Re: PCI passthrough with VT-d - native performance

[Avi Kivity <avi@qumranet.com>]

Ben-Ami Yassour wrote:
>>>  (with higher CPU utilization).
>>>   
>>>       
>> How much higher?
>>     
>
> Here are some numbers for running iperf -l 1M:
>
> e1000 NIC (behind a PCI bridge)
>                        Bandwidth (Mbit/sec)    CPU utilization
> Native OS                   771                      18%
> Native OS with VT-d         760                      18% 
> KVM VT-d                    390                      95% 
> KVM VT-d with direct mmio   770                      84%
> KVM emulated                 57                     100%  
>
> Comment: its not clear to me why the native linux can not get closer to 1G for this NIC,
> (I verified that its not external network issues). But clearly we shouldn't hope to 
> get more then the host does with a KVM guest (especially if the guest and host are the 
> same OS as in this case...).
>
> e1000e NIC (onboard)
>                        Bandwidth (Mbit/sec)    CPU utilization
> Native OS                   915                      18%
> Native OS with VT-d         915                      18%
> KVM VT-d with direct mmio   914                      98%
>
> Clearly we need to try and improve the CPU utilization, but I think that this is good enough 
> for the first phase.
>
>   

Agree;  part of the higher utilization is of course not the fault of the 
device assignment code, rather it is ordinary virtualization overhead.  
We'll have to tune this.

-- 
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