Re: [LARTC] patch: HTB update for ADSL users

[Jason Boxman <jasonb@edseek.com>]

On Tuesday 22 June 2004 06:00, Ed Wildgoose wrote:
> >I'm running PPPoEoATM here.  I don't know what my actual PPPoE overhead
> > is, but I guess 10 bytes is reasonably close enough.  PPPoE is handled by
> > my Westell Wirespeed, which doesn't provide any useful cell information. 
> > At the moment I cannot easily obtain a cell count to determine my actual
> > PPP overhead.
>
> Try bumping the protocol_overhead up to 16 for PPPoE (from 10).  You
> should also make sure that your MTU is lower than that required by your
> PPPoE provider or else you will get ethernet packet fragmentation and I
> doubt we want to extend the patch to cover those situations anyway.

The largest MTU I could use is 1492.  I have the Westell Wirespeed handling 
PPPoE, so I speak through eth0 locally.  Until recently that was fine, but 
now I need to use 1492 instead of 1500 on eth0 due to strange SSH hangs that 
haven't happened in a year at 1500 with the same configuration.  It's odd.  
All other machines are using 1500 without incident.

> The patch should actually have most benefit when you are doing transfers
> with smaller packets.  I think with larger constant streams like the one
> you tested, there will be little difference between bumping up the
> interface speed with the patch or leaving it all as it was (at the end
> of the day we are mostly just shifting the calculation of interface
> speed somewhere else).

Without the patch, if I set my rate to 256 * 0.8, I die.  The connection is 
not completely unusable, but gaming is extremely laggy and Web traffic is 
noticeably laggy, although pages still load with about 2s (versus a few 
hundred ms without the patch at 160kbit).  With the patch I can set it to 
224, so there's obviously a large improvement even with mostly large TCP 
packets going out doing a bulk `scp` copy.

> >Perhaps I need to idle everything and do one of those 'speed tests' to see
> >what my actual upstream is.  Could be it's really around 224, since I'm
> > not guaranteed 256 by my ISP anyway.
>
> Your upstream will be 256Kbits of ATM bandwidth.   This consists of 53
> byte packets with 48 bytes of data.  So you already only have 256 *
> 48/53 of real bandwidth.  We then have to take off PPP headers and PPPoE
> headers.

That's the maximum promised speed from my ISP.  In reality, of course, line 
conditions might result in my true speed not being that high, before 
accounting for overhead and things.

> We are obviously still a few bytes out with this patch or else you
> should be able to crank up the speed to 250 ish and still see your ping
> speeds stay low.  I will investigate further

Okay, if you're sure it's not just my line having a true upstream less than 
the consumer rated speed it was assigned. ;)

> Ed W
>

-- 

Jason Boxman
Perl Programmer / *NIX Systems Administrator
Shimberg Center for Affordable Housing | University of Florida
http://edseek.com/ - Linux and FOSS stuff

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