Comment 18 for bug 1006446

All right,

I am doing tests right now, but as far as I can see the 3.4.0-030400-generic kernel has the same behaviour as stock ubuntu 12.04.

With ubuntu server and this 3.4 kernel:
Test:
- all workstation writing a separate 4GB file with `dd´ to /testhome, which is nfs4 mounted from an ubuntu server 12.04.
Result:
- all other processes started on the same machine, that want to read or write to the same mountpoint, after this dd began just block.
   for instance:
      ls just waits until dd is finished.
      commandline completion never finishes and the shell just blocks.
- load on the server goes beyond 90, and nfs kernel threads consume lots of cpu. There is also a lot of io waiting,
  which is to be expected.
- Also the nfs kernel threads are unevenly loaded it seems. There is a bunch (10-20) which use
about 20-30%, and it tapers off to 3-0.5%.

With RHEL6 server:
Test:
- same test, but to /data/misc, mounted nfs4 from redhat 6.3 server.
Result:
- processes started after dd began, wanting to read or write to the same mountpoint (/data/misc) block a few seconds but then start.
   for instance:
      ls waits for 5-6 seconds and then just answers.
     commandline completion waits about the same time and then completes the command or whatever it completes.
- load on the server is also over 90, but the nfs kernel threads consume not so much cpu. Lots of io waiting.
- nfs kernel threads are very evenly loaded. I see a long list of them using about 3% each. It goes up to maybe 5% and down
to about 2%, and some of the 128 available threads are unused. I think more than half of them are active during the test.

Keep in mind that this is a pretty heavy test (well I think it is anyway). But the ubuntu server already had big problems when the nfs usage is normal. Normal in our case means:
- some people editing a few text files
- a lot of people using web or mail, and therefore their firefox cache and the mail server accesses nfs-mounted /home/$USER/Maildir
- some people doing heavy calculations and writing either a lot of small files or a few big ones. Small means about 1MB, big means several GB.