Lost of performance over AMD-V with KVM?

[Victor fernandez <Victormanuel.fernandez@usc.es>]

Hi EveryBody!

recently, we have tested some specific High Energy Physics benchmarks that
was running over S.L.6 and we observed that the performance over AMD
machines was really bad, about 30-40% lost. We were investigating
and we conclude that the problem was with some cpu flags. These cpu
flags are important for running our application because it is optimazed
for running with them. So, we tuning our KVM with the name of flags
parameters and with "-cpu host" parameter too, but
we observed that the flags that we needed, they weren't included when
we started the S.L.6 instance. We try to solve it, but when we conclude
that the specific flags weren't included in the code of the last 
versions of KVM
and LibVirt(capabilities). Do you know something about this problem or
you are aware of this?

Thanks in advance,
     Víctor Fdez.