> Would sgdt not be sufficient? I agree that we will have to end up
> giving RO access to user for the gdt page.
I meant exporting the GDT page
> I agree that we should not overload a single call (though cpu, package
> and node numbers do belong in one category IMO). We can have multiple
> calls if that is required as long as there is an efficient mechanism to
> provide that information.
The current mechanism doesn't scale to much more calls, but I guess
i'll have to do a vDSO sooner or later.
> Why maintain that extra logic in user space when kernel can easily give
> that information.
It already does.
> > I've been pondering to put some more information about that
> > in the ELF aux vector, but exporting might work too. I suppose
> > exporting would require the vDSO first to give a sane interface.
> >
> Can you please tell me what more information you are thinking of putting
> in aux vector?
One proposal (not fully fleshed out was) number of siblings / sockets / nodes
I don't think bitmaps would work well there (and if someone really needs
those they can read cpuinfo again)
This is mostly for OpenMP and tuning of a few functions (e.g. on AMD
the memory latencies varies with the number of nodes so some functions
can be tuned in different ways based on that)
> You are absolutely right that the mechanism I'm proposing makes sense
> only if we have more fields AND if any of those fields are dynamically
> changing. But this is a generic mechanism that could be extended to
> share any user visible information in efficient way. Once we have this
> in place then information like whole cpuinfo, percpu interrupts etc. can
> be retrieved easily.
The problem with exposing too much is that it might be a nightmare
to guarantee a stable ABI for this. At least it would
constrain the kernel internally. Probably less is better here.
Also I'm still not sure why user space should care about interrupts?
-Andi
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