Re: [Qemu-devel] ping latency issue on passthrough guest

[Zhu Yijun]

Hi Alex,

    Thanks for your reply, I will try to assign PF to VM and test.

2018-05-11 22:26 GMT+08:00 Alex Williamson <address@hidden>:
> On Fri, 11 May 2018 15:20:05 +0800
> Zhu Yijun <address@hidden> wrote:
>
>> Hi all,
>>
>>   I booted two sr-iov guests using KVM-VFIO and pinged each other with
>> no-load one night. I found that most of the latency was little than 0.1ms,
>> but several icmp_seq greater than 10ms, even up to 1000ms;
>>
>>   address@hidden:~# grep "time=[0-9][0-9]" outputfile
>> Mon May  7 23:05:12 201864 bytes from 192.168.0.200: icmp_seq=16703 ttl=64
>> time=123 ms
> ...
>>
>>    VF used by these two guest from same port(eth0) of intel X710 Ethernet
>> controller. By contrast, I selected another two VFs and set them to
>> separate network namespace, this issue did not exits, all the latency
>> litter than 0.2ms.
>
> I think you've proved by this experiment that it's not likely to be a
> device assignment issue.  Device assignment knows nothing about the
> device above the base PCI level operation, so if changing the
> networking configuration resolves the issue, the problem is perhaps
> more likely in how the PF, or maybe the guest itself, is routing VF
> packets.  Thanks,
>
> Alex