(no subject)

[Steffen Persvold]

Dear list people,

Lately I've been testing out a couple of Dell PowerEdge 2650 machines. 
These babies have dual onboard BCM95701A10 NICs (Tigon3 chip) mounted 
in the same PCI-X 133MHz 64 bit bus.

Since they have dual onboard GbE, I've been trying to channel bond them 
using just two crossover cables between two machines. The results I'm 
seeing is at the first glance very strange. What I see is that the 
performance when bonded (round robin) is about _half_ (and sometimes even 
less) compared to just using a single interface. Here are some netpipe-2.4 
results :

64k message size, single interface
  1:     65536 bytes  190 times -->  760.54 Mbps in 0.000657 sec

256k message size, single interface
  1:    262144 bytes   53 times -->  855.04 Mbps in 0.002339 sec

64 message size, both interfaces (using round robin)
  1:     65536 bytes   65 times -->  257.06 Mbps in 0.001945 sec

256k message size, both interfaces (using round robin)
  1:    262144 bytes   25 times -->  376.01 Mbps in 0.005319 sec

Looking at the output of netstat -s after a testrun with 256k message 
size, I see some differences (main items) :

Single interface :
 Tcp:
      0 segments retransmited

 TcpExt:
     109616 packets directly queued to recvmsg prequeue.
     52249581 packets directly received from backlog
     125694404 packets directly received from prequeue
     78 packets header predicted
     124999 packets header predicted and directly queued to user
     TCPPureAcks: 93
     TCPHPAcks: 22981

      
Bonded interfaces :
  Tcp:
      234 segments retransmited

  TcpExt:
      1 delayed acks sent
      Quick ack mode was activated 234 times
      67087 packets directly queued to recvmsg prequeue.
      6058227 packets directly received from backlog
      13276665 packets directly received from prequeue
      6232 packets header predicted
      4625 packets header predicted and directly queued to user
      TCPPureAcks: 25708
      TCPHPAcks: 4456

The biggest difference as far as I can see is the 'packtes header 
predicted', 'packets header predicted and directly queued to user', 
'TCPPureAcks' and TCPHPAcks.

I have an idea that this happens because the packets are comming out of 
order into the receiving node (i.e the bonding device is alternating 
between each interface when sending, and when the receiving node gets the 
packets it is possible that the first interface get packets number 0, 2, 
4 and 6 in one interrupt and queues it to the network stack before packet 
1, 3, 5 is handled on the other interface).

If this is the case, any ideas how to fix this...

I would really love to get 2Gbit/sec on these machines....

PS

I've also seen this feature on the Intel GbE cards (e1000), but these 
drivers has a parameter named RxIntDelay which can be set to 0 to get 
interrupt for each packet. Is this possible with the tg3 driver too ?

DS

Regards,
--
  Steffen Persvold   |       Scali AS
 mailto:[e-mail] |  http://www.scali.com
Tel: [phone] |   Olaf Helsets vei 6
Fax: [phone] |   N0621 Oslo, NORWAY