Re: [Xen-users] Improve speed virtual machine

[Pasi Kärkkäinen <pasik@xxxxxx>]

On Sun, Aug 28, 2011 at 09:38:47AM +0100, Simon Hobson wrote:
> Bruno Steven wrote:
>
>> I have XEN 3.3 on Centos 5.4, my network interface have link 1 Gbps I 
>> want improve speed of network interface on virtual machine, from  
>> 100Mbps to 1Gpbs.
>
> AFAIK there is no 100Mbps limit on DomU virtual NICs. They may show up in 
> DomU as 100M but that's just an emulated NIC and not real hardware. I 
> think the only limit is the speed of the real NICs and the ability of 
> Dom0 to process packets.
>
> I think this latter bit is the most likely. I believe the code is single 
> threaded and there have been lots of threads on this list over the years 
> about poor network performance in DomUs
>

Yep, sounds like you're using the emulated realtek rtl8139 nic in the VM.
It reports 100 Mbps but it's NOT limited to 100 Mbps, because it's virtual nic.

Then again rtl8139 is quite crappy, even when emulated, so you might want to
switch to intel e1000 vnic (model=e1000). It's the fastest emulated nic.

Even better is of course to use Xen PVHVM drivers (PV-on-HVM),
where you don't have any kind of emulation, just straight PV drivers talking
directly to Xen.

-- Pasi


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