Bug 762314 (GLUSTER-582)

The bug can be replicated by running postmark benchmark configured for the 
metadata operations - around 1kb files in high numbers

Use a standard server side vol-spec file with io-threads 8.
and client side:

# file: /etc/glusterfs/glusterfs-client.vol
volume s1
  type protocol/client
  option transport-type ib-verbs
  option remote-host 10.24.2.128 
  option remote-subvolume brick
end-volume

volume s2
  type protocol/client
  option transport-type ib-verbs
  option remote-host 10.24.2.129 
  option remote-subvolume brick
end-volume

volume dstr
  type cluster/distribute
  subvolumes s1 s2 
end-volume

volume writebehind
  type performance/write-behind
  option window-size 2KB
  option flush-behind on
  subvolumes dstr
end-volume

----------------------------
then run postmark with following pmrc file

set size 1024 1048
set number 25000
set location /gmnt/n142   ## Location of glusterfs mounted directory
set read 8192
set write 8192
set report verbose
run /root/pmr142
quit

---------------------------------

If this is hit on 2 servers with 4 clients running postmark you would 
see performance of ~700 creates/sec.
(or 1 server with 2 clients)

But if the number is reduced to 12500 the performance you get is ~1400 creates/sec.

The performance should not critically depend upon number of files being created.
We tried to analyze the cause and found this was a server-side artifact.
If we saw "top" on the servers while postmark was being run with 50000 files
we saw very high CPU utilization. The CPU utilization went down to negligible 
for half the number of files - this shows up in the performance.