[PATCH 6/6] aarch64: Add hp-timing.h

[Andrew Pinski]

On Sat, Jun 20, 2015 at 8:09 PM,  <pinskia@gmail.com> wrote:
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>
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>> On Jun 20, 2015, at 7:20 PM, Carlos O'Donell <carlos@redhat.com> wrote:
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>>> On 07/21/2014 02:31 PM, Marcus Shawcroft wrote:
>>>> On 21 July 2014 13:01, Andreas Schwab <schwab@suse.de> wrote:
>>>> pinskia@gmail.com writes:
>>>>
>>>>>> On Jul 21, 2014, at 4:41 AM, Andreas Schwab <schwab@suse.de> wrote:
>>>>>>
>>>>>> Richard Henderson <rth@twiddle.net> writes:
>>>>>>
>>>>>>> +/* Sync the instruction stream, and read from the virtual cycle counter.  */
>>>>>>> +#define HP_TIMING_NOW(Var) \
>>>>>>> +  __asm__ __volatile__ ("isb; mrs %0, cntvct_el0" : "=r" (Var))
>>>>>>
>>>>>> According to https://bugs.launchpad.net/bugs/1344320 the generic timers
>>>>>> are not part of the kernel-to-userspace contract.
>>>>>
>>>>>
>>>>> I think this is bogus for the kernel folks not allow a high
>>>>> precision timer in user space. Timers like this are needed for
>>>>> micro-benchmarking compiler changes along with other libc
>>>>> changes.
>>>>
>>>> According to the qemu bug the timers are optional.
>>>
>>> The generic timers are indeed optional, therefore we should not assume
>>> they are always present.  I don't want this to ship in 2.20 as is, so
>>> will back out the patch in the morning pending a better solution.
>>
>> Any solution for this yet?
>>
>> I was updating the HP_TIMING code for RHEL7 and noticed AArch64
>> still lacks HP_TIMING support.
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> Doesn't the server standard for armv8 require gti?  If so we can declare the standard glibc only for server base standard. And have an option later on for the other base standards.

The answer to my question is yes it is a requirement for Server Base
System Architecture Level 0 which means all server class systems have
it.  It also means nobody is not going to implement one processor
without GTI that is also going to use glibc.  So I think we should
just enable it by default for glibc and then when the day comes (if it
comes but I doubt it) have an option to disable the support for the
virtual timer.

Thanks,
Andrew



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> Thanks,
> Andrew
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>>
>> Cheers,
>> Carlos.
>>