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Re: [Xen-devel] [PATCH v3] xen: introduce VCPUOP_register_runstate_phys_memory_area hypercall





On 14.06.19 18:24, Julien Grall wrote:
I hope you are aware that speaking about speed here is quite irrelevant. The 
difference would be clear lost in the noise of the rest of the context switch.

Mmm... I have that understanding. Yet I'd rather try to not increase the noise, 
if not reduce.

BTW, I'll remember that to you on your next conditional branch removal ;)

But, if you allow something, then most likely someone will use it. However, you 
have to differentiate implementation vs documentation.

In this case, I don't think the implementation should dictate what is going to 
be exposed.

If you document that it can't happen, then you have room to forbid the mix in 
the future (assuming this can't be done now).

In other word, the more lax is the interface, the more difficult it is tighten 
in the future.

I am not going to push for an implementation that forbid the mix. But I am 
strongly going to push for any documentation of the expected interaction. So we 
don't make our life miserable later on.

I do not encourage using both interfaces simultaneously, it is pointless.
If you are saying that this matter could be solved with the appropriate 
documentation, it's OK with me.

BTW, dropping the old interface implementation will be much easier in future if 
it will not clash with the new one.
I am afraid we will never be able to remove the old interface.

Maybe.

--
Sincerely,
Andrii Anisov.

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