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

[Andrii Anisov <andrii.anisov@xxxxxxxxx>]

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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