i have a KVM linux based virtual machines, as the network performance of the host is running perfect with 1GB/s(in internal network) and using iperf tools it show that the network is running perfect in host , but guests is slow network performance as iperf result was so strange as it is not 100MB/s and is not 1GB/s its range between 350 and 500MB/s maximum, and this is result of using iperf command (iperf -c servername -P 15)

[ ID] Interval       Transfer     Bandwidth
[ 17]  0.0-10.0 sec  68.6 MBytes  57.5 Mbits/sec
[ ID] Interval       Transfer     Bandwidth
[  4]  0.0-10.0 sec  18.6 MBytes  15.5 Mbits/sec
[ ID] Interval       Transfer     Bandwidth
[  5]  0.0-10.0 sec  61.9 MBytes  51.9 Mbits/sec
[ ID] Interval       Transfer     Bandwidth
[ 11]  0.0-10.0 sec  16.0 MBytes  13.4 Mbits/sec
[ ID] Interval       Transfer     Bandwidth
[ 10]  0.0-10.0 sec  24.3 MBytes  20.4 Mbits/sec
[ ID] Interval       Transfer     Bandwidth
[ 15]  0.0-10.0 sec  20.2 MBytes  16.9 Mbits/sec
[ ID] Interval       Transfer     Bandwidth
[ 12]  0.0-10.0 sec  30.2 MBytes  25.3 Mbits/sec
[ ID] Interval       Transfer     Bandwidth
[  3]  0.0-10.0 sec  36.2 MBytes  30.3 Mbits/sec
[ ID] Interval       Transfer     Bandwidth
[  8]  0.0-10.0 sec  23.6 MBytes  19.8 Mbits/sec
[ ID] Interval       Transfer     Bandwidth
[  9]  0.0-10.0 sec  24.2 MBytes  20.3 Mbits/sec
[ ID] Interval       Transfer     Bandwidth
[ 14]  0.0-10.0 sec  31.0 MBytes  25.9 Mbits/sec
[ ID] Interval       Transfer     Bandwidth
[  7]  0.0-10.0 sec  16.6 MBytes  13.9 Mbits/sec
[ ID] Interval       Transfer     Bandwidth
[  6]  0.0-10.0 sec  18.8 MBytes  15.7 Mbits/sec
[ ID] Interval       Transfer     Bandwidth
[ 13]  0.0-10.0 sec  13.3 MBytes  11.2 Mbits/sec
[ ID] Interval       Transfer     Bandwidth
[ 16]  0.0-10.0 sec  29.6 MBytes  24.8 Mbits/sec
[SUM]  0.0-10.0 sec    433 MBytes    363 Mbits/sec

i tested different network models and the best result was with the virtio model any one please can help to get the full performance of network and be 1 GB/s