dummynet dropping too many packets

[rihad]

Luigi Rizzo wrote:
> On Tue, Oct 06, 2009 at 02:21:38PM +0500, rihad wrote:
>> rihad wrote:
>>> Julian Elischer wrote:
>>>> rihad wrote:
>>>>> Luigi Rizzo wrote:
>>>>>> 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.
>>>>>>
>>>>> How do I investigate and fix this burstiness issue?
>>>> higher Hz rate?
>>>>
>>> Rebooted with HZ=2000 10 minutes ago. Due to application design the ipfw 
>>> table (pipe tablearg) was flushed, so there are now 350 (and increasing 
>>> at a rate 1 per 1-2 seconds as I type this) or so users in the table, 
>>> and not 4k as normally would be. The box is servicing 450+ mbit/s 
>>> without a single drop. I want to monitor how things change once the 
>>> number of users in ipfw tables gradually increases up to several thousands.
>>>
>> It starts dropping packets at around 2000 online users (ipfw table 
>> load). I've set up a shell script to monitor this:
> 
> once again:
> you should check which pipes are dropping packets and whether
> the number of drops indicated in the pipes matches the counts
> indicated by netstat.
> 
It's impossible to do so accurately, since users come and go any moment, 
and their pipes expire, and it's plain useless. As to the accordance of 
packet drop rate with net.inet.ip.dummynet.io_pkt_drop, they vary wildly:

8664 output packets dropped due to no bufs, etc.
net.inet.ip.dummynet.io_pkt_drop: 111

since boottime!