Thanks for quick response,

I've tried 'pti=off spectre_v2=off l1tf=off nospec_store_bypass_disable no_stf_barrier' (Xen/Dom0/guest) but no improvements.

I'm still curious enough to investigate further

Hello everyone,

could someone point me to a possible cause - and hopefully possible workarounds - in order to be able to use Xeon E7450 cores - even if only for sandbox/testing purposes.

The VM's were running perfectly on 6.5, but after upgrade to 7.6 performance dropped significantly - to the point of unusability. The same VMs - when using PV - still run perfectly. Moreover, windows machines (HVM) show no change of performance. Dom0 - also seems unaffected.
Cpu usage on those Linux HVM guests easily gets very high (100% all cores) - when given simple tasks, but I am unable to tell why.

I've tried messing with guest I/O schedulers, and disabling ucode loader in Xen, but nothing helped. I've also tried different network hardware.

I am aware that 'dunnington' cores are now unsupported (as of 8.1), but the problem exist also on 7.6.

I've tested on both (up to date) Centos 6 and Centos 7.

Thanks in advance,