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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:sp@scali.com | http://www.scali.com
Tel: (+47) 2262 8950 | Olaf Helsets vei 6
Fax: (+47) 2262 8951 | N0621 Oslo, NORWAY


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