Why is my gigabit ethernet so slow?

[Martti Kuparinen <martti.kuparinen%iki.fi@localhost>]

Hi,

My test router has


NetBSD 5.99.24 (GENERIC) #0: Tue Jan 26 11:29:49 EET 2010
        root%xxxx.com@localhost:/usr/src/sys/arch/amd64/compile/GENERIC
total memory = 2045 MB
avail memory = 1966 MB
timecounter: Timecounters tick every 10.000 msec
timecounter: Timecounter "i8254" frequency 1193182 Hz quality 100
Dell Inc.                 Precision WorkStation 390
mainbus0 (root)
cpu0 at mainbus0 apid 0: Intel 686-class, 2660MHz, id 0x6f6
cpu1 at mainbus0 apid 1: Intel 686-class, 2660MHz, id 0x6f6
...
wm0 at pci7 dev 0 function 0: Intel PRO/1000 QT (82571EB), rev. 6
wm0: interrupting at ioapic0 pin 16
wm0: PCI-Express bus
wm0: 65536 word (16 address bits) SPI EEPROM
wm0: Ethernet address 00:15:17:c6:69:c0
igphy0 at wm0 phy 1: Intel IGP01E1000 Gigabit PHY, rev. 0
igphy0: 10baseT, 10baseT-FDX, 100baseTX, 100baseTX-FDX, 1000baseT, 
1000baseT-FDX, auto


I connected my Ubuntu laptop with a direct cable and ran TTCP. I only got

ttcp-t: 1073741824 bytes in 26.04 real seconds = 314.56 Mbit/sec +++
ttcp-t: 131072 I/O calls, msec/call = 0.20, calls/sec = 5033.02
ttcp-t: 0.0user 2.3sys 0:26real 9% 0i+0d 0maxrss 0+2pf 16760+0csw

Next I tried my laptop against another PC with Ubuntu 9.10 (with an identical 
quad-port Intel card but with more memory and slightly faster quad-core CPU) and 
I got

ttcp-t: 1073741824 bytes in 9.16 real seconds = 894.58 Mbit/sec +++
ttcp-t: 131072 I/O calls, msec/call = 0.07, calls/sec = 14313.29
ttcp-t: 0.0user 2.0sys 0:09real 23% 0i+0d 0maxrss 0+2pf 1675+0csw

In both cases MTU was 1500, in fact using MTU 9000 made things worse with the 
NetBSD router and the speed drop to 40-50 Mbps. Hardware checksumming (IPv4) had 
no real effect on the speed.

How can I get better speed (800+ Mbps) within NetBSD?

Martti