netdev - Re: BQL crap and wireless

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Message-Id: <9BB251C1-A211-486D-A717-59149AC3A709@gmail.com>
Date:	Wed, 31 Aug 2011 09:47:19 +1200
From:	Andrew McGregor <andrewmcgr@...il.com>
To:	Jim Gettys <jg@...edesktop.org>
Cc:	Adrian Chadd <adrian@...ebsd.org>,
	Tom Herbert <therbert@...gle.com>,
	"Luis R. Rodriguez" <mcgrof@...il.com>,
	Dave Taht <dave.taht@...il.com>,
	linux-wireless <linux-wireless@...r.kernel.org>,
	Matt Smith <smithm@....qualcomm.com>,
	Kevin Hayes <hayes@....qualcomm.com>,
	Derek Smithies <derek@...ranet.co.nz>, netdev@...r.kernel.org
Subject: Re: BQL crap and wireless


On 31/08/2011, at 1:58 AM, Jim Gettys wrote:

> On 08/29/2011 11:42 PM, Adrian Chadd wrote:
>> On 30 August 2011 11:34, Tom Herbert <therbert@...gle.com> wrote:
>> 
>> C(P) is going to be quite variable - a full frame retransmit of a 4ms
>> long aggregate frame is SUM(exponential backoff, grab the air,
>> preamble, header, 4ms, etc. for each pass.)
>> 
> It's not clear to me that doing heroic measures to compute the cost is
> going to be worthwhile due to the rate at which the costs can change on
> wireless; just getting into the rough ballpark may be enough. But
> buffering algorithms and AQM algorithms are going to need an estimate of
> the *time* it will take to transmit data, more than # of bytes or packets.

That's not heroic measures; mac80211 needs all the code to calculate these times anyway, it's just a matter of collecting together some things we already know and calling the right function.

Andrew--
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