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| author | Konstantin Belousov <kib@FreeBSD.org> | 2021-06-22 23:24:08 +0000 |
|---|---|---|
| committer | Konstantin Belousov <kib@FreeBSD.org> | 2021-06-23 21:36:33 +0000 |
| commit | 60b0ad10dd0fc7ff6892ecc7ba3458482fcc064c (patch) | |
| tree | 03a53983d09dcdf4faf803ef1271765f1ee75a35 | |
| parent | e912fbe1675714aab0179999923c171615e78c07 (diff) | |
| download | src-60b0ad10dd0fc7ff6892ecc7ba3458482fcc064c.tar.gz src-60b0ad10dd0fc7ff6892ecc7ba3458482fcc064c.zip | |
vdso: lower precision of vdso implementation of CLOCK_MONOTONIC_FAST and CLOCK_UPTIME_FAST
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
| -rw-r--r-- | lib/libc/sys/__vdso_gettimeofday.c | 28 |
1 files changed, 27 insertions, 1 deletions
diff --git a/lib/libc/sys/__vdso_gettimeofday.c b/lib/libc/sys/__vdso_gettimeofday.c index 4c1f4bda23e1..c1457a54d37e 100644 --- a/lib/libc/sys/__vdso_gettimeofday.c +++ b/lib/libc/sys/__vdso_gettimeofday.c @@ -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; |