[ovirt-users] Strange network performance on VirtIIO VM NIC
FERNANDO FREDIANI
fernando.frediani at upx.com
Mon Mar 20 15:14:13 UTC 2017
Hello Yaniv.
It also looks to me initially that for 1Gbps multi-queue would not be
necessary, however the Virtual Machine is relatively busy where the CPU
necessary to process it may (or not) be competing with the processes
running on in the guest.
The network is as following: 3 x 1 Gb interfaces bonded together with
layer2+3 has algorithm where the VMs connect to the outside world.
vNIC1 and vNIC2 in the VMs are the same VirtIO NIC types. These vNICs
are connected to the same VLAN and they are both able to output 1Gbps
throughput each at the same time in iperf tests as the bond below has
3Gb capacity.
Please note something interesting I mentioned previously: All traffic
currently goes in and out via vNIC1 which is showing packet loss (3% to
10%) on the tests conducted. NIC2 has zero traffic and if the same tests
are conducted against it shows 0% packets loss.
At first impression if it was something related to the bond or even to
the physical NICs on the Host it should show packet loss for ANY of the
vNICs as the traffic flows through the same physical NIC and bond, but
is not the case.
This is the qemu-kvm command the Host is executing:
/usr/libexec/qemu-kvm -name guest=VM_NAME_REPLACED,debug-threads=on -S
-object
secret,id=masterKey0,format=raw,file=/var/lib/libvirt/qemu/domain-6-VM_NAME_REPLACED/master-key.aes
-machine pc-i440fx-rhel7.3.0,accel=kvm,usb=off -cpu SandyBridge -m 4096
-realtime mlock=off -smp 4,maxcpus=16,sockets=16,cores=1,threads=1 -numa
node,nodeid=0,cpus=0-3,mem=4096 -uuid
57ffc2ed-fec5-47d6-bfb1-60c728737bd2 -smbios
type=1,manufacturer=oVirt,product=oVirt
Node,version=7-3.1611.el7.centos,serial=4C4C4544-0043-5610-804B-B1C04F4E3232,uuid=57ffc2ed-fec5-47d6-bfb1-60c728737bd2
-no-user-config -nodefaults -chardev
socket,id=charmonitor,path=/var/lib/libvirt/qemu/domain-6-VM_NAME_REPLACED/monitor.sock,server,nowait
-mon chardev=charmonitor,id=monitor,mode=control -rtc
base=2017-03-17T01:12:39,driftfix=slew -global
kvm-pit.lost_tick_policy=discard -no-hpet -no-shutdown -boot strict=on
-device piix3-usb-uhci,id=usb,bus=pci.0,addr=0x1.0x2 -device
virtio-scsi-pci,id=scsi0,bus=pci.0,addr=0x7 -device
virtio-serial-pci,id=virtio-serial0,max_ports=16,bus=pci.0,addr=0x5
-drive if=none,id=drive-ide0-1-0,readonly=on -device
ide-cd,bus=ide.1,unit=0,drive=drive-ide0-1-0,id=ide0-1-0 -drive
file=/rhev/data-center/2325e1a4-c702-469c-82eb-ff43baa06d44/8dcd90f4-c0f0-47db-be39-5b49685acc04/images/ebe10e75-799a-439e-bc52-551b894c34fa/1a73cd53-0e51-4e49-8631-38cf571f6bb9,format=qcow2,if=none,id=drive-scsi0-0-0-0,serial=ebe10e75-799a-439e-bc52-551b894c34fa,cache=none,werror=stop,rerror=stop,aio=native
-device
scsi-hd,bus=scsi0.0,channel=0,scsi-id=0,lun=0,drive=drive-scsi0-0-0-0,id=scsi0-0-0-0,bootindex=1
-drive
file=/rhev/data-center/2325e1a4-c702-469c-82eb-ff43baa06d44/8dcd90f4-c0f0-47db-be39-5b49685acc04/images/db401b27-006d-494c-a1ee-1d37810710c8/664cffe6-52f8-429d-8bb9-2f43fa7a468f,format=qcow2,if=none,id=drive-scsi0-0-0-1,serial=db401b27-006d-494c-a1ee-1d37810710c8,cache=none,werror=stop,rerror=stop,aio=native
-device
scsi-hd,bus=scsi0.0,channel=0,scsi-id=0,lun=1,drive=drive-scsi0-0-0-1,id=scsi0-0-0-1
-netdev tap,fd=33,id=hostnet0,vhost=on,vhostfd=36 -device
virtio-net-pci,netdev=hostnet0,id=net0,mac=00:1a:4a:16:01:60,bus=pci.0,addr=0x3
-netdev tap,fd=37,id=hostnet1,vhost=on,vhostfd=38 -device
virtio-net-pci,netdev=hostnet1,id=net1,mac=00:1a:4a:16:01:61,bus=pci.0,addr=0x4
-chardev
socket,id=charchannel0,path=/var/lib/libvirt/qemu/channels/57ffc2ed-fec5-47d6-bfb1-60c728737bd2.com.redhat.rhevm.vdsm,server,nowait
-device
