I have noticed a significant decrease in performance on NFS in 
2.6.0-test7 and later. I have tested kernels 2.4.22-xfs and 
2.6.0-test[4-10], kernels 2.6.0-test[4-6] all gave the same high 
performance and kernels 2.6.0-test[7-10] all gave the same low 
performance. I have saved testresults with kernels 2.4.22-xfs, 
2.6.0-test6, 2.6.0-test7 and 2.6.0-test10.

The time it takes to copy a 100 million byte file from my file server 
(which runs on RedHat 9 with a 2.4.19-xfs kernel) is 3 to 4 times longer 
while running 2.6.0-test[7-10] than 2.6.0-test[4-6].

I have tested this by creating a 100 million byte file on the fileserver 
with dd:
dd if=/dev/zero of=100000000.bytes bs=1000000 count=100

Then I have timed the time it takes to cat the file to /dev/null on my 
workstation:
/usr/bin/time cat /mnt/home/fredrik/100000000.bytes > /dev/null

I have also run netstat -s and nfsstat right after the above command and 
put the output in a file test.txt, attached to this mail.

I have verified that the problem isn't with the network card by using 
netcat (nc) to transfer to file.

The relevant line in my fstab is:
maggie:/home            /mnt/home               nfs     defaults        0 0

I have tried different rsize and wsize options to mount with no success.

The output for the test.txt file is generated by a small script that runs:
uname -r
/usr/bin/time cat /mnt/home/fredrik/100000000.bytes > /dev/null
netstat -s
nfsstat

The tests for all kernels are on a freshly booted kernel.

mount --version gives:
mount: mount-2.11y

The only thing that stands out to me (not a kernel hacker) is that for 
2.6.0-test[7,10] and 2.4.22-xfs netstat -s reports a large number of 
packets that it failed to reassemble, while 2.6.0-test6 reports none. 
Also 2.6.0-test[7,10] and 2.4.22-xfs nfsstat reports a large number of 
resends while 2.6.0-test6 reports no resends. Although 2.4.22-xfs and 
2.6.0-test[7,10] both reports about the same number of resends and 
failed reassembled packets, 2.4.22-xfs is more then twice as fast to 
transfer the file than 2.6.0-test[7,10].

Anyone can give a good explanation?
If you need more details and/or other information, feel free to ask.