Hi all,
Last week we have upgraded our infrastrucutre from ESX 3.5 -> latest 4.1u1 build 348481
Everything goes perfect except 6 vm servers.
This servers are installed with WS 2003 Ent R2 x86.
There is Installed TAME application (dos) on it
We used them for one very old but very business critical application and can't migrate it.
The database is CLIPPER.
We have used them perfectly on ESX3.5 without any issues.
After the migration to 4.1 this servers start bringing CPU performance issues.
Operations on server that takes approximatly 30 minutres, right now it takes more than 8 hours !!!!
We installed the new VMware tools - the result is the same.
We've uninstalled the new VMware tools - same
we've Vmotion it to different hosts - same
We;ve take snapshot on one of the vm servers, upgrade the VM to ver 7 (the old version of the VM is 4) - the result is - poor performance
no errors - just poor performance.
We was forced to reinstall one of the hosts again to 3.5
We've Vmotion the machine with the new VMware tools installed on it and revert it back to v4 - everything goes in place - working perfectly.
If someone have ideas why this thing happen ... please share it 
Thanks
Hm... I think that the problem is solved.
It was caused by the CPU instructions.
I've remove the AUTOMATIC CPU/MMU Virtualization and put it manuall on Use Intel VT-x/AMD-V for instruction set virtualization and Intel EPT/AMD RVI for MMU virtualization and the performance was back to normal
If someone have this pra-historic clipper databases and suffer like me - i think this will be helpfull