Re: FOR REVIEW: New x86-64 vsyscall vgetcpu()

[Andi Kleen <ak@suse.de>]

> To this last point, it might be more reasonable to map in a page that
> contained a new structure with a stable ABI, which mirrored some of
> the task_struct information, and likely other useful information as
> needs are identified in the future.  In any case, it would be hard
> to beat a single memory read for performance.

That would mean making the context switch and possibly other
things slower. 

In general you would need to make a very good case first that all this 
complexity is worth it.

> Cache-coloring and kernel bookkeeping effects could be minimized if this 
> was provided as an mmaped page from a device driver, used only by
> applications which care.

I don't see what difference that would make. You would still
have the fixed offset problem and doing things on demand often tends 
to be even more complex.


-Andi (who thinks these proposals all sound very messy)