[PATCH 3/5] s390: Fix vDSO clock_getres()

[Martin Schwidefsky]

On Mon,  1 Apr 2019 12:51:50 +0100
Vincenzo Frascino <vincenzo.frascino at arm.com> wrote:

> clock_getres in the vDSO library has to preserve the same behaviour
> of posix_get_hrtimer_res().
> 
> In particular, posix_get_hrtimer_res() does:
>     sec = 0;
>     ns = hrtimer_resolution;
> and hrtimer_resolution depends on the enablement of the high
> resolution timers that can happen either at compile or at run time.
> 
> Fix the s390 vdso implementation of clock_getres keeping a copy of
> hrtimer_resolution in vdso data and using that directly.
> 
> Cc: Martin Schwidefsky <schwidefsky at de.ibm.com>
> Cc: Heiko Carstens <heiko.carstens at de.ibm.com>
> Signed-off-by: Vincenzo Frascino <vincenzo.frascino at arm.com>
> ---
>  arch/s390/include/asm/vdso.h           |  1 +
>  arch/s390/kernel/asm-offsets.c         |  2 +-
>  arch/s390/kernel/time.c                |  1 +
>  arch/s390/kernel/vdso32/clock_getres.S | 17 ++++++++++++-----
>  arch/s390/kernel/vdso64/clock_getres.S | 15 ++++++++++-----
>  5 files changed, 25 insertions(+), 11 deletions(-)

I tried this patch and in principle this works. In that regard
Acked-by: Martin Schwidefsky <schwidefsky at de.ibm.com>

But I wonder if the loop to check the update counter is really
necessary. The hrtimer_resolution value can only changes once with
the first call to hrtimer_switch_to_hres(). With the TOD clock
as the only clock available on s390 we always have the ability
to do hrtimer. It then all depends on the highres=[on|off] kernel
parameter what value we get with clock_getres().

-- 
blue skies,
   Martin.

"Reality continues to ruin my life." - Calvin.