Re: [Xen-devel] domU to domU networking issues in v3.7? (netserver/netperf failing to communicate)

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Sat, 2012-11-10 at 13:59 +0000, Konrad Rzeszutek Wilk wrote:
> Hey Ian, Xen-devel mailingl list,
> 
> I think the issue of 70% traffic lost was actually introduced in v3.6 or
> perhaps v3.5. Annie and Marcos (CC-ed here) are looking to see which of
> the releases introduced this. The issue we are seeing is that a domU
> to domU communication breaks - this is with netperf/netserver talking to
> each other.
> 
> Anyhow, I think the 3.7 compound page exacerbated the problem and also
> (at least on some of my test hardware) exposed existing issues with
> drivers. The issue I have is that the 'skge' driver has a bug that has
> been there for ages (I tested way back to 3.0 and still saw it) were it
> can not work with SWIOTLB. It is probably missing an pci_dma_sync
> somewhere. 
> 
> Anyhow the compound page got me to look at Xen-SWIOTLB and that looks
> OK. Even with synthetic driver (the fake one I posted somewhere) it
> dealt with compound pages properly (with debug or non-debug Xen
> hypervisor).

The debug build is probably most interesting since it deliberately
allocates a non 1-1 p-to-m mapping so as to catch exactly these sorts of
issues.

> So was wondering if you had looked at this in more details? Any
> ideas? Or would it be more prudent to ask that once we know for sure
> which Linux release introduced the communication failures between
> guests?

I've not looked at it any further I'm afraid.

If these changes (be they in 3.5 or later, or earlier) are exposing
driver bugs then I suspect the netdev chaps would want to know about it.

FWIW I see the issue with tg3.

Ian.


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