On Wed, Sep 08, 2021 at 12:02:09PM +0200, Nicolas Saenz Julienne wrote:
> Some architectures have special purpose registers to query the system
> timer's frequency. Let's use that when available.
>
> Signed-off-by: Nicolas Saenz Julienne <nsaenzju@xxxxxxxxxx>
> ---
> src/oslat/oslat.c | 20 +++++++++++++++++++-
> 1 file changed, 19 insertions(+), 1 deletion(-)
>
> diff --git a/src/oslat/oslat.c b/src/oslat/oslat.c
> index bd155a6..23ca9b6 100644
> --- a/src/oslat/oslat.c
> +++ b/src/oslat/oslat.c
> @@ -51,6 +51,9 @@
> # define atomic_inc(ptr) __sync_add_and_fetch((ptr), 1)
> # if defined(__x86_64__)
> # define relax() __asm__ __volatile__("pause" ::: "memory")
> +
> +#define measure_timer_mhz generic_measure_timer_mhz
> +
> static inline void frc(uint64_t *pval)
> {
> uint32_t low, high;
> @@ -61,12 +64,18 @@ static inline void frc(uint64_t *pval)
> }
> # elif defined(__i386__)
> # define relax() __asm__ __volatile__("pause" ::: "memory")
> +
> +#define measure_timer_mhz generic_measure_timer_mhz
> +
> static inline void frc(uint64_t *pval)
> {
> __asm__ __volatile__("rdtsc" : "=A" (*pval));
> }
> # elif defined(__PPC64__)
> # define relax() do { } while (0)
> +
> +#define measure_timer_mhz generic_measure_timer_mhz
> +
> static inline void frc(uint64_t *pval)
> {
> __asm__ __volatile__("mfspr %0, 268\n" : "=r" (*pval));
> @@ -74,6 +83,15 @@ static inline void frc(uint64_t *pval)
> # elif defined(__aarch64__)
> # define relax() __asm__ __volatile("yield" : : : "memory")
>
> +static inline unsigned int measure_timer_mhz(void)
> +{
> + unsigned int val;
> +
> + __asm__ __volatile__("mrs %0, cntfrq_el0" : "=r" (val));
> +
> + return val / 1e6;
> +}
> +
> static inline void frc(uint64_t *pval)
> {
>
> @@ -257,7 +275,7 @@ static cycles_t __measure_timer_hz(void)
> return (cycles_t) ((e - s) / sec);
> }
>
> -static unsigned int measure_timer_mhz(void)
> +static unsigned int __attribute__((unused)) generic_measure_timer_mhz(void)
This is okay I guess, but does not look nice, as it's marked unused even if
it's used..
How about for any arch that supports a faster version to read the freq, do:
#define measure_timer_mhz_fast
unsigned int measure_timer_mhz_fast(void)
{
...
}
Then at entry of measure_timer_mhz():
#ifdef measure_timer_mhz_fast
return measure_timer_mhz_fast();
#endif
I'm also wondering the diff between the two methods on arm64 and whether
there's a huge difference on the numbers.
Thanks,
--
Peter Xu
