Re: [Qemu-devel] dropped pkts with Qemu on tap interace (RX)

[Stefan Priebe - Profihost AG]

Am 03.01.2018 um 04:57 schrieb Wei Xu:
> On Tue, Jan 02, 2018 at 10:17:25PM +0100, Stefan Priebe - Profihost AG wrote:
>>
>> Am 02.01.2018 um 18:04 schrieb Wei Xu:
>>> On Tue, Jan 02, 2018 at 04:24:33PM +0100, Stefan Priebe - Profihost AG 
>>> wrote:
>>>> Hi,
>>>> Am 02.01.2018 um 15:20 schrieb Wei Xu:
>>>>> On Tue, Jan 02, 2018 at 12:17:29PM +0100, Stefan Priebe - Profihost AG 
>>>>> wrote:
>>>>>> Hello,
>>>>>>
>>>>>> currently i'm trying to fix a problem where we have "random" missing
>>>>>> packets.
>>>>>>
>>>>>> We're doing an ssh connect from machine a to machine b every 5 minutes
>>>>>> via rsync and ssh.
>>>>>>
>>>>>> Sometimes it happens that we get this cron message:
>>>>>> "Connection to 192.168.0.2 closed by remote host.
>>>>>> rsync: connection unexpectedly closed (0 bytes received so far) [sender]
>>>>>> rsync error: unexplained error (code 255) at io.c(226) [sender=3.1.2]
>>>>>> ssh: connect to host 192.168.0.2 port 22: Connection refused"
>>>>>
>>>>> Hi Stefan,
>>>>> What kind of virtio-net backend are you using? Can you paste your qemu
>>>>> command line here?
>>>>
>>>> Sure netdev part:
>>>> -netdev
>>>> type=tap,id=net0,ifname=tap317i0,script=/var/lib/qemu-server/pve-bridge,downscript=/var/lib/qemu-server/pve-bridgedown,vhost=on
>>>> -device
>>>> virtio-net-pci,mac=EA:37:42:5C:F3:33,netdev=net0,bus=pci.0,addr=0x12,id=net0,bootindex=300
>>>> -netdev
>>>> type=tap,id=net1,ifname=tap317i1,script=/var/lib/qemu-server/pve-bridge,downscript=/var/lib/qemu-server/pve-bridgedown,vhost=on,queues=4
>>>> -device
>>>> virtio-net-pci,mac=6A:8E:74:45:1A:0B,nedev=net1,bus=pci.0,addr=0x13,id=net1,vectors=10,mq=on,bootindex=301
>>>
>>> According to what you have mentioned, the traffic is not heavy for the 
>>> guests,
>>> the dropping shouldn't happen for regular case.
>>
>> The avg traffic is around 300kb/s.
>>
>>> What is your hardware platform?
>>
>> Dual Intel Xeon E5-2680 v4
>>
>>> and Which versions are you using for both
>>> guest/host kernel
>> Kernel v4.4.103
>>
>>> and qemu?
>> 2.9.1
>>
>>> Are there other VMs on the same host?
>> Yes.
> 
> What about the CPU load? 

Host:
80-90% Idle
LoadAvg: 6-7

VM:
97%-99% Idle

>>>>> 'Connection refused' usually means that the client gets a TCP Reset rather
>>>>> than losing packets, so this might not be a relevant issue.
>>>>
>>>> Mhm so you mean these might be two seperate ones?
>>>
>>> Yes.
>>>
>>>>
>>>>> Also you can do a tcpdump on both guests and see what happened to SSH 
>>>>> packets
>>>>> (tcpdump -i tapXXX port 22).
>>>>
>>>> Sadly not as there's too much traffic on that part as rsync is syncing
>>>> every 5 minutes through ssh.
>>>
>>> You can do a tcpdump for the entire traffic from the guest and host and 
>>> compare
>>> what kind of packets are dropped if the traffic is not overloaded.
>>
>> Are you sure? I don't get why the same amount and same kind of packets
>> should be received by both tap which are connected to different bridges
>> to different HW and physical interfaces.
> 
> Exactly, possibly this would be a host or guest kernel bug cos than qemu issue
> you are using vhost kernel as the backend and the two stats are independent,
> you might have to check out what is happening inside the traffic.

What do you mean by inside the traffic?

Stefan