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

Rich Brown richb.hanover at gmail.com
Tue Feb 25 08:09:53 EST 2014

Thanks everyone for all the good advice. I will summarize my responses to all your notes now, then I'll go away and run more tests.

- Yes, I am using netperf 2.6.0 and netperf-wrapper from Toke's github repo.

- The "sync rate" is the speed with which the DSL modem sends bits to/from my house. I got this by going into the modem's admin interface and poking around. (It turns out that I have a very clean line, high SNR, low attenuation. I'm much less than a km from the central office.) So actual speed should approach this, except...

- Of course, I have to subtract all those overheads that Sebastian described - ATM 48-in-53, which knocks off 10%; ATM frame overhead which could add up to 47 bytes padding to any packet, etc.)

- I looked at the target calculation in Dave's Home Gateway best practices. (http://snapon.lab.bufferbloat.net/~d/draft-taht-home-gateway-best-practices-00.html) Am I correct that it sets the target to five 1500-byte packet transmission time or 5 msec, whichever is greater?

- I was astonished by the calculation of the bandwidth consumed by acks in the reverse direction. In a 7mbps/768kbps setting, I'm going to lose one quarter of the reverse bandwidth? Wow!

- I wasn't entirely clear how to set the target in the SQM GUI. I believe that "target ##msec" is an acceptable format. Is that correct?

- There's also a discussion of setting the target with "auto", but I'm not sure I understand the syntax.

Now to find some time to go back into the measurement lab! I'll report again when I have more data. Thanks again.


On Feb 24, 2014, at 9:56 AM, Aaron Wood <woody77 at gmail.com> wrote:

> Do you have the latest (head) version of netperf and netperf-wrapper?  some changes were made to both that give better UDP results.
> -Aaron
> On Mon, Feb 24, 2014 at 3:36 PM, 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.
> - 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.
> 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...
> 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
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