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I am using QEMU to virtualize KVM VPS. I have already turned off all the things like gso,tso,tx,rx at the host's network interface and my VPS use VirtIO as the NIC. When I do speedtest at the host, usually a result of approximately 800 Mbps downlink and 600 Mbps uplink. However, when I do the same test inside the VPS, only 300/200 Mbps can be obtained, as if something is limiting the speed to 300 Mbps. However after I check everything, I did not find the cause of the poor network performance.

Are there any way to further improve the network performance in the KVM VPS? My host is using double Xeon E5530 (8 Core 16 Threads) and has 64 GiB of physical memory and approximately 100 VPS (mostly 256 MiB Memory/1 Core) are running on it. Average load of the host is about 3.0. Both the host and the VPS is using the same NIC on the host and network bridge is correctly set up.

Howard Liu
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1 Answers1

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I was facing some problem in a Xen to KVM migration and studing the situation we got the next conclusions.

1.- Our best performance was obtained inserting some new NICs to the server and assigning a pci device to a VPS. You will get same performance as it was not virtualized.

Problems:

  • You need a VPS linked to a new external NIC controller.Pci passthrough.
  • You need one network controller for each port you want to configure. Search iommu information.
  • Forget live migrations between hosts with assigned pci's.

2.- Using virtio drivers and performance tunning.

We got better performance but impossible to compare with a pci-passthrough.

There are some researches from KVM people who say that they reach great performance, I can't say it is not true but I couldn't replicate that performance. http://www.linux-kvm.org/page/Using_VirtIO_NIC

Tunning: Following the next guide you can find some tips to get the best performance.

We noticed an important improve with Multi-Queue virtio-net approach but I guess It won't be useful for you if your VPS is using just one core.

https://access.redhat.com/documentation/en-US/Red_Hat_Enterprise_Linux/7/html/Virtualization_Tuning_and_Optimization_Guide/chap-Virtualization_Tuning_Optimization_Guide-Networking.html#sect-Virtualization_Tuning_Optimization_Guide-Networking-General_Tips

Ferrandinand
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  • Thanks for your reply. I think this problem is purely a performance problem caused by the over using of the CPU and some other resources. It can achieve a speed close to PCI-Passthrough but the more VPS hosting on it, it become slower. – Howard Liu Aug 22 '16 at 14:58