Re: [Xen-users] XEN - Broadcom issue: survey

[Pasi Kärkkäinen <pasik@xxxxxx>]

On Wed, Nov 14, 2007 at 03:17:07PM +0000, Steven Smith wrote:
> > this driver is the one relased by DELL on Nov. 11, and I have packet drop. 
> > The same with driver 1.5.1c from broadcom
> >
> > The strange thing is that TX-DRP is 0 until I start a domain. Since I start 
> > an HVM, TX-DRP for its vif start incresing.
> >
> > If I start an PV machine, it drop only 20 packets and then stop. No more 
> > TX-DRP at all...
> Yes, that's normal and expected behaviour.  If you try and send a
> packet over a PV network interface to a domain which hasn't loaded the
> PV network driver, the packet will be dropped and the TX-DRP statistic
> will be incremented.  PV domains will therefore see a small number of
> packets dropped at boot time, while HVM domains will see ongoing
> packet drop for as long as the domain remains alive.  For an HVM
> domain, you probably want to look at the tap device rather than the
> vif.
> 

Steps to go through to debug:

1. Make sure networking is OK in the host, without running xen at all
(just running the normal non-xen kernel).

2. Make sure networking is OK on dom0, when running xen-kernel and NO domU
   running. 

3. Make sure networking is OK on paravirt domU.

4. Make sure networking is OK on HVM domU, make sure you're running 
   paravirt drivers on HVM domU (this is important!!). Without PV drivers
   performance of HVM domU will be sucky and you WILL get packet drops.

Now, with those tests done, you should be able to isolate the problem quite
easily.. and see if it's NIC/driver or Xen or domU driver related.

-- Pasi 

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