running out of mbufs?

Brooks Davis brooks at one-eyed-alien.net
Wed Aug 3 04:44:01 GMT 2005


On Wed, Aug 03, 2005 at 01:49:32PM +1000, Dave+Seddon wrote:
> Greetings, 
> 
> I'm trying to do some performance testing of a content filtering system, so 
> I'm trying to get very high HTTP throughput.  I've got 4 * HP DL380s with 
> 3.4G Xeon processors (hyper threading) and 1 G RAM, 2 onboard BGEs, and 2 * 
> 2 port EM.  Using FreeBSD5.4-stable (as of 2005/08/02) and device polling, 
> I've configured a large number (246) VLAN interfaces on two machines, and 
> have apache on one box and siege on the other.  Using 'siege -f 
> /home/my_big_list_of_urls -c 50 --internet' one host does a large number of 
> request from the other machine.  I've been trying to tune for maximum 
> performance and have been using lots of examples for /etc/sysctl.conf and 
> so on from the web.  Adjusting these settings and running the siege, I've 
> found the apache server completely loses network connectivity when device 
> polling is enabled.  I've adjusted the HZ lots and found the system 
> survives the longest set a 15000 (yes it seems very large doesn't it).  The 
> problem now seems to be that I'm running out of mbufs: 

I doubt this is relevant, but it's worth noting that the vlan code is is
rather stupid in the face of large number of vlans because they are all
hung off a last.  Thus assuming even load, you're traversing an average
of 123 elements in the list per packet.  This might have a significant
impact on performance that could be causing excessive queuing.  It's
fairly easy to fix by allocating an array indexed by vlan so dispatch is
constant time (modulo cache effects), but it hasn't been done yet.

-- Brooks

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