On Thu, 1 Sep 2022 17:09:55 +0200
Nico Boehr <nrb@xxxxxxxxxxxxx> wrote:
> Upcoming changes will do performance measurements of instructions. Since
> stck is designed to return unique values even on concurrent calls, it is
> unsuited for performance measurements. stckf should be used in this
> case.
>
> While touching that code, also add a missing cc clobber in
> get_clock_us() and avoid the memory clobber by moving the clock value to
> the output operands.
>
> Hence, add a nice wrapper for stckf to the time library.
>
> Signed-off-by: Nico Boehr <nrb@xxxxxxxxxxxxx>
> ---
> lib/s390x/asm/time.h | 11 ++++++++++-
> 1 file changed, 10 insertions(+), 1 deletion(-)
>
> diff --git a/lib/s390x/asm/time.h b/lib/s390x/asm/time.h
> index 7652a151e87a..8d2327a40541 100644
> --- a/lib/s390x/asm/time.h
> +++ b/lib/s390x/asm/time.h
> @@ -14,11 +14,20 @@
> #define STCK_SHIFT_US (63 - 51)
> #define STCK_MAX ((1UL << 52) - 1)
>
> +static inline uint64_t get_clock_fast(void)
> +{
> + uint64_t clk;
> +
> + asm volatile(" stckf %0 " : "=Q"(clk) : : "cc");
> +
> + return clk;
> +}
> +
> static inline uint64_t get_clock_us(void)
> {
> uint64_t clk;
>
> - asm volatile(" stck %0 " : : "Q"(clk) : "memory");
> + asm volatile(" stck %0 " : "=Q"(clk) : : "cc");
this fix is not needed if you use the wrapper for stck from your
other patch series
>
> return clk >> STCK_SHIFT_US;
> }
