Collecting hypervisor call stats

[Paul Mackerras]

Mike Kravetz writes:

> We would like to add code that gathers statistics about hypervisor calls.
> It would keep track of things like # of calls made for each opcode as well
> as time spent processing the calls.
> 
> The 'obvious' place to gather such statistics would be from within the
> routines making hcalls in hvCall.S.  Once thing that I have noticed is
> the following comment at the beginning hvCall.S:
> 
>  * NOTE: this file will go away when we move to inline this work.

I suspect that's a very old comment. :)

> So, it appears someone thought/thinks these routines should be inlined.  
> I assume this is for performance reasons?  If this is the case, then I
> suspect gathering of statistics (which would introduce overhead) would
> meet resistance?
> 
> Comments about the feasibility of adding such statistic gathering code
> would be appreciated.

I think that gathering those statistics would be useful.  I suggest
you use a per-cpu array for them, to reduce the performance impact.

Paul.