comparação de desempenho dos drivers e1000 e virtio-pci

Question

Eu fiz a seguinte configuração para comparar o desempenho dos drivers virtio-pci e e1000 :

Eu esperava ver uma taxa de transferência muito maior no caso de virtio-pci em comparação com e1000 , mas eles tiveram um desempenho idêntico.

Teste com virtio-pci ( 192.168.0.126 está configurado para T60 e 192.168.0.129 está configurado para PC1 ):

root@PC1:~# grep hype /proc/cpuinfo
flags       : fpu de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pse36 clflush mmx fxsr sse sse2 syscall nx lm rep_good nopl pni vmx cx16 x2apic hypervisor lahf_lm tpr_shadow vnmi flexpriority ept vpid
root@PC1:~# lspci -s 00:03.0 -v
00:03.0 Ethernet controller: Red Hat, Inc Virtio network device
    Subsystem: Red Hat, Inc Device 0001
    Physical Slot: 3
    Flags: bus master, fast devsel, latency 0, IRQ 11
    I/O ports at c000 [size=32]
    Memory at febd1000 (32-bit, non-prefetchable) [size=4K]
    Expansion ROM at feb80000 [disabled] [size=256K]
    Capabilities: [40] MSI-X: Enable+ Count=3 Masked-
    Kernel driver in use: virtio-pci

root@PC1:~# iperf -c 192.168.0.126 -d -t 30 -l 64
------------------------------------------------------------
Server listening on TCP port 5001
TCP window size: 85.3 KByte (default)
------------------------------------------------------------
------------------------------------------------------------
Client connecting to 192.168.0.126, TCP port 5001
TCP window size: 85.0 KByte (default)
------------------------------------------------------------
[  3] local 192.168.0.129 port 41573 connected with 192.168.0.126 port 5001
[  5] local 192.168.0.129 port 5001 connected with 192.168.0.126 port 44480
[ ID] Interval       Transfer     Bandwidth
[  3]  0.0-30.0 sec   126 MBytes  35.4 Mbits/sec
[  5]  0.0-30.0 sec   126 MBytes  35.1 Mbits/sec
root@PC1:~# 

Teste com e1000 ( 192.168.0.126 está configurado para T60 e 192.168.0.129 está configurado para PC1 ):

root@PC1:~# grep hype /proc/cpuinfo
flags       : fpu de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pse36 clflush mmx fxsr sse sse2 syscall nx lm rep_good nopl pni vmx cx16 x2apic hypervisor lahf_lm tpr_shadow vnmi flexpriority ept vpid
root@PC1:~# lspci -s 00:03.0 -v
00:03.0 Ethernet controller: Intel Corporation 82540EM Gigabit Ethernet Controller (rev 03)
    Subsystem: Red Hat, Inc QEMU Virtual Machine
    Physical Slot: 3
    Flags: bus master, fast devsel, latency 0, IRQ 11
    Memory at febc0000 (32-bit, non-prefetchable) [size=128K]
    I/O ports at c000 [size=64]
    Expansion ROM at feb80000 [disabled] [size=256K]
    Kernel driver in use: e1000

root@PC1:~# iperf -c 192.168.0.126 -d -t 30 -l 64
------------------------------------------------------------
Server listening on TCP port 5001
TCP window size: 85.3 KByte (default)
------------------------------------------------------------
------------------------------------------------------------
Client connecting to 192.168.0.126, TCP port 5001
TCP window size: 85.0 KByte (default)
------------------------------------------------------------
[  3] local 192.168.0.129 port 42200 connected with 192.168.0.126 port 5001
[  5] local 192.168.0.129 port 5001 connected with 192.168.0.126 port 44481
[ ID] Interval       Transfer     Bandwidth
[  3]  0.0-30.0 sec   126 MBytes  35.1 Mbits/sec
[  5]  0.0-30.0 sec   126 MBytes  35.1 Mbits/sec
root@PC1:~# 

Com pacotes grandes, a largura de banda era de ~ 900Mbps no caso de ambos os drivers.

Quando o maior desempenho teórico de virtio-pci entra em jogo? Por que vi desempenho igual com e1000 e virtio-pci ?