Collecting hypervisor call stats

[Segher Boessenkool]

> Can you explain the need for barrier(s) before and after the call  
> to the
> real routine?  It usually takes me a couple days of thought to  
> figure out
> exactly where these are needed. :)

The barriers make the timing ever so slightly more deterministic (not  
more
"accurate" though), because it has a "sync" insn in it.  The sc insn  
to do
the actual hypervisor call is a synchronisation point itself of  
course, as
probably some things around it are as well.  So just blast-em away,  
they do
slow down things, and you don't really care about a few cycles more  
or less
reported, hypervisor calls are not that fast.


Segher