On Fri, 22 Feb 2019, Vincenzo Frascino wrote:
> +static notrace int __cvdso_clock_getres(clockid_t clock,
> + struct __vdso_timespec *res)
> +{
> + u64 sec, ns;
> + u32 msk;
> +
> + /* Check for negative values or invalid clocks */
> + if (unlikely((u32) clock >= MAX_CLOCKS))
> + goto fallback;
> +
> + /*
> + * Convert the clockid to a bitmask and use it to check which
> + * clocks are handled in the VDSO directly.
> + */
> + msk = 1U << clock;
> + if (msk & VDSO_HRES) {
> + /*
> + * Preserves the behaviour of posix_get_hrtimer_res().
> + */
So much for the theory.
> + sec = 0;
> + ns = MONOTONIC_RES_NSEC;
posix_get_hrtimer_res() does:
sec = 0;
ns = hrtimer_resolution;
and hrtimer_resolution depends on the enablement of high resolution timers
either compile or run time.
So you need to have a copy of hrtimer_resolution in the vdso data and use
that.
> + } else if (msk & VDSO_COARSE) {
> + /*
> + * Preserves the behaviour of posix_get_coarse_res().
> + */
> + ns = LOW_RES_NSEC;
> + sec = __iter_div_u64_rem(ns, NSEC_PER_SEC, &ns);
Do we allow CONFIG_HZ = 1?
Thanks,
tglx
