Re: [PATCHv4 5/5] mac80211: add debug knobs for codel

From: Dave Taht <dave.taht@gmail.com>
To: Michal Kazior <michal.kazior@tieto.com>
Cc: linux-wireless <linux-wireless@vger.kernel.org>,
	Johannes Berg <johannes@sipsolutions.net>,
	make-wifi-fast@lists.bufferbloat.net,
	"codel@lists.bufferbloat.net" <codel@lists.bufferbloat.net>,
	Avery Pennarun <apenwarr@gmail.com>
Subject: Re: [PATCHv4 5/5] mac80211: add debug knobs for codel
Date: Thu, 5 May 2016 22:51:16 -0700	[thread overview]
Message-ID: <CAA93jw6dJ=fUK_Sr1Pcrm8wES9o_aC+oHqXcQksc_yKbqv8ikA@mail.gmail.com> (raw)
In-Reply-To: <CA+BoTQnED8EiLFNWq=8CPVAtufi0R5WjzAf6Pkf6cxUON_xY4g@mail.gmail.com>

On Thu, May 5, 2016 at 10:27 PM, Michal Kazior <michal.kazior@tieto.com> wrote:
> On 5 May 2016 at 17:21, Dave Taht <dave.taht@gmail.com> wrote:
>> On Thu, May 5, 2016 at 4:00 AM, Michal Kazior <michal.kazior@tieto.com> wrote:
>>> This adds a few debugfs entries to make it easier
>>> to test, debug and experiment.
>>
>> I might argue in favor of moving all these (inc the fq ones) into
>> their own dir, maybe "aqm" or "sqm".
>>
>> The mixture of read only stats and configuration vars is a bit confusing.
>>
>> Also in my testing of the previous patch, actually seeing the stats
>> get updated seemed to be highly async or inaccurate. For example, it
>> was obvious from the captures themselves that codel_ce_mark-ing was
>> happening, but the actual numbers out of wack with the mark seen or
>> fq_backlog seen.  (I can go back to revisit this)
>
> That's kind of expected since all of these bits are exposed as
> separate debugfs entries/files. To avoid that it'd be necessary to
> provide a single debugfs entry/file whose contents are generated on
> open() while holding local->fq.lock. But then you could argue it
> should contain all per-sta-tid info as well (backlog, flows, drops) as
> well instead of having them in netdev*/stations/*/txqs.
> Hmm..

I have not had time to write up todays results to any full extent, but
they were pretty spectacular.

I have a comparison of the baseline ath10k driver vs your 3.5 patchset
here on the second plot:

http://blog.cerowrt.org/post/predictive_codeling/

The raw data is here:
https://github.com/dtaht/blog-cerowrt/tree/master/content/flent/qca-10.2-fqmac35-codel-5

...

a note: quantum of the mtu (typically 1514) is a saner default than 300,

(the older patch I had, set it to 300, dunno what your default is now).

and quantum 1514, codel target 5ms rather than 20ms for this test
series was *just fine* (but more testing of the lower target is
needed)

However:

quantum "300" only makes sense for very, very low bandwidths (say <
6mbits), in other scenarios it just eats extra cpu (5 passes through
the loop to send a big packet) and disables
the "new/old" queue feature which helps "push" new flows to flow
balance. I'd default it to the larger value.

...

In other news, spacex just landed on the barge a few minutes ago.

The webcast is still going on
https://www.youtube.com/watch?v=L0bMeDj76ig and you can reverse it to
the landing.
:awesome:

>
>
> Michał

-- 
Dave Täht
Let's go make home routers and wifi faster! With better software!
http://blog.cerowrt.org