Virtio disk driver performance on NetBSD

Bonnie ++ on NetBSD/kvm:
with virtio:
/home/manu $ dmesg | grep virtio1
virtio1 at pci0 dev 4 function 0
virtio1: Virtio Block Device (rev. 0x00)
ld0 at virtio1
virtio1: allocated 45056 byte for virtqueue 0 for I/O request, size 128
virtio1: using 36864 byte (2304 entries) indirect descriptors
virtio1: interrupting at ioapic0 pin 11

Version 1.03e       ------Sequential Output------ --Sequential Input- --Random-
                    -Per Chr- --Block-- -Rewrite- -Per Chr- --Block-- --Seeks--
Machine        Size K/sec %CP K/sec %CP K/sec %CP K/sec %CP K/sec %CP  /sec %CP
netbook.libera 300M 27841  27 25160  26 22670  27 109146  89 250943  99 +++++ +++
                    ------Sequential Create------ --------Random Create--------
                    -Create-- --Read--- -Delete-- -Create-- --Read--- -Delete--
              files  /sec %CP  /sec %CP  /sec %CP  /sec %CP  /sec %CP  /sec %CP
                 16   282  42 +++++ +++   966  17   310  38  2736  99   603  40
netbook.libera.cc,300M,27841,27,25160,26,22670,27,109146,89,250943,99,+++++,+++,16,282,42,+++++,+++,966,17,310,38,2736,99,603,40

scp /home/manu/Projects/emul/i386/installers/NetBSD-6.0_BETA_i386_boot-com.iso manu@192.168.178.31:
Password:
NetBSD-6.0_BETA_i386_boot-com.iso             100%   44MB   4.0MB/s   00:11

without virtio:
dmesg | grep atabus0
atabus0 at piixide0 channel 0
wd0 at atabus0 drive 0
Version 1.03e       ------Sequential Output------ --Sequential Input- --Random-
                    -Per Chr- --Block-- -Rewrite- -Per Chr- --Block-- --Seeks--
Machine        Size K/sec %CP K/sec %CP K/sec %CP K/sec %CP K/sec %CP  /sec %CP
netbook.libera 300M  7059  30  7771  30  6514  30 128430 100 252140 101 14682  88
                    ------Sequential Create------ --------Random Create--------
                    -Create-- --Read--- -Delete-- -Create-- --Read--- -Delete--
              files  /sec %CP  /sec %CP  /sec %CP  /sec %CP  /sec %CP  /sec %CP
                 16   168  72 +++++ +++   432  54   173  72  2788 100   379  66
netbook.libera.cc,300M,7059,30,7771,30,6514,30,128430,100,252140,101,14682.4,88,16,168,72,+++++,+++,432,54,173,72,2788,100,379,66