Lag server at the begining of a Round

[DoOm]

i've made nothing on the server, just steam update , i've no re-format
At the end of a round my server has 450 FPS , but at the begining the falling to 10 !!!

but a host who had run 3 servers in the same time , who's going to lag after a update...
i don't think it was an hardware problem

i'm wonder of the hyperthreading on the processors , i've heard that a update of steam could make pb.