RE: Transparent paravirtualization vs. xen paravirtualization(was:RE: [Xen-ia64-devel] IRQ management)

["Magenheimer, Dan (HP Labs Fort Collins)" <dan.magenheimer@xxxxxx>]

> The community should try to reduce recurrent effort.

I agree entirely but I think the correct way to do this is
to determine and implement a proper interface between
arch-dep and arch-neutral functionality for Xen, as was done on
Linux.  We were successful at doing this for the core hypervisor.
We need to do this for drivers too.

> Key issue on
> gnttab is Domain0 should also have PMT table support, which shouldn't
> access machine physical with gpn=mpn directly.  This issue is also the
> key reason causing major effort in porting VBD/DomainU for 
> each upstream
> merge.  This also blocks the forward VNIF effort due to page flipping
> issue.
> PMT is a must for gnttab to support VBD, VNIF and forward 
> development of
> Xen/ia64.   PMT would need to be shared between Domain and Xen for
> performance

I guess I disagree.  I've seen all the patches for each upstream
merge and it doesn't look to me as if a major design change
is required, just a clarification of the arch-specific boundaries.

Could you explain what you mean by "blocks the forward VNIF effort
due to page flipping issue"?  Page flipping should work just fine
in the current design; Matt had it almost working (out of tree)
before he went back to school.

> > By fixing irq handling and clearly understanding and properly
> > implementing architectural neutrality in event channels and
> > grant tables, I think we will eliminate most of the rebasing
> > difficulties.
> Key issue is Xen/ia64 shouldn't derail from basic grant table design

I don't see that it is significantly different.  We moved to
a separate file only as a temporary measure because there were
a handful of x86-specific lines of code in the core gnttab.c.
Unfortunately, we have not yet merged back, and that is the
source of some of the upstream merge issues.

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