[Xen-ia64-devel] RE: Implementing both (was: Xen/ia64 - global or per VP VHPT)

["Munoz, Alberto J" <alberto.j.munoz@xxxxxxxxx>]

Hi Dan,

The first thing I want to ask is whether or not you are proposing that both
mechanisms be present at run time. I definitely don't think that is the
right thing to do, as then we will have the worst of both worlds, a global
VHPT that needs to be dimensioned to the full size of memory and the per VM
VHPTs that would be requiring additional memory.

I have no objection to both solutions being implemented in the sources and
having the ability to pick one or the other (through #ifdef). This should
make it easy to compare which one does better (in most cases) and would make
it very easy to drop the one that does not.

Bert

Magenheimer, Dan (HP Labs Fort Collins) <mailto:dan.magenheimer@xxxxxx>
wrote on Monday, May 02, 2005 4:34 PM:

> Thanks, Bert, for the good summary of issues.
> 
>> If everyone agrees that doing both
>> implementations in the same source base is feasible and does
>> not adversely
>> affect other stuff, then I have no objection to what you propose.
> 
> Let's start the feasibility discussion on a new base thread...
> 
> I am probably oversimplifying it, but I'm not sure it will be
> that hard to support both approaches.  Domain0's VHPT is set
> up at boot time.  When new domains are launched they should
> specify whether they want to "share" Domain0's VHPT (global
> VHPT) or have their own VHPT allocated (per-domain VHPT).
> For now, the default for paravirt domains can be shared and
> the default (or, if necessary, the ONLY choice) for VT domains
> can be per-domain.
> 
> The choice (and the location of the physical IVA) becomes
> part of the per-domain state.  At domain switch time, cr.iva
> is changed as necessary.
> 
> Now everybody can commence shooting holes in my oversimplification :-)
> 
> Dan

Bert

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