queues, you have a major > problem anyway I'd think? Yea. It's all only theoretical :) > >> How about somehow requiring a multi channel driver to give always >> Tx-ack? That will mean we can abandon the retry timers, and rely on >> the driver to give an answer within a reasonable time. > > That doesn't mean we can abandon the retry timers though? Then again, > maybe it does, we could start the timer only when we get the status > information I guess? I'm not really sure why the assoc timers are there now. If it's because we want to be sure we gave the peer a chance to respond, well the Tx-ack already gives us that. Waiting any longer won't help. Or does waiting in general before the next Tx help with something? (clear temporary congestion etc). > > I'm not sure I'd want to *require* this, but it sounds like a good thing > we could do to address this possible race for drivers that do support > reliable status reports? Yea. And then, if all current multi-channel drivers support Tx-ack, we can skip implemeting tx_sync.