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Re: [Xen-users] strange ethtool output in xen environment
On 12/11/09 12:59, Fasiha Ashraf wrote:
I want to check the speed like features of my Ethernet in
dom0 and domUs. But in virtualized environment it gives strange output
why is that so? how to check it otherwise?
Non-virtualized
FC11
[root@fasiha home]# ethtool eth0
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The question makes no sense, really. The speed of a NIC is dependent
on physical characteristics: the speed at which it can generate and
observe a signal. A virtual NIC doesn't have those physical
characteristics and the emulated NIC in a domU doesn't know what
physical hardware is going to actually send or receive signals. A
virtual NIC can report a speed, but if it does, it's just lying so that
it can give some plausible answer.
In dom0 you do have access to the physical NIC: it might be eth0 but it
might be something else. On different machines, "eth0" might be
different things depending on how the bridge is set up. On a
reasonably "standard" xen 3.4.0 eth0 is a bridge and the NIC is peth0
(you can see that from brctl show). Bridges don't correspond to NICs
so "ethtool eth0" is relatively useless.
In domU you have a virtual NIC and since ethtool is reporting physical
characteristics, anything you might or might not see is made up by the
driver.
jch
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