Re: suggested vhost link speed settings

[Michael Tokarev <mjt@tls.msk.ru>]

28.11.2010 05:26, linux_kvm@proinbox.com wrote:
> Hi list,
> 
> Being that the virtio interfaces are stated as acheiving 5-8 Gb
> throughput now with vhost, as opposed to 1Gb without, how should their
> link speed be defined when the choices are 2500M or 10000M?

The reported link speed for _any_ virtual NIC has no meaning at all,
except of the numbers somewhere in ifconfig or equivalent.  The actual
speed is always limited by the host CPU and the effectiveness of the
implementation currently in use.  So, it is merely a cosmetic thing,
nothing more.

The only possible usage for this number (reported link speed) is to
let some visualisation tools to draw their graphs, to show "link
utilisation" percentage for example.  But for that, there's no actual
utilisation either - it depends on the current host CPU speed, - f.e.
you put additional load to the CPU and the max speed will be lower,
but your visualisator will report low utilization.

In short: don't try to visualize "link utilization", it has no meaning.

As of actual speeds, I can reach ~2Gbps on my somewhat-old-now 2.4GHz
Phenom 9750 (first gen) even without vhost-net.

/mjt