Re: Xen emulated network cards (was Re: FreeBSD HVM guests?)

["Jonathan A. Kollasch" <jakllsch%kollasch.net@localhost>]

On Wed, May 20, 2009 at 03:57:17PM -0400, Thor Lancelot Simon wrote:
> On Wed, May 20, 2009 at 07:58:10PM +0100, Stephen Borrill wrote:
> >
> > The qemu 0.9.1 man page says:
> > Qemu can emulate several different models of network card.  Valid values 
> > for type are "i82551", "i82557b", "i82559er", "ne2k_pci", "ne2k_isa", 
> > "pcnet", "rtl8139", "smc91c111", "lance" and "mcf_fec".
> >
> > I guess any of these are potential alternatives to e1000 on xen 3.1.4, 
> > but are any of them any better than ne2k_pci?
> 
> Any of 82551, 82557, or 82559 should work with the 'fxp' driver.  They
> have a reasonable DMA interface (ne2k_pci is so slow because it uses PIO,
> which must be emulated on a word-by-word basis!) and should be acceptably
> fast.
> 
> "pcnet" should work with our "pcn" or "le" drivers and "lance" should
> work with our "le" driver.  I have noticed some problems with emulated
> pcnet devices in the past, though.  The main advantage to using pcn
> instead of le is a larger dma descriptor ring.
> 
> A few of these devices may support interrupt mitigation, which would
> further reduce emulation overhead, but I fear none of our drivers do.
> That, plus TSO, would be the big win to using an emulated e1000.

One caveat, qemu's e1000 doesn't act enough like the chip it says it is
for wm(4) to work. Also, the qemu eepro100 falls over when it's touched
by our fxp(4).

        Jonathan Kollasch