virtio disk and network performances

Hello,
I am little bit disappointed about virtio perormance.

speaking about virtio disk performance I get about the same performances of non-virtio quests. I am using centos 5.3 2.6.18-128.1.6.el5 as host and the same centos 5.3 2.6.18-128.1.6.el5 as kvm guests with virtio backported to CentOS 5.2 kernel

virtio_net             47169  0
virtio_blk             41417  3
virtio_pci             41921  0
virtio_ring            37441  1 virtio_pci
virtio                 39365  3 virtio_net,virtio_blk,virtio_pci

Filesystem Size Used Avail Use% Mounted on
/dev/mapper/VolGroup00-LogVol00

                     9.1G  1.5G  7.2G  17% /

/dev/vda1 99M 19M 76M 20% /boot
tmpfs 502M 0 502M 0% /dev/shm

I use bonnie++ for I/O tests and I got closely the same results for virtio guests and non-virtio guests. Anyone experienced something different ?

Speaking about virtio net performance I get good results but they are not symmetric.

on a virtio guest I get ~1Gb/s inbound and ~600Mb/s outbound

without virtio I get ~600Gb/s inbound and ~200MB/s outbound

anyone has any idea how come hte performance is not symmetric ?

thanks

Rick