Re: Bandwith limitation with KVM VMs

[Gregory Haskins <gregory.haskins@gmail.com>]

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Daniel Bareiro wrote:
> Hi all!
> 
> I have a KVM VM that it has installed a MRTG on the network interface
> and that it doesn't register more than 10 Mbps, seeming that per moments
> it is saturated in this value.
> 
> Has KVM some bandwidth limitation of the virtualized network interfaces?
> In such case, exists some way to increase that limitation?
> 

There is no set artificial limit afaict, though there are a large number
of factors that can affect performance.  Of course, everything has an
ultimate ceiling (KVM included) but I have found this limit in KVM to be
orders of magnitude faster than 10Mbps.   Properly tuned, you should
easily be able to saturate a GE link at line rate, or even 4Gbps-5Gpbs
of a 10GE link.

If you need even more than that, I would suggest taking a look at my
recently announced project which focuses on IO performance:

http://developer.novell.com/wiki/index.php/AlacrityVM

However, since you are only hitting 10Mb/s now, there is ton of headroom
left even on upstream KVM so you might find it to be satisfactory as is,
once you address the current bottleneck in your setup.

Things to check:  What linkspeed does the host see to the next hop?  How
much bandwidth does the host see to the same end-point?  What is your
overall topology, especially for the VM (are you using -net tap, etc).
What MTU are you using.  Etc.

Good luck!
-Greg


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