Re: PV on HVM network stops

[Ryan Harper <ryanh@us.ibm.com>]

* Ian Pratt <Ian.Pratt@cl.cam.ac.uk> [2007-05-09 18:46]:
> > > Presumably taking the guest interface down makes no difference? (Not
> > > sure you can unload the module, but have you tried?)
> > 
> > I tried.  It doesn't completely work, I'll get the dmesg output again
> > for future reference.  Reloading the module didn't help as it set the
> > device mac add to all nulls.
> 
> It should be able to read the MAC from xenstore. This must be a bug.
> 
> > > > Using tcpdump, I can see traffic arrive in the domain, but no
> > traffic
> > > > leaves the guest.
> > >
> > > So, packets seem to be received by the guest, but if you tcpdump the
> > > associated vifX.0 you don't see anything (whereas a tcpdump in the
> > guest
> > > indicates packets are being sent).
> > 
> > tcpdump on vifX.0 shows traffic on the bridge, arps for the guest ip.
> > tcpdump in the guest showed it getting the arps, but no reply.  ie, no
> > outgoing traffic.
> 
> Hang on, you mean within the guest you don't see it sending a reply? If
> true, that must be a guest issue and its hard to see how doing anything
> in dom0 will help.

I'm not sure if there the networking is the real problem.  The trouble
is that in many cases when the networking chokes, the console is hosed
as well which makes it rather difficult to capture tcpdump from within.

The next time networking is down but console is up, I'll confirm the
tcpdump from the guest.

> 
>  
> > I've worked around this issue by cycling the vif in the host.
> > 
> > What I am seeing now is that sometimes the guest just doesn't seem to
> > be making progress, no cpu time.  xm console the guest hangs any new
> > processes don't seem to execute.  For example, I can have a console
> > session connected and watch networking die, cycle the vif, pings start
> > working again, and running ps in the guest just blocks.  xm list shows
> > the guest in the block state.  At this point, the guest is pretty much
> > dead even though it will continue to process ICMP packets.
> 
> That sounds like a symptom of the block devices being wedged. Are you
> using a PV block device or emulated IDE?

using PV block.


-- 
Ryan Harper
Software Engineer; Linux Technology Center
IBM Corp., Austin, Tx
(512) 838-9253   T/L: 678-9253
ryanh@us.ibm.com