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vdso: lower precision of vdso implementation of CLOCK_MONOTONIC_FAST and CLOCK_UPTIME_FAST

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so that libc vdso and kernel syscall give closer results.

Reported by:	dchagin
Reviewed by:	markj
Sponsored by:	The FreeBSD Foundation
MFC after:	1 week
Differential revision:	https://reviews.freebsd.org/D30873
This commit is contained in:
Konstantin Belousov 2021-06-23 02:24:08 +03:00
parent e912fbe167
commit 60b0ad10dd
1 changed files with 27 additions and 1 deletions
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28
lib/libc/sys/__vdso_gettimeofday.c
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@ -106,6 +106,30 @@ binuptime(struct bintime *bt, struct vdso_timekeep *tk, bool abs)
return (0);
}
static int
getnanouptime(struct bintime *bt, struct vdso_timekeep *tk)
{
struct vdso_timehands *th;
uint32_t curr, gen;
do {
if (!tk->tk_enabled)
return (ENOSYS);
curr = atomic_load_acq_32(&tk->tk_current);
th = &tk->tk_th[curr];
gen = atomic_load_acq_32(&th->th_gen);
*bt = th->th_offset;
/*
* Ensure that the load of th_offset is completed
* before the load of th_gen.
*/
atomic_thread_fence_acq();
} while (curr != tk->tk_current || gen == 0 || gen != th->th_gen);
return (0);
}
static struct vdso_timekeep *tk;
#pragma weak __vdso_gettimeofday
@ -154,9 +178,11 @@ __vdso_clock_gettime(clockid_t clock_id, struct timespec *ts)
break;
case CLOCK_MONOTONIC:
case CLOCK_MONOTONIC_PRECISE:
case CLOCK_MONOTONIC_FAST:
case CLOCK_UPTIME:
case CLOCK_UPTIME_PRECISE:
error = binuptime(&bt, tk, false);
break;
case CLOCK_MONOTONIC_FAST:
case CLOCK_UPTIME_FAST:
error = getnanouptime(&bt, tk);
break;