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[Qemu-discuss] network latency for virtio-net-pci

From: George Shuklin
Subject: [Qemu-discuss] network latency for virtio-net-pci
Date: Mon, 01 Sep 2014 18:18:27 +0300
User-agent: Mozilla/5.0 (X11; Linux i686; rv:31.0) Gecko/20100101 Thunderbird/31.0


We running qemu 1.5, and one of the users complains on high latency on the overlay network of openstack.

I done some research and comparation and found those numbers:

V - virtual machine with qemu/virtio-net-pci tap device.
H - hardware server
S - hardware switch
O - openvswitch bridge (OVS 2.0)

V-O-V - 300 µs
V-H - 180 µs
H-S-H - 140 µs
V-O-S-O-V - 600 µs

After doing some math with linear equations and few more tests I found following latencies:

internal linux latency - 50 µs
hardware switch latency - 40 µs
openvswitch (gre-mode) latency  40 µs

and, most important:

QEMU device - 130 µs

It looks really slow.

My questions:

1. Is newer versions of qemu showing better lattency? (If possible, show me please your V-to-V ping on same host)
2. Is any way to reduce latency for qemu network devices?


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