Re: [LARTC] HTB MPU

[Andy Furniss <andy.furniss@dsl.pipex.com>]

Ed Wildgoose wrote:
> Andy Furniss wrote:
> 
>> Hi.
>>
>> I wrote in a reply to a mail on here recently that you can't set mpu 
>> (minimum packet unit) on HTB as you can on CBQ.
>>
>> I've just noticed that there is a patch on devik's site which does mpu 
>> and overhead.
>>
>> http://luxik.cdi.cz/~devik/qos/htb/
>>
>> For dsl users mpu is, for practical purposes going to be 106 - 
>> overhead is still variable though, depending on packet size.
>>
>> Having these should let you push upstream bandwidth rates a bit closer 
>> to the limit.
> 
> 
> 
> What about changing that patch a little (bear in mind I don't understand 
> how it works though).
> I appears that you could change the patch in tc/core in fn 
> tc_calc_rtable, from:
> 
>  + if (overhead)
>  +     sz += overhead;
> 
> to something like:
> 
>  + if (overhead)
>  +     sz += (((sz-1)/mpu)+1) * overhead;
> 
> Where that little calculation is trying to turn the mpu into a packet 
> size, work out how many packets would be required for the size (sz) of 
> data, and apply the overhead per packet.  You would then set mpu to be 
> the atm packet size, ie 54
> 
> To be honest though, this packing of the params into a single var seems 
> unneccessary.  The function  tc_calc_rtab is only obviously used in the 
> tc code, and it could be easily changed to have a prototype with an 
> extra param.  I would have to have a flick through the rest of the code, 
> but it might be quite easy to add per packet overhead to the cbq code in 
> the same way, and also whatever m_police is?
> 
> Can someone with a working setup try this out and see if it helps?

The patch author has mailed with similar suggestion, so there may be 
something new soon. People will need to work out their ppp overhead 
first. I know mine for pppoa/vc mux in the UK - it's 10 (the RFC says 9 
or 10) so it's lucky my modem gives a cell count so I can tell easily.
I don't know how many there are, or what figure other variants use.

Andy.


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