[Cerowrt-devel] Equivocal results with using 3.10.28-14

[Dave Taht]

On Mon, Feb 24, 2014 at 10:51 AM, Dave Taht <dave.taht at gmail.com> wrote:
> On Mon, Feb 24, 2014 at 9:36 AM, Rich Brown <richb.hanover at gmail.com> wrote:
>>
>> CeroWrt 3.10.28-14 is doing a good job of keeping latency low. But... it has two other effects:
>>
>> - I don't get the full "7 mbps down, 768 kbps up" as touted by my DSL provider (Fairpoint). In fact, CeroWrt struggles to get above 6.0/0.6 mbps.
>
> 0) try the tcp_upload or tcp_download or tcp_bidir tests to get
> results closer to what your provider claims.
>
> since your plots are pretty sane, you can get cleaner ones with using
> the 'totals' plot type
> and/or comparing multiple runs to get a cdf
>
> -p totals or -p icmp (theres a few different ones, --list-plots
>
> -i somerun.json.gz -i somerun2.json.gz
>
>
> 1) http://richb-hanover.com/wp-content/uploads/2014/02/6854-777-dflt-sqm-disabled1.png
>
> is your baseline without SQM?
>
> If so why do you compare the providers stated rate...
>
>    with the measured rate with/without SQM?
>
> These are two measures of the truth - one with and without a change.
>
> Vs a providers claim for link rate that doesn't account for real
> packet dynamics.

I awoke mildly grumpy this morning, sorry. The the sqm-disabled link
above shows you
getting less than a mbit down under the providers default settings.

So rather than saying you lose 10% of link bandwidth relative to the
stated ISP specification,
I prefer to think you are getting 6x more usable bandwidth from using
SQM, and somewhere
around 1/25th or more less latency.

Making tcp's congestion avoidance work rapidly and avoiding bursty
packet loss leads to
more usable bandwidth.

> 2) the netperf reporting interval is too high to get good measurements
> at below a few
> mbit, so you kind of have to give up on the upload chart at these
> rates. (totals chart is
> clearer)
>
> Note that the tcp acks are invisible - you are getting >6mbit down,
> and sending back approximately
> 150kbit in acks which we can't easily measure. The overhead in the
> measurement streams is
> relative to the RTT as well.
>
> I'd really like to get to a test that emulated tcp and got a fully
> correct measurement.
>
> 3) Generally using a larger fq_codel target will give you better
> upload throughput and
> better utiliziation at these rates. try target 40ms as a start. We've
> embedded a version
> of the calculation in the latest cero build attempts (but other stuff is broke)
>
> nfq_codel seems also do to give a better balance between up and
> downloads at low rates,
> also with a larger target.
>
> it looks like overhead 44 is about right and your first set of charts
> about right.

so if you could repeat your first set of tests changing the target to at least
40ms on the upload, and trying both nfq_codel and fq_codel, you'll be getting
somewhere.

nfq_codel behaves more like SFQ, and is probably closer to what more people
want at these speeds.

>
>
>
>>
>> - When I adjust the SQM parameters to get close to those numbers, I get increasing levels of packet loss (5-8%) during a concurrent ping test.
>
> Shows the pings are now accruing delay.
>
>>
>> So my question to the group is whether this behavior makes sense: that we can have low latency while losing ~10% of the link capacity, or that getting close to the link capacity should induce large packet loss...
>
> You never had the 10% in the first place.
>
>>
>> Experimental setup:
>>
>> I'm using a Comtrend 583-U DSL modem, that has a sync rate of 7616 kbps down, 864 kbps up. Theoretically, I should be able to tell SQM to use numbers a bit lower than those values, with an ATM plus header overhead with default settings.
>>
>> I have posted the results of my netperf-wrapper trials at http://richb-hanover.com - There are a number of RRUL charts, taken with different link rates configured, and with different link layers.
>>
>> I welcome people's thoughts for other tests/adjustments/etc.
>>
>> Rich Brown
>> Hanover, NH USA
>>
>> PS I did try the 3.10.28-16, but ran into troubles with wifi and ethernet connectivity. I must have screwed up my local configuration - I was doing it quickly - so I rolled back to 3.10.28.14.
>
>
> manually adjust the target.
>
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>
>
>
> --
> Dave Täht
>
> Fixing bufferbloat with cerowrt: http://www.teklibre.com/cerowrt/subscribe.html



-- 
Dave Täht

Fixing bufferbloat with cerowrt: http://www.teklibre.com/cerowrt/subscribe.html