Re: [LARTC] HTB rate miscalculation

["Marcus Felipe Pereira" <marcus@task.com.br>]

>> Hi,
>>  I've migrated my tc configuration from CBQ to HTB.
>>
>>  One problem appeared. Htb seems to miscalculate the bandwidth for 
>> classes with greater rates.
>>  For rates below 2Mbit there is almost no difference between the 
>> configured and the measured rate.
>>
>>  For large ones the problem starts. My root class has 10Mbit rate and 
>> when the interface has heavy trafic the measured bandwidth coudn't get 
>> more then 8.5Mbit.
>>
>>   "# tc -s class show ...." shows that the root class has about the 
>> 10Mbit, but the link stats shows mutch less.
>>
>>  The solution was to put the htb ceil on about 12Mbit. Then I can get to 
>> the 10Mbit. When using CBQ I didn't have this problem.
>>
>>  Is there any parameter that I can change to correct the rate 
>> calculation?
>>  Any one has similar problem?
>
> What counters are you using to measure?
>
> Does it do the same if you test with a single tcp stream and a very simple 
> setup like -
>
> tc qdisc add dev eth0 root handle 1:0 htb
> tc class add dev eth0 parent 1:0 classid 1:1 htb rate 10mbit
> tc filter add dev eth0 parent 1:0 protocol ip u32 match u32 0 0 flowid 1:1
>
> Andy.

I've done more tests, in fact there is a difference in the measure.

The rate measured by htb class, iptraf and iptables show very similar 
numbers.
The rate measured using SNMP ifInOctets and ifOutOctets (snmpget, ddrtool 
and mrtg) show rates about 20% less than htb.

Why this difference?

Marcus


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