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Re: [Xen-devel] 32/64-bit hypercall interface

On Monday 03 October 2005 14:56, Ian Pratt wrote:
> [*] implementing a hypercall compat layer is trivial compared to other
> overheads you'd have (like shadow page tables).

I agree with this statement.

However, doesn't that same argument apply to correcting the ABI in the first 
place? Shadow page tables will overshadow the performance impact of making 
the ABI 32/64-bit clean.

In fact, even a plain old hypercall will also overshadow that performance 
impact, both in terms of cycle count and cache footprint.

So if your choice then is between a compatibility translation layer and 
altering the interface, I think it's pretty clear that changing the interface 
will result in the least amount of additional code (and associated long-term 
code maintenance).

Hollis Blanchard
IBM Linux Technology Center

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