Re: [LARTC] HTB and PRIO qdiscs introducing extra latency when output

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

Andy Furniss wrote:
> Jonathan Lynch wrote:

>> If the ceil is based at IP level then the max ceil is going to be a
>> value between 54 Mbit and 97 Mbit (not the tc values) for a 100 Mbit
>> interface depending on the size of the packets passing through, right ?
>>
>> Minimum Ethernet frame
>> 148,809 * (46 * 8) =   148,809 * 368 = 54,761,712 Mbps
>>
>> Maximum Ethernet frame
>> 8,127 * (1500 * 8) =   8,127 * 12,000 =  97,524,000 Mbps
> 
> 
> If you use the overhead option I think you will be to overcome this 
> limitation and push the rates closer to 100mbit.

I looked up ethernet overheads and found the figure of 38 bytes per 
frame, the 46 is min eth payload size? and looking at the way mpu is 
handled by the tc rate table generator I think you would need to use 46 
+ 38 as mpu.

So on every htb line that has a rate put ..... overhead 38 mpu 84

I haven't checked those figures or tested close to limits though, the 
12k burst would need increasing a bit aswell or that will slightly over 
limit rate at HZ\x1000.

Andy.
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