dummynet dropping too many packets

[Julian Elischer]

rihad wrote:
> Luigi Rizzo wrote:
>> On Mon, Oct 05, 2009 at 05:12:11PM +0500, rihad wrote:
>>> Luigi Rizzo wrote:
>>>> On Mon, Oct 05, 2009 at 04:29:02PM +0500, rihad wrote:
>>>>> Luigi Rizzo wrote:
>>>> ...
>>>>>> you keep omitting the important info i.e. whether individual
>>>>>> pipes have drops, significant queue lenghts and so on.
>>>>>>
>>>>> Sorry. Almost everyone has 0 in the last Drp column, but some have 
>>>>> above zero. I'm not just sure how this can be helpful to anyone.
>>>> because you were complaining about 'dummynet causing drops and
>>>> waste of bandwidth'.
>>>> Now, drops could be due to either
>>>> 1) some saturation in the dummynet machine (memory shortage, cpu
>>>>   shortage, etc.) which cause unwanted drops;
>>>>
>>> I too think the box is hitting some other global limit and dropping 
>>> packets. If not, then how come that between 4a.m. and 10a.m. when the 
>>> traffic load is at 250-330 mbit/s there isn't a single drop?
>>
>> there may be different reasons, e.g. the big offenders were
>> idle when you saw no drops. You still do not have enough
>> information on which packets are dropped and where,
>> so you cannot prove your assumptions.
>>
>> Also, below:
>> 1. increasing the queue size won't help at all. Those
>>    who overflow a queue of 1000 slots will also overflow
>>    a queue of 10k slots.
>>
> 
>> 2. your test with 'ipfw allow ip from any to any' does not
>>    prove that the interface queue is not saturating, because
>>    you also remove the burstiness that dummynet introduces,
>>    and so the queue is driven differently.
>>
> 
> There's one thing I noticed:
> net.inet.ip.dummynet.io_pkt_drop doesn't grow! But still around 400 
> packets dropped per second.
> net.inet.ip.dummynet.tick_lost is always zero
> net.inet.ip.dummynet.tick_diff: grows at about 50 per second.
> net.inet.ip.dummynet.tick_adjustment: grows at about 5 per second.
> 
> How do I investigate and fix this burstiness issue?

higher Hz rate?

> 
> 
> $ netstat -i
> Name    Mtu Network       Address              Ipkts Ierrs    Opkts 
> Oerrs  Coll
> bce0   1500 <Link#1>      00:1d:09:xx:xx:xx 24777049059     0 75426020 
>    0     0
> bce0   1500 xx.xx.xx.xx/xx my.hostname       159293969     - 75282225   
> -     -
> bce1   1500 <Link#2>      00:1d:09:xx:xx:xx   724725     0 24514919344 
>    0     0
> bce1   1500 192.168.94.0  local.hostname      656243     - 83024869 -     -
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