dummynet dropping too many packets

[rihad]

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?


$ 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 
-     -