[Bridge] Packet loss / performance

dan-linuxbridge at unpossible.com dan-linuxbridge at unpossible.com
Thu Jan 13 13:55:37 PST 2005


I am attempting to build a bridge capable of functioning as near to gigabit
speeds as possible, with as many hundreds of thousands of packets per second
capabilities as possible.

My bridge system is a dual Opteron 246 (2.0Ghz); Tyan 2882 motherboard; 2 GB
PC3200 memory (1 GB in each CPU's bank; 128bit configuration); dual e1000
based NIC; 2.6.9 Kernel; NAPI enabled in the kernel and the NIC drivers; CPU
affinity ties each eth to a specific CPU; system otherwise idle.

Two test systems are connected, one to each interface in the Opteron.  Each
has a custom kernel with the Linux packet generator pktgen compiled as a
module.  Each test system can generate approximately 300,000 packets per

Before testing the bridge, I tested each eth interface separately.  I
brought up one interface on the Opteron, configured pktgen on the test
machine attached to that interface (set the IP address and destination mac
address) and sent the packets.  Using /proc/net/dev I could see the packets
being received at the Opteron and zero errors.  I repeated this test on the
other interface with the same results.  Results the same regardless of
number of packets sent.  It was able to handle the 300,000pps without issue.

Next I brought up the bridge.  I reconfigured pktgen on one test machine to
send packets to the IP and MAC address on the other test machine (across the
bridge).  When I run pktgen I have about 20% packet loss.

I sent 100,000 packets;
eth4 received ~80,000 packets; dropper/errs of ~70,000; ~20,000 fifo
eth3 sent ~77,000 packets

Somewhere I lost 20,000 packets at the receiving interface and another three
thousand before transmitting to the other side of the bridge.

I built this system based on specs that should do better.  If this were
running netfilter then I'd expect a capacity of around 700Kpps.  What's
happening is fairly opaque to me, so I'm not sure what to tune or where to
look.  Any assistance will be greatly appreciated.

Best regards,


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