Re: Bandwith limitation with KVM VMs

[Daniel Bareiro <daniel-listas@gmx.net>]

[-- Attachment #1: Type: text/plain, Size: 2589 bytes --]

Hi Gregory.

On Monday, 03 August 2009 12:52:28 -0400,
Gregory Haskins wrote:

> > 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.

> 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.

It draws attention that when executing 'cfgmaker' from MRTG server
against the IP of the VM, it returns max speed of 1250 kBytes/s, that
is to say 10 Mbps:

sparky:~# /usr/bin/cfgmaker --global 'WorkDir: /tmp' --global \ 
 'Options[_]: bits,growright' xxxxxxxxxxxxxx@10.1.0.42
[...]
MaxBytes[10.1.0.42_2]: 1250000


But nevertheless from within of the VM I see the following thing:

aps2:~# ethtool eth0
Settings for eth0:
        Supported ports: [ TP MII ]
        Supported link modes:   10baseT/Half 10baseT/Full
                                100baseT/Half 100baseT/Full
        Supports auto-negotiation: Yes
        Advertised link modes:  10baseT/Half 10baseT/Full
                                100baseT/Half 100baseT/Full
        Advertised auto-negotiation: Yes
        Speed: 100Mb/s
        Duplex: Full
        Port: MII
        PHYAD: 32
        Transceiver: internal
        Auto-negotiation: on
        Supports Wake-on: pumbg
        Wake-on: d
        Current message level: 0x00000007 (7)
        Link detected: yes


do you think that can give some indication?

Thanks for your reply.

Regards,
Daniel
-- 
Fingerprint: BFB3 08D6 B4D1 31B2 72B9  29CE 6696 BF1B 14E6 1D37
Powered by Debian GNU/Linux Squeeze - Linux user #188.598

[-- Attachment #2: Digital signature --]
[-- Type: application/pgp-signature, Size: 197 bytes --]