netdev - Re: BQL crap and wireless

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Date:	Fri, 2 Sep 2011 15:03:02 -0700
From:	"Luis R. Rodriguez" <mcgrof@...il.com>
To:	"John W. Linville" <linville@...driver.com>
Cc:	Jim Gettys <jg@...edesktop.org>,
	Andrew McGregor <andrewmcgr@...il.com>,
	Adrian Chadd <adrian@...ebsd.org>,
	Tom Herbert <therbert@...gle.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 Thu, Sep 1, 2011 at 7:13 AM, John W. Linville <linville@...driver.com> wrote:
> On Wed, Aug 31, 2011 at 01:50:48PM -0700, Luis R. Rodriguez wrote:
>> On Wed, Aug 31, 2011 at 6:28 AM, Jim Gettys <jg@...edesktop.org> wrote:
>
>> > such as wireless, or even possibly modern broadband with
>> > PowerBoost, classic RED or similar algorithms that do not take the
>> > buffer drain rate cannot possibly hack it properly.
>>
>> Understood, just curious if anyone has tried a Minstrel approach.
>
> FWIW, eBDP and the related algorithms from Tianji Li's paper are
> philosophically similar to minstrel.

Oh look at that, awesome!!!

>  They depend on measuring recent
> conditions and modifying the current queue length accordingly.
>
>        http://www.hamilton.ie/tianji_li/buffersizing.pdf
>
> The hack I added in debloat-testing is based on my understanding
> of eBDP.  It timestamps the SKBs when they are handed to the driver
> for Tx and then checks the timestamp when the SKB is orphaned.  It is
> a bit crude and is an abuse of the skb_orphan API.

Neat!

>  Also while it
> accounts for the 802.11e queues separately, it doesn't account for
> 802.11n aggregation.

I see..

>  Still, it seems to improve latency w/o hugely
> impacting throughput in at least some environments -- YMMV!

Sweet dude. For aggregation it seems the way to go is to get some
helpers as Andrew has suggested. Andrew, can you elaborate a little on
that? If feasible, then maybe then we can add it to the TODO list
page:

http://wireless.kernel.org/en/developers/todo-list

and when one of us gets to it, we get cranking on it.

  Luis
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