RE: PCI passthrough with VT-d - native performance

Han, Weidong
2008-07-17T03:20:31Z

Anthony Liguori wrote:
> Ben-Ami Yassour wrote:
>> On Wed, 2008-07-16 at 17:36 +0300, Avi Kivity wrote:
>>
>>> Ben-Ami Yassour wrote:
>>>
>>>> In last few tests that we made with PCI-passthrough and VT-d using
>>>> iperf, we were able to get the same throughput as on native OS
>>>> with a 1G NIC
>>>>
>>> Excellent!
>>>
>>>
>>>> (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%
>>
>
> What about virtio? Also, which emulated is this?
>
> That CPU utilization is extremely high and somewhat illogical if
> native w/vt-d has almost no CPU impact. Have you run oprofile yet or
> have any insight into where CPU is being burnt?
>
> What does kvm_stat look like? I wonder if there are a large number of
> PIO exits. What does the interrupt count look like on native vs. KVM
> with VT-d?
>

e1000 NIC doesn't use PIO.

Randy (Weidong)