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

[Marcus Shawcroft]

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.

/Marcus