FreeBSD 7, bridge, PF and syn flood = very bad performance

Stefan Lambrev stefan.lambrev at moneybookers.com
Sun Jan 27 06:29:21 PST 2008


Greetings,

Max Laier wrote:

-cut-
>> Well I think the interesting lines from this experiment are:
>> max              total            wait_total       count   avg
>> wait_avg     cnt_hold     cnt_lock name
>>     39            25328476     70950955     9015860     2     7
>> 5854948      6309848 /usr/src/sys/contrib/pf/net/pf.c:6729 (sleep
>> mutex:pf task mtx)
>> 936935        10645209          350          50 212904     7
>> 110           47 /usr/src/sys/contrib/pf/net/pf.c:980 (sleep mutex:pf
>> task mtx)
>>     
>
> Yeah, those two mostly are the culprit, but a quick fix is not really 
> available.  You can try to "set timeout interval" to something bigger 
> (e.g. 60 seconds) which will decrease the average hold time of the second 
> lock instance at the cost of increased peak memory usage.
>   
I'll try and this. At least memory doesn't seems to be a problem :)
> I have the ideas how to fix this, but it will take much much more time 
> than I currently have for FreeBSD :-\  In general this requires a bottom 
> up redesign of pf locking and some data structures involved in the state 
> tree handling.
>
> The first(=main) lock instance is also far from optimal (i.e. pf is a 
> congestion point in the bridge forwarding path).  For this I have also a 
> plan how to make at least state table lookups run in parallel to some 
> extend, but again the lack of free time to spend coding prevents me from 
> doing it at the moment :-\
>   
Well, now we know where the issue is. The same problem seems to affect 
synproxy state btw.
Can I expect better performance with IPFW's dynamic rules?
I wonder how one can protect himself on gigabit network and service more 
then 500pps.
For example in my test lab I see incoming ~400k packets per second, but 
if I activate PF,
I see only 130-140k packets per second. Is this expected behavior, if PF 
cannot handle so many packets?
The missing 250k+ are not listed as discarded or other errors, which is 
weird.

-- 

Best Wishes,
Stefan Lambrev
ICQ# 24134177



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