[CentOS] Performance problems with XFS on Centos 5.4

Hi!

During the last weeks I experienced some performance problems with a
large file-system on XFS basis. Sometimes for instance ls is
painfully. Immidiatly afterwards ls on the same directory is
immidiate. I used strace on this ls and found that during the first ls
the lstat-calls need approx 0.02s each while during the second ls the
are two orders of magnitude faster.

Googling around I stumbled upon some messages similar like this

http://www.opensubscriber.com/message/linux-xfs@oss.sgi.com/1355060.html

which have in common
a) they're from around 2006
b) they suggest to increase a mount-option ihashsize. This mount
   option is listed as deprecated in the current kernel-doc

So my question: does anyone have experience with that kind of
performance problem? Do you think it is a XFS problem or are there
some other tuning parameters in the kernel that could be modified for
instance via /proc?

The reason why I'm asking here is that it is a production file-system
so I would be very unpopular if I experiment too much (a couple of
reboots is OK ;) )

Bernhard

PS: the situation got worse during the last weeks when the file-system
increased in size, so the option that some kind of buffer now is too
small and I'm experiencing some kind of thrashing seems very likely to
me