dummynet dropping too many packets
rihad at mail.ru
Tue Oct 6 09:34:37 UTC 2009
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.
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