virtserialport,bus=virtio-serial0.0,nr=1,chardev=charchannel0,id=channel0,name=com.redhat.rhevm.vdsm
-chardev
socket,id=charchannel1,path=/var/lib/libvirt/qemu/channels/57ffc2ed-fec5-47d6-bfb1-60c728737bd2.org.qemu.guest_agent.0,server,nowait
-device
virtserialport,bus=virtio-serial0.0,nr=2,chardev=charchannel1,id=channel1,name=org.qemu.guest_agent.0
-chardev spicevmc,id=charchannel2,name=vdagent -device
virtserialport,bus=virtio-serial0.0,nr=3,chardev=charchannel2,id=channel2,name=com.redhat.spice.0
-vnc 192.168.100.19:2,password -k pt-br -spice
tls-port=5903,addr=192.168.100.19,x509-dir=/etc/pki/vdsm/libvirt-spice,tls-channel=default,tls-channel=main,tls-channel=display,tls-channel=inputs,tls-channel=cursor,tls-channel=playback,tls-channel=record,tls-channel=smartcard,tls-channel=usbredir,seamless-migration=on
-k pt-br -device
qxl-vga,id=video0,ram_size=67108864,vram_size=33554432,vram64_size_mb=0,vgamem_mb=16,bus=pci.0,addr=0x2
-incoming defer -device
virtio-balloon-pci,id=balloon0,bus=pci.0,addr=0x6 -object
rng-random,id=objrng0,filename=/dev/urandom -device
virtio-rng-pci,rng=objrng0,id=rng0,bus=pci.0,addr=0x8 -msg timestamp=on
Load in the VM is relatively high (20 to 30) and CPU usage is between
50% to 60% with eventual peaks of 100% in one of the vCPUs. There is a
lot of processes running in the VM similar to Web Servers which is using
this amount of CPU.
Only guess I could have so far is that traffic on NIC1 is being handeled
by one of the vCPUs which eventually get 100% due to some of the
processes while traffic on NIC2 is handled by another vCPU which is not
that busy and explains the 0% packet loss. BUT, should VirtIO vNIC use
CPU from within the Guest ?
Does it make any sense ?
Thanks
Fernando
On 18/03/2017 12:53, Yaniv Kaul wrote:
>
>
> On Fri, Mar 17, 2017 at 6:11 PM, FERNANDO FREDIANI
> <fernando.frediani at upx.com <mailto:fernando.frediani at upx.com>> wrote:
>
> Hello all.
>
> I have a peculiar problem here which perhaps others may have had
> or know about and can advise.
>
> I have Virtual Machine with 2 VirtIO NICs. This VM serves around
> 1Gbps of traffic with thousands of clients connecting to it. When
> I do a packet loss test to the IP pinned to NIC1 it varies from 3%
> to 10% of packet loss. When I run the same test on NIC2 the packet
> loss is consistently 0%.
>
> From what I gather I may have something to do with possible lack
> of Multi Queu VirtIO where NIC1 is managed by a single CPU which
> might be hitting 100% and causing this packet loss.
>
> Looking at this reference
> (https://fedoraproject.org/wiki/Features/MQ_virtio_net
> <https://fedoraproject.org/wiki/Features/MQ_virtio_net>) I see one
> way to test it is start the VM with 4 queues (for example), but
> checking on the qemu-kvm process I don't see option present. Any
> way I can force it from the Engine ?
>
>
> I don't see a need for multi-queue for 1Gbps.
> Can you share the host statistics, the network configuration, the
> qemu-kvm command line, etc.?
> What is the difference between NIC1 and NIC2, in the way they are
> connected to the outside world?
>
>
> This other reference
> (https://www.linux-kvm.org/page/Multiqueue#Enable_MQ_feature
> <https://www.linux-kvm.org/page/Multiqueue#Enable_MQ_feature>)
> points to the same direction about starting the VM with queues=N
>
> Also trying to increase the TX ring buffer within the guest with
> ethtool -g eth0 is not possible.
>
> Oh, by the way, the Load on the VM is significantly high despite
> the CPU usage isn't above 50% - 60% in average.
>
>
> Load = latest 'top' results? Vs. CPU usage? Can mean a lot of
> processes waiting for CPU and doing very little - typical for web
> servers, for example. What is occupying the CPU?
> Y.
>
>
> Thanks
> Fernando
>
>
>
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