[PATCH] AArch64: Add hp-timing.h

[Szabolcs Nagy]

The 06/28/2021 13:06, Florian Weimer wrote:
> * Wilco Dijkstra:
> > Hi Florian,
> >> Is the MSR called cntcvt_el0 or cntvct_el0?
> >
> > cntvct_el0 - it's just a random combination of characters!
> 
> Okay, then please fix the other occurence that is a typo.
> 
> >> I'm clearly missing something: If this is broken on some kernels, how is
> >> this disabled?
> >
> > It's not enabled just to be extremely conservative - however I don't
> > believe this is an issue in practice since it works fine even on the
> > first AArch64 boards and servers.
> 
> I meant: How is this disabled in glibc on older kernels?  Or is this
> code just dormant as of now?

iirc linux devs asked that it is only used in vdso so
that it is under the kernel's control in case there
are implementation issues (vdso is easy to disable
and on some system it got disabled for timer reasons).

is hp-timing.h for some internal benchmarks only?

if no, then i think we should get the opinion of
linux maintainers before we use this in glibc.