Re: [RFC PATCH 1/5] x86: tsc: add tsc to art helpers

Thomas Gleixner
2019-07-16T07:57:53Z

Felipe,

On Tue, 16 Jul 2019, Felipe Balbi wrote:

-ENOCHANGELOG

As you said in the cover letter:

> (3) The change in arch/x86/kernel/tsc.c needs to be reviewed at length
> before going in.

So some information what those interfaces are used for and why they are
needed would be really helpful.

> +void get_tsc_ns(struct system_counterval_t *tsc_counterval, u64 *tsc_ns)
> +{
> + u64 tmp, res, rem;
> + u64 cycles;
> +
> + tsc_counterval->cycles = clocksource_tsc.read(NULL);
> + cycles = tsc_counterval->cycles;
> + tsc_counterval->cs = art_related_clocksource;
> +
> + rem = do_div(cycles, tsc_khz);
> +
> + res = cycles * USEC_PER_SEC;
> + tmp = rem * USEC_PER_SEC;
> +
> + do_div(tmp, tsc_khz);
> + res += tmp;
> +
> + *tsc_ns = res;
> +}
> +EXPORT_SYMBOL(get_tsc_ns);
> +
> +u64 get_art_ns_now(void)
> +{
> + struct system_counterval_t tsc_cycles;
> + u64 tsc_ns;
> +
> + get_tsc_ns(&tsc_cycles, &tsc_ns);
> +
> + return tsc_ns;
> +}
> +EXPORT_SYMBOL(get_art_ns_now);

While the changes look innocuous I'm missing the big picture why this needs
to emulate ART instead of simply using TSC directly.

Thanks,

tglx