[PATCH] AArch64: Add hp-timing.h

[Adhemerval Zanella]

On 28/06/2021 08:49, Szabolcs Nagy via Libc-alpha wrote:
> 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.
> 

The patch sets HP_TIMING_INLINE to 0, so it is only used on benchmarks.